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COVID-19 - Epidemeology

A group of 239 experts from 32 countries sent an open letter to the World Health Organization 6 July 2020, saying that tiny particles smaller than droplets may linger in the air for hours, infecting people even in socially-distant settings. That's contrary to the WHO, which has long insisted that the primary mode of transmission is large respiratory droplets that quickly fall to the ground, and that airborne transmission only occurs in hospital during medical procedures. Even until very recently, it has denied the possibility of airborne transmission, citing lack of evidence.

Excess malaria deaths caused by pandemic driven shortfalls in prevention and treatment efforts will probably dwarf direct deaths from covid-19 in sub-Saharan Africa, the World Health Organization has warned. Progress against malaria—dramatic in the first decade of this century—had already stalled since 2016 as foreign donors drifted away. But 2020 is likely to be the first year in decades to see an increase in deaths, WHO warned in its 2020 World Malaria Report 03 December 2020.

After the COVID-19 outbreak in Wuhan, several groups reported SARS-related coronavirus in horseshoe bats in China and in pangolins smuggled from South Asian countries. But according to genome sequence comparison, none are directly the source of SARS-CoV-2, the agent of COVID-19. In the meantime, COVID-19 infections in mink farms have been reported in eight countries, including the Netherlands, France, Italy and the US, according to the WHO. There is limited evidence of animal-to-human transmission of SARS-CoV-2 except for mink.

Even if a vaccine is developed, that does not mean the end of the pandemic. That's according to Professor Oh Myoung-don, who leads Korea's central clinical committee for emerging disease control. He explained 25 August 2020 that when it comes to respiratory diseases, vaccines aren't a silver bullet. "It's not easy to replicate the immunogenicity of respiratory viruses and the germs that cause respiratory infections. For example, flu vaccines have an efficacy rate of 60 to 70 percent. Another important fact is that COVID-19 is an RNA virus, so it continues to mutate."

Other studies have found that the virus has mutated, making it more infectious than before. In a study published in the journal Cell, the new "G variant" of the coronavirus is dominant globally, and is 6 times more infectious than the previous version.

The UK Covid-19 variant, dubbed VOC 202012/01 or B.1.1.7, quickly became responsible for nearly 50 per cent of cases in the UK, before spreading around the world. Out of that variant, a new variant has evolved, which is far more contagious and transmissible. In an ironic twist, while the newest variant is not more lethal, in the grand scheme it’s higher transmissibility has a higher chance of causing more deaths in a population because it causes more infections than the original Covid-19 virus. The variant’s first mutation affected its ‘spike protein’, the receptor that allows the virus to latch on to cells.

The virus has undergone a more recent mutation, described as E484K in a United Kingdom public health briefing document on February 1 2021. Unlike the N501Y mutation that made the UK variant more contagious, the E484K mutation switches a negatively charged acid for a positive one, making it incredibly difficult for a bodies antibodies to identify and latch onto the virus.

The new coronavirus variant found in the UK that shares characteristics with variants dominant in the South African coronavirus variant (B.1.351) and in Brazil (P.1) are causing many Westerners to worry about reduced vaccine efficacy. The new E484K variant is also present in the family of variants that caused COVID-19 flare-ups in South Africa and Brazil. Apart from being 25- to 40-percent more contagious than other sequences of the virus, studies suggested the mutations are more deadly, evident in the surging number of critically ill patients among elderly. US chief immunologist Anthony Fauci had warned that the mutations could cause "a very high rate of reinfection" among people who had contracted the previous dominant sequences of the virus.

Vaccine effectiveness is a deeply concerning issue in the face of viral mutations. On January 29, Johnson and Johnson reported that their vaccine was only 72 per cent effective in the US, and only 57 per cent effective in South Africa. The new South African covid-19 is already dominant in the country, and is likely responsible for the disparity in figures. Novavax also reported that its vaccine was only 85 per cent effective against the UK variant, and only 50 per cent effective against the South African variant. Vaccines can be redesigned in two months to tackle new variants. The adjusted vaccines could be either a new version of a vaccine or an additional shot that will be used in combination of a current version.

A September 2020 study from the University of California San Francisco suggested that masks protect the wearer from contracting COVID-19. Dr. Monica Gandhi, the UCSF infectious disease doctor who led the study said that new research showed the severity of a person’s COVID-19 symptoms can depend on how much of the virus enters the body. “How much virus you get in is probably one of the most important determinants of how sick you get,” she said. “By having a mask over your face, it filters out the majority of viral particles. So, even if you do get exposed to COVID… you are going to get very little virus in, and if you do get COVID, you’ll get less sick.” The report will be published in the Journal of General Internal Medicine.

Individuals in Belgium and the Netherlands have been reinfected with the coronavirus, Dutch media eeported 25 August 2020. Virologist Marion Koopmans said it was more common for people to remain infected with the virus for a long time, but with mild symptoms, before it suddenly flares up again. A reinfection — as is the case with the Dutch and Belgian cases — requires genetic testing in both the first and second instances of infection to see whether there are differences in the virus present. The development shows that the antibodies the patient developed in the first case were not strong enough to fend off an infection from a slightly different variant of the virus. The immune responses to this virus are exactly what would be expected. The fact that somebody may get reinfected is not surprising. But the reinfection didn’t cause disease.

After persuading his country to avoid a strict lockdown, Sweden’s top epidemiologist admitted 02 June 2020 that his strategy for Covid-19 resulted in too many deaths. The Swedish coronavirus strategy was originally built on two pillars: one, to flatten the curve of the spread of infections in order to make sure that the public health care system would not burst at the seams, and, two, protecting the elderly population. But in Sweden's first antibody study, fewer people than predicted had developed coronavirus antibodies – just 7.3 percent in Stockholm by early April. Tegnell said, among other things, that Sweden should have taken more measures against the corona virus from the beginning. At 43 deaths per 100,000, Sweden’s mortality rate is among the highest globally and far exceeds that of neighboring Denmark and Norway.

Annika Linde, Sweden's former state epidemiologist, stated 28 May 2020 that though she initially supported the national coronavirus strategy, she believed a lockdown could have saved lives and calls for more humility. Linde, has spoken out by criticising some of the most prominent supporters of the Swedish strategy, notably her and Tegnell's predecessor and honorary WHO adviser Johan Giesecke, who made both domestic and international headlines for being a strong defender of the Swedish approach. Linde believes Sweden would probably have benefited from imposing a lockdown – even if only for a month.

While most of the world had gone into some version enforced social distancing and quarantine mode with the rise of COVID-19, the 10 million Swedish residents faced no official hurdles to life proceeding as normal. As of early April, around half the Swedish workforce is now working from home, and public transport usage has fallen by roughly 50 percent. The streets in the nation’s capital, Stockholm, are 70 percent less busy than usual. But Swedish students under 16 were in school, restaurants were less full but still operational and haircuts were still an available service. People are even still going to nightclubs. Under conservative epidemiological parameter estimates, the Swedish public-health strategy will result in a peak intensive-care load in May that exceeds pre-pandemic capacity by over 40-fold, with a median mortality of 96,000 (95% CI 52,000 to 183,000). But as of April 15,these predictions were an order of magnitude off from actual observations. Covid19-induced ICU cases were reported at approximately 500, current hospitalized cases at 2100, accumulated deaths at 1200, and accumulated detected cases at 12000.

Sweden’s Chief Epidemiologist Anders Tegnell stated that the nation’s COVID-19 strategy is rooted in a “long tradition of respecting free will.” Tegnell has defended Sweden’s more relaxed approach to combating the coronavirus as both sufficient to protecting the public health and more realistically sustainable over the long term than the measures its European neighbors have put in place. Sweden — given its unique demographic factors such as the fact that 50 percent of the population lives alone, or that its population density is approximately one-tenth that of the U.K or Italy — might be unusually well suited to a more hands-off, less socially and economically disruptive approach to social distancing.

Compared to its demographically similar Scandinavian neighbors Denmark, Norway and Finland, the difference is quite striking. Denmark had 321 deaths; Norway had 150 and Finland had 75. Sweden has the largest population of the four, with roughly 10 million citizens to about 5 million in the other three nations. Sweden had a relatively high case fatality rate: as of April 8, 7.68% of the Swedes who have tested positive for COVID-19 have died of the virus. More people were dying, with 10.14 deaths per 100,000 people in Sweden versus 5.16 and 2.62 in Denmark and Norway, as of Feb. 15. The average age of those dying in Sweden was markedly higher than in Norway. “I

More than 18,600 people had been infected in the country of about 10 million by 27 April 2020, and nearly 2,200 had died. Neighbouring Denmark, with a population of nearly six million, has seen more than 8,700 cases with at least 400 deaths, while Norway, with a population of 5.3 million, has reported 7,500 infections and just over 200 deaths.

Analysts led by Sumit Kumar Mishra of India's CSIR National Physical Laboratory and Alfred Wiedensohler and Ajit Ahlawat of Germany's Leibniz Institute for Tropospheric Research (TROPOS) concluded in August 2020 that humidity affected viral spread in three ways: droplet size, how viral-loaded aerosols float for "hours," and stay viral on landing surfaces. In humid places, the viral droplet — a solution of salts, water, organics and attached viruses — grows and it falls faster, "providing less chances for other people to breathe in infectious viral droplets."

But in dry indoor air, micro-droplets shrunk by evaporation become lighter and stay adrift — an "optimal route" for viruses to be "inhaled by other residents, or finally settle on surfaces where they can survive for many days," warns the report. Maintaining relative room humidity at between 40% and 60%, "like opening of windows," they say, can also reduce absorption of viruses though a person's nasal passages.

Initially some thought the corona season will end with the beginning of spring in the northern hemisphere, but over time it became clear that this was not the case. While seasonal flu outbreaks can happen as early as October, the flu season typically lasts from November to March, and most of the time flu activity peaks between December and February, although activity can last as late as May. Flu is unpredictable and seasons can vary.

The authors of one study by Mohammad M. Sajadi et al, which was published 09 March 2020, wrote that COVID-19 “has established significant community spread in cities and regions only along a narrow east-west distribution roughly along the 30-50 North latitude corridor at consistently similar weather patterns (5-11 degrees C [41 to 51 F] and 47-79 percent humidity). ... Notably, during the same time, COVID-19 failed to spread significantly to countries immediately south of China,” the paper notes. “The number of patients and reported deaths in Southeast Asia is much less when compared to more temperate regions noted ... The association between temperature in the cities affected with COVID-19 deserves special attention.”

In a paper published in January 2021 in Evolutionary Bioinformatics, researchers from the University of Illinois, Chicago suggested that, among other epidemiological metrics, the rise in COVID-19 cases and coronavirus-related mortality rates were significantly affected by temperature and altitude across 221 countries. “One conclusion is that the disease may be seasonal, like the flu. This is very relevant to what we should expect from now on after the vaccine controls these first waves of COVID-19,” according to Gustavo Caetano- Anollés, to Medical Xpress, the senior author of the research paper. He is professor at the Department of Crop Sciences, and affiliate of the Carl R. Woese Institute for Genomic Biology Illinois.

The researchers found that temperature and latitude correlated with the rise in COVID-19 cases, realizing then that climate was only one factor that contributed to the global COVID-19 incidence. “Indeed, our worldwide epidemiological analysis showed a statistically significant correlation between temperature and incidence, mortality, recovery cases, and active cases. The same tendency was found with latitude, but not with longitude, as we expected,” said Caetano-Anollés. “Our results suggest the virus is changing at its own pace, and mutations are affected by factors other than temperature or latitude. We don’t know exactly what those factors are, but we can now say seasonal effects are independent of the genetic makeup of the virus.”

The United Kingdom's chief scientific adviser has said models indicate about 60 percent of a given community would need to be immune to reach herd immunity for the new coronavirus, SARS-CoV-2. However, questions remain how immune a recently recovered coronavirus patient actually is, and how long that immunity lasts.

On 04 April 2020 the Institute for Health Metrics and Evaluation reported "To date, the relationship between temperature and estimated changes in transmission appears to modest for our currently included locations. However, this could be more related to the limited months and time of year – March to April – than how temperature could affect COVID-19 trends as the Northern Hemisphere moves toward summer. It is very possible temperature will become a stronger predictor into May and June."

A report published 01 May 2020 by infectious disease experts, Kristine A. Moore, Marc Lipsitch, John M. Barry, and Michael T. Osterholm at the University of Minnesota’s Center for Infectious Disease Research and Policy. said the novel coronavirus pandemic is behaving more like past influenza pandemics than other coronavirus outbreaks. So officials should plan for the worst case scenario for the coronavirus pandemic, which would include a second peak of cases this fall and no vaccine or herd immunity.

At a White House news conference on 23 April 2020, a senior Department of Homeland Security (DHS) official said government scientists studying what conditions will kill the COVID-19 coronavirus had found the virus dies quickly when exposed to sunlight, heat, humidity and cleaning chemicals like bleach and isopropyl alcohol. During the White House Coronavirus Task Force briefing, DHS Science and Technology Directorate chief William Bryan presented reporters with the first results from studies by the National Biodefense Analysis and Countermeasures Center on what conditions the COVID-19 novel coronavirus can survive in. Bryan told reporters the virus dies “at a much more rapid pace” when exposed to higher temperatures and humidity, noting that at 75 degrees Fahrenheit and 80% humidity, it dies much faster than before, in between one and six hours. However, when exposed to direct summer sunlight under those conditions, the virus perishes in just two minutes.

However, while he conceded that “summer conditions will create an environment where transmission can be decreased,” he was careful to add that “it would be irresponsible to say that we feel the summer will totally kill the virus".

Juanjuan Zhang et al found that "... children 0-14 years are less susceptible to SARS-CoV-2 infection than adults 15-64 years of age (odds ratio 0.34, 95%CI 0.24-0.49), while in contrast, individuals over 65 years are more susceptible to infection (odds ratio 1.47, 95%CI: 1.12-1.92). ... While proactive school closures cannot interrupt transmission on their own, they can reduce peak incidence by 40-60% and delay the epidemic."

Terry C. Jones et al found that "Analysis of variance of viral loads in patients of different age categories found no significant difference between any pair of age categories including children. In particular, these data indicate that viral loads in the very young do not differ significantly from those of adults. Based on these results, we have to caution against an unlimited re-opening of schools and kindergartens in the present situation. Children may be as infectious as adults."

The coronavirus is surrounded by a lipid layer, in other words, a layer of fat. This layer is not very heat-resistant, which means that the virus quickly breaks down when temperatures rise. Air humidity also influences the transmissibility of respiratory viruses. Once the pathogens have been expelled from the respiratory tract with a strong sneeze, they literally hang in the air. On cold and usually dry winter days, the small droplets, together with the viruses, float in the air longer than when the air humidity is high.

Dr Stefan Baral, an epidemiology expert at Johns Hopkins University, was quoted by the Boston Herald as saying he expects "a natural decrease" of the disease as the United States moves into warmer weather. AccuWeather, the US-based forecaster, quoted Dr John Nicholls, a pathology professor at the University of Hong Kong, saying there are three things coronavirus does not like: sunlight, temperature and humidity. "Sunlight will cut the virus's ability to grow in half, so the half-life will be 2.5 minutes, and in the dark it's about 13 to 20 [minutes]. Sunlight is really good at killing viruses," Nicholls said. Deutsche Welle also cited Thomas Pietschmann, a virologist from Germany's Centre for Experimental and Clinical Infection Research, who said the coronavirus is "not very heat-resistant, which means that the virus quickly breaks down when temperatures rise".

According to AccuWeather, spring would arrive in the US on March 19, while Climate-Data.org is predicting that temperatures in the Italian capital of Rome will climb to 16C-17C (60.8-62.6F), when the spring equinox arrives in Europe on March 20. Even as the weather warms up in the northern hemisphere, the coronavirus may still survive for days at temperatures up to 25C (77 F),

But the swine flu of 2009 is a cautionary tale, said David N. Fisman, a professor of epidemiology at the University of Toronto. It showed up in New York in April that year, well after the traditional peak of flu season, and by June, it was classified as an epidemic.

A research team led by Chinese top respiratory specialist Zhong Nanshan found that the median incubation period of the coronavirus disease was four days and nearly half of the patients did not have a fever when first admitted to the hospital. The team delineated the clinical characteristics of COVID-19 disease in China based on a dataset of 1,099 patients from 552 hospitals across the country during the first two months of the outbreak, in a research article published 28 February 2020 in The New England Journal of Medicine, a prestigious medical journal. The research found that the median incubation period of the disease was four days, with an interquartile range from two to seven days. Researchers recalculated the data after stripping out the extreme cases. Two patients from the sample were found with an incubation period of as long as 24 days, and for those living in Wuhan, Hubei Province for a long time or in contact with Wuhan residents, the incubation period was usually zero days.

Hubei Province reported 1,638 new cases of novel coronavirus pneumonia on Feb 11, with 94 new deaths and 417 cases of recovery. The total number of infections in the province climbed to 33,366, with 1,068 deaths and 2,639 cases of recovery. Hubei on 13 February 2020 announced 14,840 new cases, including 13,332 clinically diagnosed cases, with 242 new deaths. The total number of infections in the province climbed to 48,206, with 1,310 deaths.

The skyrocketing number of new cases in Hubei came after health officials announced they had begun including people diagnosed using new clinical methods in official statistics. Clinical diagnosis of COVID-19, as the virus was officially named, would now include lung imaging to verify suspected infections. Previous diagnostic methods were restricted to nucleic acid tests, which identify genetic information to detect viruses but can take days to process.

Early on, many of the patients in the outbreak in Wuhan, China reportedly had some link to a large seafood and animal market, suggesting animal-to-person spread. However, a growing number of patients reportedly had not had exposure to animal markets, indicating person-to-person spread was occurring. Initially it was unclear how easily or sustainability this virus is spreading between people. The virus, different from SARS, can infect people even if its carrier shows no or few symptoms.

Some viruses are highly contagious (like measles), while other viruses are less so. It’s important to know this in order to better understand the risk associated with the Wuhan virus. The reproduction number R0 [pronounced “R naught”] is a mathematics term that indicates how contagious an infectious disease is. If R0 is more than 1, each existing infection causes more than one new infection. The R0 value of the 1918 flu pandemic was estimated to be between 1.4 and 2.8, while Ebola currently has an R0 of about 1.5 to 2. SARS and HIV have an R0 of about 4, while Measles has an R0 of 12-18, meaning a person who has measles will transmit it to an average of a dozen to a dozen and a half other people.

The R0 for the Wuhan novel Coronavirus was initially estimated in the range 1.4 to 2.6 (lower than the 3.8 initial reports). "We estimate that, on average, each case infected 2.6 (uncertainty range: 1.5-3.5) other people up to January 18, 2020, based on an analysis combining our past estimates of the size of the outbreak in Wuhan with computational modeling of potential epidemic trajectories,” according to a report by scientists at Imperial College London released 25 January 2020. By other reputable estimates, the range looks like 2 to 3.8.

The longer the infectious period of a disease, the more likely an infected person is to spread the disease. Adults with the flu are typically contagious for up to eight days, while children may be contagious for up to two weeks. National Health Commission Minister Ma Xiaowei said on 26 January 2020 that the incubation period for nCoV could range from one to 14 days, not a particularly helpful estimate. A paper published 24 January 2020 that described transmission within a family in Hong Kong suggested the incubation time — the time from infection to the development of symptoms — may be a bit shorter than that of SARS. With SARS, most people developed symptoms about four or five days after infection. China's medical authority stated on 28 January 2020 the incubation period of novel coronavirus was usually 3-7 days.

The incubation period for the coronavirus could be longer than expected: on 10 February 2020 a patient in Central China's Henan, with no symptoms for 17 days, was diagnosed as an infected patient. The incubation period for people infected with nCoV could reach up to 24 days, stated an academic paper published 10 February 2020 by renowned Chinese respiratory expert Zhong Nanshan. Previously, the longest incubation period was believed to be 14 days.

The Wuhan novel coronavirus is apparently contagious before symptoms appear. The SARS virus did not transmit before people developed symptoms, so screening at transportation hubs for people with fevers was an effective measure in containment. Professor Mitsuo Kaku of Tohoku Medical and Pharmaceutical University said "The Chinese have confirmed cases in which carriers without symptoms have spread the virus. If it can be contagious even in the incubation period when it is only present in the body in small quantities, it will be extremely difficult to contain." Li Xingwang, a member of the Chinese government's team of medical experts, told reporters on 28 January 2020 that people with only mild symptoms, as well as those who are infected but have not yet developed symptoms, are capable of spreading the virus. He said this has hampered efforts to prevent and control infections. . WHO's announcement, that the new coronavirus can be transmitted during incubation period added to the fears of the virus spread. South Korean government, however, said 29 January 2020 it was highly unlikely that the virus can be transmitted from a patient with no symptoms.

Coronaviruses are generally thought to be spread most often by respiratory droplets. In general, because of poor survivability of these coronaviruses on surfaces, there is likely very low risk of spread from products or packaging that are shipped over a period of days or weeks at ambient temperatures.

This virus is not an airborne infection, rather a droplet infection. The difference between these are the size of the particles that come out of one's mouth. As the novel coronavirus particles are relatively large, people more than two meters away are generally safe.

Feng Luzhao, a researcher at the Infectious Diseases Division of the Chinese Center for Disease Control and Prevention told state broadcaster CCTV on 09 February 2020 that the main transmission route is via droplets and contact. Feng's comments ran counter to earlier warnings in state media that everyone should wear masks if they go outside, and to state media reports of suspected airborne transmission routes. "At present, the main route of transmission of new coronaviruses is droplet transmission and contact transmission," Feng told CCTV. "There is currently no evidence that nCoV is capable of airborne transmission." Feng said "The transmission distance is very short, usually one to two meters. "The virus will remain suspended or floating in the air for any length of time."


As of 27 January 2020 the disease had killed at least 81 people and infected at least 2,744 in China. This suggested a mortality rate of about 3%, which is high. The mortality rate of normal influence is about 0.1%. In the United States, the overall burden of normal seasonal influenza for the 2017-2018 season was an estimated 45 million influenza illnesses, 21 million influenza-associated medical visits, 810,000 influenza-related hospitalizations, and 61,000 influenza-associated deaths. The "Spanish" influenza pandemic of 1918–1919, was exceptionally severe, with case-fatality rates of greater than 2.5%. SARS had a mortality rate of 11%, and Ebola at one time had a 40-70% mortality rate.

As of 22 January 2020, Chinese authorities had presented epidemiological information that revealed an increase in the number of cases, of suspected cases, of affected provinces, and the proportion of deaths in currently reported cases of 4% (17 of 557). Of confirmed cases, 25% were reported to be severe.

The apparent 3% case-fatality rate of the Wuhan novel coronaviruses (COVID-19) is probably an over-estimate, as it counts all deaths, while many mild cases of the disease go un-reported. Scientists at the University of Hong Kong (HKU) warned their latest models show the number of actual infections was likely to be much higher than the official tolls, which only account for those who have been found and have tested positive. As many as 44,000 people may have been infected as of 25 January 2020. HKU team lead Gabriel Leung said the number of infections would likely double every six days, peaking in April and May for those places currently dealing with an outbreak, although effective public health measures could bring that rate down. Possibly the six day doubling time will slow, as it implies that everyone on the planet would have contracted the virus by early May 2020. Running the six-day doubling time backwards suggests there were possibly 5,000 cases in early January, suggesting a case-fatality rates of possibly 1.5%.

It was expected that further international exportation of cases may appear in any country. Thus, all countries should be prepared for containment, including active surveillance, early detection, isolation and case management, contact tracing and prevention of onward spread of COVID-19 infection. Some Chinese experts said the outbreak could reach its peak by mid-February while some experts in Hong Kong claimed it would peak in April or May, infecting more than hundred-thousand people.

Zhou Xianwang, the mayor of Wuhan, said at a press conference on 26 January 2020 that more than 5 million people had left the city because of the Spring Festival and the epidemic. The news came as quite a shock. Where have these 5 million people gone? How many of them are carriers of the new coronavirus? How many people will be infected because of them?

Nearly 70 percent of trips out of Wuhan were within Hubei province, while another 14 percent went to the neighboring provinces of Henan, Hunan, Anhui and Jiangxi, the Associated Press reported 20 February 2020, cited Baidu maps data. Some two percent went to the southern province of Guangdong, while others "fanned out across China," the report said, adding: "The travel patterns broadly track with the early spread of the virus." molecular virologist Jin Dong-Yan of Hong Kong University’s School of Biomedical Sciences told the AP "It’s definitely too late.... Five million out. That’s a big challenge.... To control this outbreak, we have to deal with this. On one hand, we need to identify them. On the other hand, we need to address the issue of stigma and discrimination".

Despite some cases of recovered patients testing positive again for COVID-19, a top expert in Shanghai brushed off the concerns saying there has been no case reported that confirms such patients would transmit the virus to others. "Based on the national data, no case has been reported that confirms the coronavirus patients who test positive after recovery are infectious," Zhang Wenhong, head of the Shanghai COVID-19 medical expert team, told a press conference in Shanghai on 29 February 2020.

Guangdong health authorities announced 25 February that 13 recovered COVID-19 patients tested positive again in later diagnosis, and that about 14 percent of the total recovered patients in Guangdong tested positive later. There are two possibilities that result in some recovered patients testing negative twice initially but positive after discharge from hospital: one is the sample is taken from patients' laryngeal part of pharynx while the patient is at a low viral load at the critical point, and the other possibility is the sample quality is not good, said Zhang.

On 14 February 2020, the US Centers for Disease Control and Prevention (CDC) said they will begin to test individuals with influenza-like-illness for the novel coronavirus at public health labs in Los Angeles, San Francisco, Seattle, Chicago, and New York City. However, it is unknown whether Americans who have already died of the influenza had contracted the coronavirus, as reported by TV Asahi.

The story sparked various conspiracy theories on Chinese cyberspace. The Military World Games were held in Wuhan in October. "Perhaps the US delegates brought the coronavirus to Wuhan, and some mutation occurred to the virus, making it more deadly and contagious, and causing a widespread outbreak this year," a user posted on China's Twitter-like Sina Weibo.

Shen Yi, an international relations professor at the Shanghai-based Fudan University, noted that global virologists are working to track the origin of the virus, including the intelligence agencies. Netizens are encouraged to actively partake in discussions, but preferrably in a rational fashion. "The symptoms and the contagiosity of the COVID-19 are evident to all. It is impossible to conceal the origins of the disease," Shen said, urging the public to rely more on facts.

The epidemic is a major test for many systems and media should report in a clear and accurate manner. Asahi's report is actually using ambiguous Japanese expressions to lead readers to think that the COVID-19 is more serious than it appeared to be in the US, he added. US officials have so far confirmed 35 cases of the novel coronavirus in the country. Media reported the US CDC has been working with the healthcare sector to heighten preparedness before the virus "take(s) a foothold in the US."

Reuters quoted US health officials as saying, they are preparing for the possibility of the spread of the new coronavirus through US communities that would force closures of schools and businesses. The US is concerned that a larger spread of the COVID-19 coronavirus could overwhelm emergency rooms, and cause supply shortages of some crucial medical supplies, during an already busy time dealing with seasonal flu.

“Social distancing will help reduce the number of infected people needing medical assistance in hospitals at a given moment, to allow the healthcare system to better cope with it,” he added. “But that might not be all. When those measures are lifted, if there isn’t sufficient herd immunity in a community, due to either natural immunity or a vaccine that’s developed, then there is a very high likelihood that the epidemic starts up again.”

The findings of a study published by Imperial College London (ICL) in March 2020 corroborate this. According to the ICL experts, the only way to effectively curb the contagion would be to keep social distancing in effect until a vaccine is made available - which might take up to 18 months if everything works as it should. This would clearly have an unbearable social and economic cost, which the study proposes to mitigate by implementing a ‘waveform’ social distancing: When the spread of the disease seems to decrease, the quarantine measures would be loosened, to be tightened again when the contagion reaches dangerous levels.

Talib Dbouka and Dimitris Drikakis reported "For a mild human cough in air at 20 ?C and 50% relative humidity, we found that human saliva-disease-carrier droplets may travel up to unexpected considerable distances depending on the wind speed. When the wind speed was approximately zero, the saliva droplets did not travel 2 m, which is within the social distancing recommendations. However, at wind speeds varying from 4 km/h to 15 km/h, we found that the saliva droplets can travel up to 6 m with a decrease in the concentration and liquid droplet size in the wind direction. Our findings imply that considering the environmental conditions, the 2 m social distance may not be sufficient."



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