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Homeland Security

Flu Pandemic Mitigation

A wide range of non-medical interventions - from personal hygiene and the wearing of masks to quarantine and the screening of travellers - can potentially reduce opportunities for transmission and slow international spread. Although many of these non-medical interventions were tested during the emergency response to SARS, their use during the different conditions of an influenza pandemic has not been systematically evaluated. Consideration of their use during a pandemic is particularly important, as non-medical interventions will be the principal protective tools so long as supplies of effective vaccines and antivirals remain scarce.

The effectiveness of many interventions will depend on the behavior of the virus as determined by its pathogenicity, principal mode of transmission (droplet or aerosol), attack rate in different age groups, duration of virus shedding, and susceptibility to antivirals. If, for example, it is known that children are the most severely affected age group, or play a major role in transmission, health authorities will be in a better position to make decisions about the effectiveness of school closure, travel measures (children travel less frequently than adults), and quarantine (children cannot be separated from their parents).

Practical and common sense measures, such as frequent handwashing, covering your mouth and nose while sneezing or coughing, and staying home from work or school if you are ill with influenza-like illness, may be important to help prevent the spread of pandemic influenza. Respiratory viruses such as those those that cause flu are highly contagious and can survive for two days on skin, furniture, doorknobs and other hard surfaces. A clinical study on hand washing has shown a reduction in total respiratory illnesses although the study subjects were not tested specifically for influenza. A separate study demonstrated that hand sanitation using a commercially available ethanol-based hand rub had viricidal activity against influenza viruses. Although the effectiveness of hand washing or the use of other forms of hand hygiene on influenza transmission have not been studied, this measure is prudent based on the available data and the relative ease of instituting hand hygiene measures.

The influenza virus can survive on surfaces for hours to days, depending on the surface, but it survives on hands for less than 5 minutes. Hand washing has been shown to reduce transmission of respiratory illness, in general, in the specific setting of military trainees, but there is no specific scientific evidence related to flu. While it is reasonable to recommend that those who are in contact with the sick wash their hands, there is no evidence to support the notion that frequent routine hand washing during an epidemic will provide additional protection against transmission of the virus.

The ability of containment strategies to substantially slow the spread of pandemic influenza may be limited by the short incubation period for influenza, the large proportion of asymptomatic infections, and the non-specific nature of clinical illness from influenza infection. These challenges may lead to difficulty in identifying infected persons, in quarantining contacts of infected person prior to onset of illness, and in marshalling the substantial resources that would be needed to initiate and monitor the use of containment measures.

Opportunities for averting a pandemic or appreciably slowing its spread would end once efficient and sustained human-to-human transmission was established, as the containment of influenza at this stage is considered virtually impossible. At some point, efforts to prevent international spread through travel-related measures would also become ineffective. As levels of morbidity and mortality mount during a pandemic, measures that made good sense at earlier phases - such as isolation of patients, contact tracing, and voluntary quarantine of contacts - would cease to be effective or feasible. During prior pandemics, use of masks, closing of schools, and restrictions on large public gatherings and meetings were recommended to prevent community spread. These strategies, however, generally were not found to be effective, possibly because they tended to be instituted late in the outbreak and were not strictly adhered to, or because the control measures were not appropriate to the principle modes of transmission of influenza virus. Successful quarantines were rare.

Even during severe pandemics not everyone is affected, opening opportunities to maximize the proportion who remain uninfected. In this phase, measures such as simple hand washing and the use of masks and voluntary quarantine for symptomatic persons could help reduce transmission, while travel-related measures, such as exit screening for persons departing from affected areas, might dampen or delay international spread.

With the emergence of a new pandemic strain, several basic epidemiologic quantities (in addition to the reproductive number) will be unknown, and knowledge of these quantities will be important to the scientifically based design of control measures.

The effectiveness of various potential mitigation strategies is highly dependendent on the precise nature of a novel pandemic influenza virus. It is important to develop principles for what interventions should be implemented when. Specific means of assessing the usefulness of these and other interventions should be developed so that they can be maintained with public support if appropriate, or discontinued if ineffective and disruptive. Plans should also be made to determine who will bear the costs of reduced work attendance, unavailability of childcare, and other likely consequences of such interventions, if they are implemented.



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