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July 2006 Literature Review Strategies for mitigating an influenza pandemic This is a follow-up report by experts in epidemic modeling to deal with global public health priorities in the event of pandemic influenza. Here the authors examine four issues as follows: Internal or border travel restrictions: This and other analyses are based on data for the US and Great Britain. The results show that border control to restrict passage by 90%, 99% or 99.9% might delay the peak of a US pandemic by 1.5, 3 or 6 weeks, respectively. Their analysis also showed the eliminating travel in and out of the affected areas would delay the spread by up to two weeks. Closing airports for domestic airports had minimal impact. Treatment of Cases: The analysis showed that this would be effective only if there was very rapid treatment, meaning “same day treatment” of 90% of cases. This would reduce the attack rate from 34% to 29% and peak attack rate from 1.9% to 1.6% assuming an antiviral stockpile sufficient for 25% of the population. The urge for early therapy was based on the fact that transmission is at a peak soon after symptoms develop. They also note that effectiveness of antiviral treatment is based on the assumption that there would not be resistant strains with efficient transmissibility similar to that of wild-type virus. They point out that such strains have not been reported to date. Social Distancing: Isolation such as school closings during the peak of the epidemic could reduce the peak attack rate by up to 40%, but this has little impact on the overall attack rate. However, case isolation or household quarantine could have substantial impact. Antiviral prophylaxis to household contacts would reduce the cumulative attack rates, but this would require a stockpile of antivirals sufficient to treat 46-57% of the population which was considered unlikely. Vaccine: Evaluations were based on the assumption that single dose would give 70% protection. Vaccination at a rate of 1% of the population/day would need to begin two months before the pandemic outbreak to have a substantial impact. A delay of four months from the start of the pandemic would mean that the vaccine was available when the pandemic was over. The authors conclude by noting the limitation of their data which would be quite different if the modeling was based on the 1968 or 1957 pandemic rather than the 1918 pandemic. Comment: It should be noted that this is the team that provided one of the initial strategies that received substantial attention including adoption of many of the recommendations by WHO [Ferguson NM, Cummings DA, Cauchemez S, et al. Nature 2005;437:209]. This report seems rather depressing in terms of strategies that are likely to be effective, it is not the quick fix that we have all wanted. Nevertheless, it is somewhat reassuring that the avian influenza spread has slowed in both people and poultry. Literature Review by John G. Barlett, M.D. Professor, Division of Infectious Diseases |
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