The maps and charts above offer two scenarios for spread of the H1N1 virus, projected to Day 100 of the epidemic: Top, if the virus is permitted to spread without mitigation; and bottom, the prevalence if at least 70% of the nation's population is vaccinated, with children receiving the highest priority for vaccines. [Image courtesy of Ira Longini]
Vaccinating at least 70% of U.S. residents against the H1N1 virus—very soon—could limit spread of the disease to levels usually seen in a mild seasonal flu epidemic, researchers report.
In the optimal scenario, children would receive the vaccine first, no later than this month, according to Yang Yang of the Fred Hutchinson Cancer Research Center and colleagues. Their research is being published online today by Science, at the Science Express website.
The researchers analyzed recent data from the ongoing pandemic to provide up-to-date estimates of its impact. Based on reported cases in the United States, they estimate that the rate of transmissions within households puts the 2009 H1N1 virus in the higher range of transmissibility compared to past seasonal and pandemic strains.
Children are a particularly important part of the picture, with each infected child potentially able to infect two to three others, roughly every three days.
The authors used a computer model to simulate how vaccination would affect the U.S. epidemic this fall, under different circumstances, involving, for example, who receives the vaccine first, when they receive it, and how quickly the vaccine is able to generate a protective immune response.
They conclude that if the vaccine were available soon enough, a vaccination program that reached 70% of the population, targeting children first, could effectively mitigate the epidemic.
Although the study suggests that the vaccine should be administered by mid-September to be maximally effective, the vaccine probably wonÕt be distributed until October, co-author Ira Longini of the Fred Hutchinson Cancer Research Center and the University of Washington told the Science podcast. Vaccination would still be extremely important, however.
"Even if we're late with vaccination, this virus is probably going to be with us for many years to come in various forms, maybe as much as a couple of decades. So, I think that vaccination is very important, to try to at least get people primed and start building up population-level protection against this virus," he said.
View movie clip 1 : Model simulation showing how the 2009 H1N1 virus may spread in the United States if there is no vaccination intervention (top), as compared to a vaccination effort that covers 70% of the population with no particular age or risk group targeted (bottom). In the top simulation, the virus is widespread by day 70 with the epidemic peaking on day 103. In the bottom panel, the population is vaccinated starting on day 30 and ending on day 135 when 70% of the population is covered. The epidemic is well-mitigated with spread equivalent to a mild seasonal influenza epidemic. [Video courtesy of Ira Longini]
View movie clip 2 : Model simulation showing how the 2009 H1N1 virus may spread in the United States if there is no vaccination intervention (top), as compared to a vaccination effort that covers 70% of the population, with children targeted first (bottom). Without mitigation, the virus is widespread by day 70 with the epidemic peaking on day 103. In the bottom panel, the 70% of children are vaccinated between days 30 and 61, followed by 70% of adults being vaccinated between days 61 and 135. The epidemic is well-mitigated with little spread. [Video courtesy of Ira Longini]