An increasing number an influenza experts in the United States are worried that the wave of the swine flu epidemic that has started to hit the country may peak before a vaccine can do much good, a news story in today’s issue of Science explains.
On 15 October, the U.S. government expects to receive the first batches of a vaccine designed to thwart the novel H1N1 virus causing the pandemic. But that is right around the time when many experts now think the spread of the virus may peak in the country. Given that it takes about 2 weeks to build immunity after vaccination and that there will be a limited supply for at least a month or more, the vaccine may have little impact in the United States this fall. “This potential mismatch in timing could significantly diminish the usefulness of vaccination for mitigating the epidemic and could place many at risk of serious disease,” predicted the President’s Council of Advisors on Science and Technology in a report the White House released on 24 August.
On the good news front, many researchers had worried that a vaccine against the novel H1N1 virus would require two doses to build substantial immunity—which would mean further delays in the time required to protect the population as well as twice as much product. But clinical tests of novel H1N1 vaccines published online yesterday by The New England Journal of Medicine show that a single dose can trigger high levels of antibodies in adults. No data are yet available for trials in children, who typically have much less robust immune responses to the seasonal influenza vaccine and require a second dose.
As another paper published yesterday, this one in Science Express, emphasizes yet again, widespread use of a vaccine could have a powerful impact against the H1N1 virus—if it arrived early enough and was widely used. Biostatistician Ira Longini from the University of Washington, Seattle, and his colleagues show that the vaccine would need to reach at least 70% of the population, starting with children first, to significantly impede spread. But Longini, a noted influenza modeler, also suspects that the pandemic now spreading across the United States as children return to school may crest in mid-October.
Longini and others note that this pandemic closely mirrors the one that hit the United States in the fall of 1957. If that occurs, Longini said in an e-mail note, “given the current vaccine production and distribution plan, we will be too late to have any effect on the epidemic.” That is precisely what happened with the vaccine effort in 1957.
With the novel H1N1 pandemic, the vaccine effort began almost immediately after the virus was isolated in late April. “In May, it seemed like we were in good shape with vaccine,” noted Longini. “There seemed to be time.” But now time seems to be running out quickly.