An aggressive vaccination program that first targets children and ultimately reaches 70% of the U.S. population would mitigate pandemic influenza H1N1 that is expected this fall, according to computer modeling and analysis of observational studies conducted by researchers at the Vaccine and Infectious Disease Institute (VIDI) at Fred Hutchinson Cancer Research Center.
Published in the Sept. 11 issue of Science Express, the early online edition of the journal Science, the study – which includes the first estimate of the transmissibility of pandemic H1N1 influenza in schools – recommends that 70% of children ages 6 months to 18 years be vaccinated first, as well as members of high-risk groups as identified by the U.S. Centers for Disease Control and Prevention. These groups include health care and emergency services personnel and those at risk for medical complications from pandemic H1N1 illness such as persons with chronic health disorders and compromised immune systems. Two doses of vaccine, delivered 3 weeks apart, may be needed to confer adequate protection to the virus.
Corresponding author Ira Longini, PhD, and colleagues emphasized that a combination of factors – the availability of an effective vaccine to protect people against pandemic H1N1, coupled with the timing of the outbreak – will determine how quickly the epidemic can be slowed. The researchers estimate that to bring the epidemic under control aggressive vaccination of the population must begin at least a month before the epidemic peak, concentrating on children as much as possible.
“Our estimates of pandemic H1N1 in households, schools and in the community places this virus in the higher range of transmissibility,” Yang Yang, PhD, first author of the paper and a staff scientist at VIDI, said in a press release.
Although social distancing and the use of antiviral medicines can be partially effective at slowing pandemic flu spread, vaccination remains the most effective means of pandemic influenza control, the authors conclude. From a cost effectiveness measure, vaccination remains the most effective, while closing schools and other social gathering places is the least cost effective.
Vaccination increases population-level immunity and lowers the effective reproductive number of the virus, which results in two main effects: slowing the spread of infection and reducing the height of the epidemic peak; and reducing the overall illness attack rate, hospitalizations and mortality.