Effectiveness and cost-effectiveness of vaccination against pandemic influenza (H1N1) 2009

Abstract

Pandemic (H1N1) 2009 has caused 182 166 confirmed infections and 1799 deaths in more than 150 countries to date (1). Both the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) have declared public health emergencies in response to global circulation of this virus, and the WHO has raised the influenza pandemic alert level from 3 to 6 (2).

As a result of the strain's novelty, most people lack innate immunity to pandemic (H1N1) (3); currently available vaccines do not protect against the virus; and the time needed to manufacture, test, and distribute a matched vaccine is several months (4–5).

In the absence of a matched vaccine, infections and deaths from pandemic (H1N1) will continue globally until a sufficient proportion of the population has developed immunity through infection and recovery, inducing “herd immunity” (population immunity that decreases the effective reproductive rate of the virus below 1, ending the pandemic by epidemiologic definitions [6]). Public health officials were planning to begin vaccination campaigns in mid-October 2009 (7); however, the National Biodefense Science Board, a group of advisors to the U.S. Department of Health and Human Services, recommended moving large-scale vaccine administration to mid-September 2009 (8). Decisions on vaccination timing and distribution are complicated: It is unclear how many individuals would require vaccination to substantially reduce transmission once vaccine is available (some scientists note that the first epidemic wave may in fact already be complete by this time [9]), and it could be expensive to manufacture and administer the vaccine and to treat its side effects.

To help guide policymakers in advising vaccine manufacturers, we developed a model of progression of the 2009 (H1N1) pandemic to determine how vaccination in October or November 2009 would affect the course of the pandemic. We compared the effectiveness and cost-effectiveness of no vaccination, vaccination in mid-October, and vaccination in mid-November.