Half-Dose Influenza Vaccine:  Stretching the Supply or Wasting It?

Seasonal influenza is responsible for 200 000 to 400 000 hospitalizations and 20 000 to 40 000 deaths annually in the United States.¹ At present, the cornerstone of influenza control is vaccination. Groups recommended by the Advising Committee on Immunization Practices (ACIP) to be vaccinated yearly include all adults older than 50 years, children aged 6 to 23 months, chronically ill persons, and health care workers. Although an effective live attenuated vaccine is approved for persons aged 5 to 49 years, trivalent inactivated vaccine (TIV) remains the primary method of vaccination for the majority of at-risk populations. The production of adequate supplies of yearly influenza vaccine is challenging for a number of reasons, including the need to anticipate new circulating strains in advance, adaptation of new variants for growth in embryonated hens' eggs, and an expanding target population. These issues are further complicated by the exodus of US vaccine manufacturers. In 1967, 26 companies made vaccines for the US market; today, few remain.² Not surprisingly, 2 major interruptions with influenza vaccine production have occurred in the last 8 years. In 2000-2001, a significant delay in vaccine production occurred, and although the full complement of vaccine was eventually distributed, a considerable disruption in care resulted. During 2004-2005, vaccine lots produced at a Chiron Corp production facility had evidence of contamination with the bacteria Serratia marcescens. The plant was closed temporarily, resulting in a loss of nearly half the planned one hundred million doses for US distribution. As a result, healthy persons were asked to forgo vaccination and high-risk individuals were strategically prioritized.