Strategies for pandemic and seasonal influenza vaccination of schoolchildren in the United States

Abstract

Vaccinating school-aged children against influenza can reduce age-specific and population-level illness attack rates. Using a stochastic simulation model of influenza transmission, the authors assessed strategies for vaccinating children in the United States, varying the vaccine type, coverage level, and reproductive number R (average number of secondary cases produced by a typical primary case). Results indicated that vaccinating children can substantially reduce population-level illness attack rates over a wide range of scenarios. The greatest absolute reduction in influenza illness cases per season occurred at R values ranging from 1.2 to 1.6 for a given vaccine coverage level. The indirect, total, and overall effects of vaccinating children were strong when transmission intensity was low to intermediate. The indirect effects declined rapidly as transmission intensity increased. In a mild influenza season (R = 1.1), approximately 19 million influenza cases could be prevented by vaccinating 70% of children. At most, nearly 100 million cases of influenza illness could be prevented, depending on the proportion of children vaccinated and the transmission intensity. Given the current worldwide threat of novel influenza A (H1N1), with an estimated R of 1.4-1.6, health officials should consider strategies for vaccinating children against novel influenza A (H1N1) as well as seasonal influenza.

Figure 1.

Baseline influenza illness attack rates (AR, %) and number of cases (millions) based on the model and a US population of 305.5 million people for reproductive number (R) values ranging from 1.1 to 2.4.

Figure 2.

Influenza illness attack rates, at baseline and after 70% of children are vaccinated, for a range of values of the reproductive number (R) for both homologous and heterologous vaccine.

Figure 3.

Age-specific influenza illness attack rates for adults and children, at baseline and after 70% of children are vaccinated, for a range of values of the reproductive number (R) when the vaccine is homologous.

Figure 4.

Indirect, overall, and total vaccine effects (VE) for adults and children when 70% of children are vaccinated with live, attenuated vaccine for a range of values of the reproductive number (R) when the vaccine is homologous.

Figure 5.

Indirect vaccine effects (VE) for adults after vaccinating children with influenza vaccine for a range of values of the reproductive number (R) when the vaccine is homologous.