The best way to contain a flu epidemic is to vaccinate children, not the elderly, which is the current practice, a Yale School of Medicine researcher reports in Proceedings of the National Academy of Sciences.

The lead author, Alison Galvani, assistant professor in the Department of Epidemiology & Public Health, examined her data in the context of a population game known as the "Nash strategy." Under this strategy devised by Nobel Prize winning economist John Nash, self-interest usually trumps the greater good.

Galvani asked about 600 employees at a New Jersey university-half 65 and over and half under 65-about their attitude towards flu shots. The Centers for Disease Control defines the target group for vaccination as 65 and over. She found that people 65 and over were more likely to be vaccinated than other adults.

However, Galvani said, it is children who generally carry the flu virus into the home and adults then carry the flu into the workplace. The elderly are, though, at greater risk of dying if they contract the flu.

"If people follow the 'Nash' strategy, children will be vaccinated less often than the elderly," Galvani said. "This presents an obstacle to optimal control of influenza for the community."

She also found people overestimate their chances of catching the flu and the length of time the disease is contagious and underestimate the effectiveness and duration of the vaccine. The respondents did correctly estimate the length of time they would suffer symptoms-between four and five days.

In contrast to the Nash strategy is the utilitarian strategy, which relies on "herd immunity." The idea is that when a large proportion of a group is immune to a disease, there are fewer people to pass it along and the disease rapidly disappears. Galvani said the flu would be virtually eliminated if most young persons were vaccinated.

The Nash and utilitarian strategies produce the same results in a pandemic.

"During pandemics the young are responsible for most transmission, but they also experience disproportionately more severe infection," Galvani said. "Hence, individual and community incentives are in greater accord than for epidemic influenza."

Proceedings of the National Academy of Sciences (PNAS)104: 5692-5697 (March 16, 2007)