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VP(R)'s Picks: Influenza B Vaccine and the Limits of ‘Herd’ Protection

Vice-President (Research)'s Picks: Influenza B Vaccine and the Limits of ‘Herd’ Protection


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Living in the same household as someone vaccinated against influenza B is weak protection against the virus. Best to get yourself vaccinated, too, finds an HKU-led study published in Nature Communications.

Children face the highest risk of influenza virus infection and they are important vectors of virus transmission. So if they are vaccinated, shouldn’t that protect other individuals in their household? Previous research has shown that vaccination campaigns targeted at children and other vulnerable individuals do indeed provide “herd protection” in the community, but within households the results have been unclear. A new study led by Professor Benjamin Cowling (School of Public Health) and his team confirms that a different dynamic is at work there.

Using a randomised placebo-controlled trial, they found that living in a household with a child vaccinated against influenza B reduces the risk of infection by only 5% compared with households where children received a placebo vaccine. During the epidemic that was studied, only 10% of all infections were attributable to household transmission. When the scientists pushed the latter figure to 30%, that still only reduced the infection probability by 20% in households with a vaccinated child.

The results compare poorly with getting directly vaccinated yourself, which reduces infection risk by 71%. The study concludes “that the benefits of individual vaccination remain important even when other household members are vaccinated.”

The relative probability of infection for household contacts of vaccinated children, under two vaccination strategies compared with no vaccination strategy. The two strategies are 1: vaccination one child per household and strategy 2: vaccinating all children in the household.

(Image reproduced/adapted from Springer Nature under CC BY 4.0: Tsang T.K., Fang V.J., Ip D.K.M., Perera R.A.P.M, So H.C., Leung G.M., Peiris J.S.M, Cowling B.J. and Cauchemez S., “Indirect protection from vaccinating children against influenza in households”, Nature Communications, 2019, 10, 106, 1-7.)