Seasonal flu vaccination in children may hinder immunity to pandemic strains
MedWire News: Vaccinating all young children against seasonal influenza A, as proposed in some Western countries including the USA, could, in theory, prevent them from developing immunity against pandemic strains such as N1H1 (swine flu), experts argue.
In a ‘personal view’ article published in The Lancet Infectious Diseases, Guus Rimmelzwaan (Erasmus Medical Center, Rotterdam, The Netherlands) and colleagues explain that the results of animal studies suggest that infection with influenza A viruses can induce protective immunity to influenza A viruses of other unrelated subtypes.
“This so-called heterosubtypic immunity does not provide full protection, but can limit virus replication and reduce morbidity and mortality of the host,” they say.
They add that this type of immunity could potentially occur in humans when a new subtype of influenza A virus starts to circulate in the population, such as the H1N1 virus that is responsible for the current swine flu pandemic. It may also be protective against avian flu subtypes, which are still rare in humans but are associated with high mortality rates in those infected.
“Preventing infection with seasonal influenza viruses by vaccination might prevent the induction of heterosubtypic immunity to pandemic strains, which might be a disadvantage to immunologically naive people, such as infants,” the authors explain.
They say that during the current pandemic, comparison of hospital admissions and mortality rates among infants who have received annual influenza vaccination since birth with those in unvaccinated age-matched children might provide valuable information on the potential drawbacks of yearly influenza vaccination.
Rimmelzwaan and colleagues conclude: “The development and use of vaccines that can induce broad protective immunity might be a solution for these potential problems and we think this is a priority.”
Nevertheless, they add that they fully support the current vaccination programs against H1N1 influenza, which they say will reduce severe disease and mortality in all age groups.
In an accompanying commentary, Terho Heikkinen and Ville Peltola from Turku University Hospital in Finland say that “the results of experimental animal studies can never be extrapolated directly to human beings, let alone form the basis of any vaccination policy”.
They add: “While waiting for improved influenza vaccines, the simple question is should we let young children suffer from a severe and potentially lethal but easily preventable illness, just because there is a theoretical possibility that withholding vaccination might result in a slightly less severe illness sometime in the future? We believe that the answer to this question is a simple one.”
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By Mark Cowen