An article published Online First and in the December edition of The Lancet Infectious Diseases discusses the benefits and disadvantages of vaccination for children against seasonal flu. It reports that infection with “seasonal” influenza A could in fact benefit children by giving them improved immunity against pandemic strains such as the current swine flu H1N1 strain. Therefore, vaccinating children aged six months to five years against seasonal flu, as is recommended in some countries, could be disadvantageous to these children. The article discussing this controversial theory is the work of Dr Guus Rimmelzwaan, Erasmus Medical Center, Rotterdam, Netherlands, and colleagues. In an associated comment, Drs Terho Heikkinen and Ville Peltola, Turku University Hospital, Turku, Finland, disagree. They explain that preventing children from catching seasonal flu is a definite benefit of vaccination which far outweighs the theoretical risk suggested by Rimmelzwaan and colleagues.
It has been proven, primarily in animals, that infection with influenza A viruses can bring protective immunity to influenza A viruses of other unrelated subtypes. Rimmelzwaan and colleagues remark: “This so-called heterosubtypic immunity does not provide full protection, but can limit virus replication and reduce morbidity and mortality of the host.”
They continue by saying that this type of immunity might be applicable to human beings when a new subtype of influenza A virus is introduced into the population, such as the new influenza A H1N1 virus (swine flu) responsible for the current pandemic. This could also be the case for potential future pandemics that may be caused by avian flu subtypes. Avian flu in humans is still very rare. However in those infected, it does cause high levels of mortality.
The authors explain: “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 present pandemic could originate an exceptional chance to investigate heterosubtypic immunity. According to the authors, close monitoring of admissions to hospital and mortality rates could allow a comparision of records of infants that have received annual influenza vaccination since birth with unvaccinated age-matched children. This might offer information on the potential downside of yearly influenza vaccination.
Rimmelzwaan and colleagues write in conclusion: “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.”
Fundamentally, Rimmelzwaan and colleagues continue by saying that they fully support the forthcoming vaccination programme against H1N1 influenza. It will reduce severe disease and mortality in all age groups.
They remark: “Use of these pandemic influenza vaccines will over-ride the theoretical issues associated with yearly vaccination against seasonal influenza.”
In a related comment, Heikkinen and Peltola observe 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 do concur with Rimmelzwaan and colleagues on one point which is the need for further effective influenza vaccines that would also generate broader immune responses.
Nevertheless, they write in conclusion: “Public health decisions should be based on the best clinical evidence available. There is ample evidence for the great burden of influenza in young children, and this burden appears during every influenza season. By contrast, there is no clinical evidence that vaccinating children against influenza would prevent the induction of heterosubtypic immunity and thereby be disadvantageous to children in the long run. 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.”
“Yearly influenza vaccinations: a double-edged sword?”
Rogier Bodewes, Joost H C M Kreijtz, Guus F Rimmelzwaan
Written by Stephanie Brunner (B.A.)