Immunisation is one of the most effective ways to reduce avoidable morbidity and mortality during influenza pandemics. The current national pandemic plan states that “the Australian Government aims to vaccinate … a large enough proportion of the Australian population to slow transmission.”1 Although the risk of adverse events following influenza (AEFI) vaccination is low, when rapidly applied to a national population the absolute number of such incidents may be substantial and concentrated in a short time period. AEFI can generate considerable media and public attention, and erode trust in vaccination.2 Experience suggests disproportionate public attention will be brought to named cases of severe adverse responses, despite the much larger number of non-identifiable lives saved by immunisation.
Applying the same risk profile as seasonal influenza vaccination published in the Australian Immunisation Handbook, it would be expected that a single dose regime using the 21 million doses of pandemic (H1N1) 2009 influenza vaccine purchased by the Australian Government will lead to between one and two million persons with mild or local adverse reactions such as fever or myalgia.3 Children with more severe responses will require further care and related news reports may provoke public anxiety and excess demand on both community and hospital medical care, as seen in response to child deaths from influenza in 2007.4 With an incidence of one to two cases per million vaccinations,3 there could be as many as 20 incident cases of Guillain-Barré Syndrome and a similar number of acute anaphylactic reactions. It is also possible that there may be one or two cases of life-threatening anaphylaxis, and further cases of rare side effects that only become visible in very large programs; as occurred during the 1976 US national immunisation campaign against a possible pandemic ‘swine flu’ strain, leading to withdrawal of the program.5
Consistent, evidence-based messages regarding AEFI need to be prepared and disseminated before, during and after the mass immunisation program to maintain public confidence in the program. Doctors, health workers and immunisation staff need to be aware of the absolute numbers of AEFI that might be expected, how to manage them, and the need to maintain routine good immunisation practice during rapid roll-out of the program.