Safety of influenza A(H1N1)pdm09 vaccines
Overall, the safety information for the pandemic influenza vaccines continues to be reassuring. Other than the association of narcolepsy/cataplexy with an adjuvanted pandemic influenza vaccine in people aged 4–19 years, seen mainly in Finland and Sweden,1 there were no new proven safety signals from passive surveillance systems.
Population-based epidemiological studies on the association of narcolepsy with the adjuvanted pandemic vaccine (Pandemrix) have been completed in Sweden2and Finland. Adhering to the precautionary principle, the European Medical Agency’s Committee for Medicinal Products for Human Use concluded “that the bene-fits of Pandemrix continue to outweigh its risks but that it may only be used in people <20 years of age if the recommended annual seasonal trivalent influenza is not available and if immunization against A(H1N1) is still needed, for instance in people at risk of the complications from infection”. Pandemrix marketing authorization has now expired and this vaccine is no longer in use. Epidemiological studies in other countries in Europe and Canada are under way. Immunological and animal model studies to help elucidate the biological mechanism of the observed association are also in progress.
Although preliminary analyses of active surveillance studies for Guillain-Barré syndrome in the United States, which evaluated both adjuvanted and non-adjuvanted pandemic influenza vaccines, indicated an increased risk, this finding has not been replicated elsewhere to date. Available data do not provide conclusive evidence for this increased risk. Were the risk to be confirmed, it would be much lower than that observed following the 1976 swine influenza vaccination campaign in the United States and would be similar to that observed with use of seasonal influenza vaccines.
GACVS reviewed results from additional epidemiological studies on a possible association between influenza A(H1N1)pdm09 vaccines and certain autoimmune and other clinical syndromes. No major safety concerns appeared, although it was noted that the sample size or methodology of these studies might not have been optimal for establishing causal relations. The Committee acknowledged the need for further analysis in this area.
The safety of pandemic vaccines when administered to pregnant women was reassuring. Data from an observational cohort study in Canada and from a birth and infant health registry in the United States did not point to any safety concerns related to pandemic vaccines among women during gestation or their offspring. Several studies on the safety of pandemic vaccines among pregnant women are still being completed in other regions.
- Statement on narcolepsy and Pandemrix. Geneva, World health Organization, 2011 (http://www.who.int/vaccine_ safety/topics/influenza/pandemic/h1n1_safety_assessing/narcolepsy_statement_Jul2011/en/index.html; accessed January 2012).
- Bardage C et al. Neurological and autoimmune disorders after vaccination against pandemic influenza A (H1N1) with a monovalent adjuvanted vaccine: population based cohort study in Stockholm, Sweden. BMJ, 2011, 343:d5956.