AS03 adjuvanted pandemic A/H1N1 2009 vaccine increased the risk of narcolepsy in English children and teens, according to the results of a study published in the Feb. 26 issue of BMJ.
The vaccine was introduced in England in October 2009 during the second wave of the A/H1N1 influenza infection. By March 2010, almost a quarter of healthy children aged 5 years or younger and 37% aged 2 to 15 years in a risk group had been vaccinated.
In August 2010, concerns about a possible association between narcolepsy and the vaccine were raised in Finland and Sweden. To evaluate the risk in England, researchers identified cases in those aged 4 to 18 years with onset of narcolepsy after the vaccination since Jan. 1, 2008, and compared them to the proportion of those vaccinated in the country.
Cases from 16 sleep and pediatric centers were identified in July 2011, and clinical information (which included presence of cataplexy and subsequent sleep tests) was extracted from case notes from August 2011 to February 2012. An expert panel confirmed the diagnoses.
Of the 245 identified children, 75 had narcolepsy after Jan. 1, 2008; 66 were definite cases and the remaining nine were considered probable. Eleven of the definite cases had been vaccinated before onset; six within 3 months, one within 3-6 months, and four between 7-14 months.
In those with a diagnosis by July 2011, the odds ratio was 14.4 (95% CI, 4.3-48.5) for vaccination at any time before onset, showing a significantly increased risk of narcolepsy in children who received the vaccine, researchers reported. This number was also consistent with the 13-fold increased risk reported from a Finland retrospective cohort study.
“While further use of the … vaccine for prevention of seasonal A/H1N1 2009 seems unlikely, our findings have implications for the future licensure and use of AS03 adjuvanted pandemic vaccines containing different subtypes, such as H5 or H9,” the researchers concluded.