British Swine Flu Vaccine Pandemrix Linked to Narcolepsy in Children

Adolescents who received the A/H1N1 2009 influenza vaccine during the pandemic in England have an increased risk of narcolepsy according to a recent study

The results show-as with previous studies conducted in Finland and Sweden-that the association is not just confined to Scandinavian populations. However, the authors stress that the risks may be overestimated, and they call for longer term monitoring of the children exposed to the vaccine.

In 2009, pandemic influenza A (H1N1) virus spread rapidly, resulting in millions of cases and over 18,000 deaths in over 200 countries. In England the vaccine Pandemrix was introduced in October 2009. By March 2010, around one in four (24 percent) of healthy children aged under 5 and just over a third (37 percent) aged 2-15 in a risk group had been vaccinated.

In August 2010 concerns were raised in Finland and Sweden about a possible association between narcolepsy and Pandemrix. And in 2012, a study from Finland reported a 13-fold increased risk in children and young people aged 4-19.

Yet, a lack of reported cases throughout the countries led to speculation that any possible association might be restricted to these Scandinavian populations.

Narcolepsy is a sleep disorder that causes excessive sleepiness and frequent daytime sleep attacks, often accompanied by sudden muscle weakness triggered by strong emotion (known as cataplexy). To evaluate the risk after vaccination in England, a team of researchers reviewed case notes for 245 children and young people aged 4-18 from sleep centres and child neurology centres across England.

Of these, 75 had narcolepsy (56 with cataplexy) with onset after 1 January 2008. Eleven had been vaccinated before onset of symptoms; seven within six months, according to Science Daily. 

After adjusting for clinical conditions, vaccination at any time was associated with a 14-fold increased risk of narcolepsy, whereas vaccination within six months before onset was associated with a 16-fold increased risk.

In absolute numbers, this means that one in 52,000 to 57,500 doses are associated with narcolepsy, according the authors.

However, these results alone indicate that more research needs to be completed before anything can be determined. 

"Further studies to assess the risk, if any, associated with the other A/H1N1 2009 vaccines used in the pandemic, including those with and without adjuvants, are also needed to inform the use of such vaccines in the event of a future pandemic," authors said.