Published: 19-11-2015 11:02 | Updated: 19-11-2015 11:05

Influenza vaccine had no affect on fetal mortality risk

A fresh study from Karolinska Institutet can quell any fears there might be of an increased risk of fetal and neonatal mortality for mothers who have been inoculated with the Pandemrix vaccine for H1N1-influensa while pregnant. The results are published in British Medical Journal (BMJ).

A large portion of the Swedish population had themselves vaccinated against the new H1N1-influensan (also known as swine flu) in connection with the 2009-2010 outbreak. Since then, there has been much debate surrounding the Pandemrix vaccine, especially after research had shown that it increases the risk of narcolepsy in children and adolescents and young adults.

Dr Jonas F. Ludvigsson, paediatrician and professor at the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet, therefore decided with his colleagues to examine if the vaccination of pregnant women could affect fetuses and newborn babies.

A study published in 2013 in the European Journal of Epidemiology gave reassurances on the supposed increased risk of low birth-weight, stunted growth or premature birth; these results have now been complemented by this present study in BMJ showing that vaccination with Pandemrix during pregnancy has no effect on the risk of fetal/neonatal mortality either.

No higher risk

The researchers analysed a total of 275,500 pregnancies, 41,183 of which had been exposed to Pandemrix. During the follow-up period, there were 1,172 stillbirths, 380 neonatal deaths (0-6 days after birth) and 706 infant deaths (7 days up to 4.6 years).

This, say the team, means that there is no higher risk of foetal/infant death for women vaccinated while pregnant. This same result was found on comparing fetuses exposed to the vaccine with their unvaccinated siblings.

The study was financed with grants from the Swedish Research Council and the Swedish Research Council for Health, Working Life and Welfare (FORTE). Jonas Ludvigsson is also a paediatrician at Örebro University Hospital.


Maternal vaccination against H1N1 influenza and offspring mortality: population based cohort study and sibling design
Jonas F. Ludvigsson, Peter Ström, Cecilia Lundholm, Sven Cnattingius, Anders Ekbom, Åke Örtqvist, Nils Feltelius, Fredrik Granath, Olof Stephansson
BMJ, online 16 November 2015, doi: