Being vaccinated during pregnancy is effective in preventing infection and hospitalisation in babies, even when the main circulating strain differs from that in the vaccine, research from Public Health England (PHE) has shown.

In 2013/14, analysis of babies born between September and April showed the flu vaccine was 66% effective against laboratory-confirmed cases.

A year later, when the flu season was dominated by a mismatched strain, the vaccine effectiveness fell but was still 50%, the research by PHE scientists and researchers at the London School of Hygiene and Tropical Medicine showed.

The analysis included 37 eligible infants with confirmed influenza in 2013/2014, and 81 in 2014/2015, of which 19% and 25% respectively had vaccinated mothers.

Of those, 30 babies in 2013/14 and 69 babies in 2014/15 had been hospitalised, researchers said.

When looking only at babies infected with the dominant influenza subtype in each season, vaccine effectiveness was even higher at 78% in 2013/14 and against circulating and 60% the following year, the researchers reported in the Journal of Infectious Diseases.

‘Our results over two influenza seasons provide further evidence that giving inactivated influenza vaccine to pregnant women is effective against laboratory-confirmed influenza infection and resulting hospitalizations in their young infants, even in a season with circulation of a drifted strain,’ the researchers concluded.