Babies with older siblings more likely to be hospitalised with the flu

Children under two years are more likely to end up in hospital with the flu if they have an older sibling, a UK study has found.

Flu can be a “serious infection in very young children”, according to lead researcher, Dr Pia Hardelid from the UCL Great Ormond Street Institute of Child Health, UK.

Dr Brian Oliver from the University of Technology Sydney told the Australian Science Media Centre that although it isn’t possible to immunise babies under six months old, there is a way to help keep them healthy.

“If you want to protect children under six months from having a serious influenza infection you need to make sure that other children in the family have been immunised,” suggested Oliver.

The researchers studied almost all children born in Scotland between October 2007 and April 2015 – around 400,000 in total. They looked through hospital and lab data to find out what kids who had had the flu also had in common. 

Babies less than half a year old with older siblings were more than twice as likely to be hospitalised with the flu than babies without older siblings, the researchers found.

For babies with just one older sibling, there was one extra hospitalisation per 1,000 children, but if they had two older siblings, it was an extra two hospitalisations per 1,000 children. 

Almost half of flu hospital admissions in babies under six months old could be explained by older siblings, said the authors.

“Children are very effective spreaders of respiratory viruses like flu,” explained Hardelid. “Older siblings pose a risk of serious infection for their baby sisters and brothers.”

The study also found babies who were very young at the start of the flu season also had a higher risk.

“There is not much parents can do about the time of year their baby is born, but women can also help reduce the risk of serious flu for their newborns by [getting vaccinated] when they are still pregnant,” suggested Hardelid.

Having others immunised can help protect “all at-risk populations; for example, the ill, the elderly”, explained Oliver.

“It’s better to stop exposure to influenza,” he concluded.

This article also appears in Science Deadline, a weekly email newsletter from the Australian Science Media Centre.