Dear parents, please-take-note! A study has recently warned that small children under two years of age, especially six months old, are at greater risk of serious illness from influenza if they have an older sibling.
According to researchers, babies and young children can be better protected if parents take up the opportunity to get older siblings vaccinated.
Flu can be serious in very young children because it can cause lung infections and breathing difficulties.
It can also cause a very high fever, leading to fits called febrile convulsions.
Lead researcher Dr Pia Hardelid, from the UCL Great Ormond Street Institute of Child Health in London said, "Flu can be a serious infection in very young children but at the moment there is no vaccine approved for babies under six months. This means we need to look at other ways to minimise the risk of infection."
They studied almost all children born in Scotland between October 2007 and April 2015, about 400,000 in total.
They used anonymised hospital admissions and laboratory data to find out which children had a record of a positive laboratory test result for flu and compared this with other routinely collected information, such as month of birth, whether they were premature or had other health conditions, and whether the children had older siblings.
The results showed that children under six months old with older siblings were more than twice as likely to be admitted to hospital with flu than children who did not have older siblings.
For those with two older siblings, there were two extra hospital admissions for every 1,000 children.
The risk was also higher for babies born between July and December, who would be very young at the start of the flu season.
Our study suggests that older siblings pose a risk of serious infection for their baby sisters and brothers.
The research is published in the European Respiratory Journal.