Children who are born prematurely have an over four times greater risk of severe flu complications, despite not being considered a high-risk group by global guidelines.

In keeping with existing guidelines the systematic review and meta-analysis of 27 studies involving 14086 children also identified children with neurological disorders (OR 4.62, 95% CI 2.82-7.55), sickle cell disease (OR 3.46, 1.63-7.37), immunosuppression (OR 2.39, 1.24-4.61) and diabetes (OR 2.34, 1.20-4.58) at greater risk of flu complications.

The analysis published in Lancet Respiratory Medicine by Dr Kay Wang from the University of Oxford in the UK and colleagues also found the presence of multiple medical conditions significantly increased the risk of hospital admission from 52% (one condition) to 74% (>1 condition).

Surprisingly the authors did not find any significant association between admission to hospital for influenza and asthma or other respiratory conditions, obesity, heart conditions or cancer.

However writing in an accompanying editorial Harish Nair from the University of Edinburgh in the UK, and Marc-Alain Widdowson from the Centers for Disease Control and Protection in the US said this particular finding should be interpreted with caution as the authors measured the risk of admission to hospital among children already seeking care.

“If respiratory disease or asthma is already associated with seeking ambulatory care for influenza, then these characteristics might not have been identified as risk factors,” they wrote.

 They also advised caution on the prematurity finding, as five of the seven studies in the analysis did not define prematurity by gestational age.

However, if confirmed, the finding could have “major policy implications” as 11% (15 million) of the world’s babies are born pre-term, they said.

“Current WHO guidelines for seasonal influenza vaccination do not include preterm babies in the list of high-risk groups, but perhaps the new findings support their eventual inclusion,” they wrote.

However protection of these susceptible children comes with challenges, they noted.

“Children cannot be vaccinated before age 6 months; inactivated vaccines are poorly immunogenic in young children, necessitating two doses, and live, attenuated influenza vaccines are only recommended in children aged 2 years or older”.