A meta-analysis of almost 240 studies has challenged assumptions by suggesting that new mothers and obese people have increased risk of severe outcomes and death from in!uenza. In contrast, a greater likelihood of such complications in pregnant women – a group cited as high risk by the NHS – was not shown by the study. 

A research team from McMaster University, Ontario reviewed 239 studies – carried out between 1918 and 2011 and involving over 610,000 people – that looked at risk factors for complications of in!uenza, including developing pneumonia or needing ventilator support admission to hospital, or death.

Results supported the accepted wisdom that risk of complications among the elderly and those with certain comorbidities is raised. But the data also demonstrated that women <4 weeks post partum and people with a BMI >30 also had an elevated risk. In contrast, pregnant women were not found to be at greater risk of complications from ’!u, although the authors acknowledge that this group was not well studied.

In the"UK, about 600 people a year die from a"complication"of seasonal flu – rising to as much as 13,000 during an epidemic. Given the limited eligibility for flu vaccination, the authors point out that priorities for vaccination should be evidence-based. “Policy makers and public health organisations need to recognise the poor quality of evidence that has previously supported decisions on who receives vaccines during an epidemic,” said study lead Dr Dominik Mertz.

“If we can dene the risk groups we can optimally allocate vaccines, and that is particularly important when and if there is vaccine shortage, say during a new pandemic.”