Flu vaccinations protect against ischaemic stroke, according to an analysis of Spanish primary care records.

“Studies have shown that getting flu increases your risk of having a stroke, but research is still being collected on whether getting the flu vaccine can help protect against a stroke,” said study author Dr Francisco de Abajo, from the University of Alcalá, Madrid.

“This observational study suggests that those who have a flu shot have a lower risk of stroke. To determine whether this is due to a protective effect of the vaccine itself or to other factors, more research is needed.”

Researchers matched 14,322 people with ischaemic stroke and 71,610 controls. Adjusting for confounders, flu vaccination reduced the risk of ischaemic stroke by 12 per cent.

The reduction was more marked 15 to 30 days after vaccination (21 per cent) than more than 150 days later (8 per cent reduction). Both differences were statistically significant. 

Flu vaccination produced similar reductions in the risk of cardioembolic (caused by an embolism) and non-cardioembolic (e.g. when an atherosclerotic plaque ruptures) ischaemic stroke. 

However, it did not reduce the risk in patients without vascular risk factors. Inflammation triggered by flu could lead to atherosclerotic plaque rupture but flu jabs produced similar reductions when administered before, during and after the annual season.

Immunisation may trigger a short-term anti-inflammatory effect, which could partly account for the reduction when administered before the annual flu season. 

“These results are yet another reason for people to get their yearly flu shot, especially if they are at an increased risk of stroke,” Dr de Abajo said. 

“To be able to reduce [the] risk of stroke by taking such a simple action is very compelling.”

(Neurology DOI:10.1212/WNL.0000000000201123)