Flu vaccine cuts risk of blood clots on long flights

Air passengers worried about the risk of "economy class syndrome" could protect themselves by having a flu jab, new research suggests.

Vaccinations against influenza significantly reduce the chances of developing dangerous blood clots in the veins, a study has found.

Researchers found that the jabs reduced the likelihood of developing a venous thrombotic embolism (VTE) by more than a quarter – 26 per cent.

For women on the Pill, the risk was cut by as much as 59 per cent.

One type of VTE is deep vein thrombosis, or DVT – commonly known as "economy class syndrome". It usually occurs in the legs and is often associated with long flights.

Sometimes a leg clot can break away and travel in the bloodstream to the lungs, producing a life-threatening pulmonary embolism.

French scientists conducting the Farive study compared a group of 727 VTE patients with an equal number of men and women who had no history of thrombosis. The average age of those taking part was 52.

Patients were questioned about VTE risk factors, including pregnancy, use of the contraceptive Pill or hormone replacement therapy, recent injury or surgery, prolonged periods of immobilisation, or travel lasting more than five hours.

The researchers also noted whether participants had received a flu jab in the previous year. Overall, the risk of suffering a VTE was found to be 26 per cent less for patients who had been given an influenza shot.

For people younger than 52, the level of protection was 48 per cent. Women under the age of 51 had their odds of developing a VTE reduced by 50 per cent after a flu jab, while those on the Pill were 59 per cent less at risk.

The protective effect of vaccination was the same for both DVT and pulmonary embolism.

Findings from the research were presented yesterday at the American Heart Association's Scientific Sessions meeting in New Orleans.

Dr Joseph Emmerich, the study's leader from the University Paris Descartes, said: "Our study suggests for the first time that vaccination against influenza may reduce the risk of venous thrombotic embolism." The vascular medicine specialist added: "This protective effect was more pronounced before the age of 52 years."

The reason why flu jabs help to prevent vein clots is unclear, he said, but one theory is that they could stop infection thickening the blood or dampen down harmful inflammation.

"Infections in general increase blood viscosity, and systemic inflammatory reactions to infectious agents can themselves trigger a thrombotic process," said Dr Emmerich.

"However, influenza vaccination might lower the risk of thrombosis in other ways, as suggested by the even distribution of VTE events across the 12 months of the year in both vaccinated and unvaccinated cases in our study."

Further work was needed to confirm the relationship between influenza vaccination and VTE and to explore the underlying mechanisms, he said.

He suggested that flu jabs could be recommended after a first VTE event.