Influenza can help trigger heart attacks and may account for a 35 percent to 50 percent rise in heart attack deaths during flu season, British researchers reported on Monday.

While a flu vaccine can prevent these deaths, fewer than half of the most vulnerable heart patients in Britain actually get a flu vaccine every year, however, they said.

We believe influenza vaccination should be encouraged wherever indicated, especially in those people with existing cardiovascular disease, Charlotte Warren-Gash of University College London and colleagues wrote in the journal Lancet Infectious Diseases.

Further evidence is needed on the effectiveness of influenza vaccines to reduce the risk of cardiac events in people without established vascular disease.

Warren-Gash and colleagues reviewed 39 studies conducted between 1932 and 2008 on the potential links between flu and heart deaths.

All the studies that covered entire populations showed a rise in deaths due to heart disease or heart attacks when influenza viruses were circulating, they found.

Seasonal influenza kills about 250,000 to 500,000 people a year, a figure that experts came up with by carefully monitoring confirmed flu deaths in a small area, counting excess deaths during influenza season over large populations, and consolidating both calculations.

Warren-Gash's team found the proportion of excess influenza deaths that were due to heart disease ranged from 35 percent to 50 percent.

Four out of eight studies showed people who were vaccinated from seasonal influenza were less likely to have a heart attack they found.

But in Britain, only 47 percent of people with chronic heart disease, asthma, diabetes or other conditions who are supposed to get a flu shot did last year.

Countries now are gearing up to vaccinate hundreds of millions of people against the pandemic H1N1 swine flu and people with chronic heart disease are at the top of the list of those who should get one.

United kingdom Medicine