The immune system generally weakens as we get older, not only leaving people more vulnerable to infection but also reducing their ability to respond to vaccination.

Now, a new study monitoring nearly 4,000 people has found that giving people aged 65 and older a dose four times larger than the standard flu vaccine boosts the amount of antibodies in their blood to levels considered protective against the flu, more so than the standard flu vaccine does.

The higher dose of vaccine generally resulted in between 30 percent and 80 percent more antibodies against flu, long considered a good measure of protection, according to researchers at the University of Rochester in the US.

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Some previous studies had questioned the effectiveness of the flu vaccine in older adults, but health experts say that it’s a worthwhile, even life-saving, measure.

’Without doubt, the influenza vaccine as it is today is beneficial for everyone, including older adults, and we strongly encourage every older person, and every person with a chronic illness, to get vaccinated,’ said researcher professor Dr Ann Falsey.

’However, older people generally don’t respond to vaccines as well as young healthy adults and therefore, there is much room for improvement. The goal is to increase immune response in older adults, since this is one of the populations most at risk for becoming seriously ill or dying from influenza.’

The conventional flu vaccine is a combination of three circulating strains of flu, designed to evoke an immune response to protect a person against common types of flu.

In the study, doctors compared the immune response brought about from a traditional flu vaccine compared to that from a vaccine shot containing four times as much of each strain of flu.

Scientists checked the levels of antibodies in the blood of the participants one month later. They found that the large-dose vaccine increased the number of flu antibodies on average from about 30 to 80 percent. The level of such antibodies in the blood has long been considered a good gauge of how protected people are against the flu.

However, a greater percentage of people who received the high-dose vaccine had the typical side effects associated with the flu shot, including redness, swelling, and pain at the site of the injection. The symptoms generally did not last longer than three days.