Does the Flu Vaccine Really Work?

The science on flu vaccines and winter illness

Every fall, there’s a big push to encourage people to get their flu shots before winter. It’s seen as one of the best ways to reduce the risk of flu – and the likelihood of hospitalization or death as a result. But many Americans don’t heed the call – with only around 40% of adults and 63% of children getting the vaccination each year.

There are a few reasons for ignoring vaccination advice. Some don’t believe the flu is a big deal, some buy into anti-vax misinformation about the dangers of vaccines and some have difficulty accessing or affording the shot. Some simply can’t be bothered and others don’t believe the vaccine works.

But does it? As always, when it comes to disease, the answer is not as simple as it seems. The flu shot doesn’t offer 100% protection against the flu, but it does reduce the risk and protect the wider population against the worst effects of the virus.

Understanding the flu shot

Vaccinations work by introducing a tiny amount of a disease into the body, which produces antibodies in response. Later, if the person is exposed to the same disease, the antibodies are primed to fight off the virus and prevent illness. If the person does develop the illness after a vaccination, it’s likely to be less severe.

For some diseases – like measles, mumps and polio – one or two shots can provide protection for decades. The flu shot is slightly different. Because there are multiple strains of the flu circulating at any one time, the flu vaccine is different every year. It’s tailored to protect against the three or four flu strains research shows will be most common in the upcoming season. That’s why doctors recommend getting a flu shot every year.

Exactly how effective is it?

CDC data show that in years where the vaccine closely matches current flu viruses, the shot reduces the risk of catching the flu by 40-60%. It can also reduce the severity of the virus, preventing more serious effects. Of course, if it doesn’t include significant circulating flu strains this number can drop.

By preventing influenza infections, flu shots also prevent flow-on effects like doctor’s visits, hospital admissions, serious secondary illnesses and even deaths. During the 2018-19 season alone, around 3,500 flu-related deaths were prevented by the flu shot.

But because every person has a different health profile, the effectiveness of the vaccine is different for each. Factors like age, underlying health conditions and pregnancy can all change how well it works.

Different age, different result

The flu shot works best for healthy adults. That’s not to say that other people don’t see a benefit, it’s just that effectiveness declines for certain age groups. It’s less helpful for children under the age of two, with effectiveness increasing with as they grow older.

Because natural immunity declines with old age, the shot is also slightly less effective for older people. But this group shouldn’t be tempted to skip the shot – older people also face higher risks if they do catch the flu. Between 70-85% of flu-related deaths and 50-70% of hospitalizations occur in the 65+ age-group. That’s why many physicians offer a special high-dose shot for older people, with around four times the intensity of a regular vaccine.

Underlying health conditions and immunity

Vaccines trigger your natural immune system to fight the virus. If your immunity is compromised by chronic illness or underlying health conditions, it won’t be able to react as strongly – which means the vaccine will be less effective in preventing the flu. This group, which includes people with a history of cancer, heart disease, diabetes or asthma, is also more likely to have serious complications as a result of the flu.

Of course, less effective doesn’t mean useless. The flu vaccine can still reduce the risk of serious illness and hospitalization in people with health conditions by up to 70%, according to CDC estimates.

Pregnancy and the impact of flu

Pregnant women and those who have recently given birth are also at risk of serious flu-related illness – and the vaccine may be less effective for this group as a result of changes to the immune system during pregnancy. Serious complications during pregnancy can also put the fetus at risk, as fevers and dehydration can cause neural tube defects and other conditions in developing babies.

For this reason, pregnant women are advised to get the flu shot during pregnancy. Research shows that getting the shot reduces the risk of hospitalization by around 40% for pregnant women, and also passes on antibodies to the baby, giving it protection for a few months after birth.

Shot or not?

The flu vaccine isn’t a magic bullet that prevents all influenza infections. Even in a good year, it only reduces the risk of catching the flu by 40-60%, and this rate is lower for at-risk groups like young babies, the elderly, pregnant women and people with underlying health conditions.

But getting the shot is still a better bet – especially if you fit into one of the at-risk categories. The vaccine may not prevent all illness, but it has been shown to lessen the severity of symptoms and reduce the risk of hospitalization or death. That’s got to be worth a shot.