How effective is the flu shot?

Every fall, as Americans roll up their sleeves to get their vaccine against influenza, a question remains: how effective will the vaccine be? this year? The answer, according to experts, is that we can’t know for sure, but even so, the vaccine is safe and your best protection against severe flu.

Why does the efficiency fluctuate every year?

If you look at the numbers on the effectiveness of the flu vaccine in protecting Americans against the flu over the past few decades, there is a pretty wide range, ranging from 19% in 2014-15 to 60% in 2010-11. (These numbers mean that, for example, in 2010-11, 60% fewer healthy adults who are vaccinated contracted the flu compared to those who were not vaccinated.)

Why the gap? It is about methodically trying to predict the future, according to Richard Webby, Ph.D.., influenza expert in the infectious disease department at St. Jude Children’s Research Hospital. He explains that the World Health Organization (WHO) has a network of around 148 laboratories in 120 countries, which collect samples from people with flu-like symptoms during their typical flu season. Then they analyze the samples and analyze the data. “This group meets several times a year and asks a pretty simple question: Looking at the vaccine strains we have now, how closely do these match up with the strains that we think are going to predominate in six months? he explains.

Armed with this information, each country produces the vaccines it believes are best for its people. In the USA, all vaccines this year are quadrivalent, which means they protect against four different strains of influenza, two types of influenza A and two of influenza B, explains Ada D. Stewart, MD, a family physician with Cooperative Health in Columbia, SC, and Chairman of the Board of Directors of the American Academy of Family Physicians. When this match is good, it reduces the risk of disease for healthy adults somewhere between 40 and 60 percent, According to the CDC.

But sometimes, as we recently discovered with COVID, new strains can surprise us. “When we design the vaccines, the flu may still be present in another hemisphere, and when it comes back, it may have taken a slightly different direction than expected, so we don’t get that perfect match between what’s in there. the vaccine and the strains in circulation, ”says Dr. Webby.

What will happen this year?

Last year, through hand washing, social distancing, and wearing masks, we had one of the mildest flu seasons in recent history. There were significantly fewer illnesses, hospitalizations and deaths (approximately 700 people deaths from influenza, up from 22,000 the previous year). “I can tell you that as a practicing family physician, I have had zero tested positive for the flu last year, ”says Dr. Stewart. In addition to all the security precautions and lockdowns from the COVID pandemic, there was also a registration number influenza vaccines distributed last season (about 55% of adults were vaccinated against influenza, up from 48% the previous year).

It was great news for last year, but it has mixed meanings for this year. While Americans are certainly more used to staying home and staying safe when feeling sick, last year’s minimal flu season means researchers had less data to use to create the vaccine against the disease. flu this year. “We have almost 100 times less virological information than in the past, so with that there is a bit more uncertainty,” says Dr Webby.

Even so, Dr Webby and Dr Stewart urge everyone to get a flu shot: “As we’ve seen with the COVID vaccine, even if the flu shot doesn’t prevent you from getting infected, it definitely lowers your risk of getting seriously ill, ”says Dr. Webby. And Dr. Stewart adds that even though the flu shot is only 50% effective, “that 50% is really important because the flu can kill! she says. “This can lead to serious illness, especially in our vulnerable populations, such as those over 65 or with a history of asthma or COPD, or children under two.”

And again, as we’ve seen with the COVID vaccine, the flu vaccine can reduce a fatal illness requiring hospitalization to a mild case that can be treated at home. Although studies vary from year to year, the risk of landing in intensive care with the flu drops from 26% to 82% if you are vaccinated. A study earlier this year in Vaccine reported that there was a 31 percent reduced risk of death compared to those who were not vaccinated. And even if you’re one of the unlucky few to get the shot and still land in intensive care, your stay will be shorter. A 2018 study found that among people admitted to intensive care with influenza, vaccinated patients spent 4 days less than unvaccinated people.