Flu cases are soaring, and they’re not likely to let up anytime soon. In fact, the Centers for Disease Control and Prevention estimates that since Oct. 1, 2024, at least 24 million people have been sickened by influenza. Of those cases, at least 310,000 people have been hospitalized — the highest number since 2017 — and at least 13,000 people have died. 

As Michigan and many other states continue to report very high influenza rates, it’s critical to stay informed about how to protect yourself against the flu. Victor DiRita, Rudolph Hugh Endowed Professor and chair of the Michigan State University College of Natural Science’s Department of Microbiology, Genetics and Immunology, says the best weapon we have against this illness is the flu vaccine. And with cases still rampant, it’s not too late to get vaccinated if you put it off this year.

The College of Natural Science recently sat down with DiRita to talk about the flu vaccine, how it’s made and what protection it provides to those who get it.

How is the influenza vaccine created each year?

An advisory committee looks at strains of influenza circulating in populations. There are ways we’ve historically been able to do that because these viruses tend to circulate in other species. We can determine what’s coming out of those species and predict what might be coming into the human population. Then pharmaceutical companies produce different types of vaccines. We have some targeting both influenza A and influenza B, or just influenza A — or components of different types, so they’re different valencies, meaning the number of targets.

Every year it’s a little bit of a guess. We think we’re going to have this lineage that we need to target, but are we right or are we wrong? That often dictates whether we have a good take of the vaccine.

There are two major molecules that we’re targeting in the virus: one is H and one is N. Those Hs and Ns can have different types even among them. For example, we’re hearing about bird flu now, which is H5N1. These are just different types of those two proteins, and those are what we tend to target with the vaccines.

How do vaccines work?

Vaccines are intended to stimulate your immune system to respond as if it was responding to the actual infection. Your body produces the weapons your immune system would use in a natural infection, called antibodies, but it would have those weapons present beforehand. It’s intended to do so without causing you to become sick, which happens when viruses cause your immune system to mount an attack against them.

We’re trying to stimulate and prepare your immune system to see the actual infection and respond more rapidly than it would have had it not been stimulated by the vaccine.

Why do we need the flu vaccine every year when other vaccines are given only once or twice?

In large part, that’s because of the changing nature of the virus each year. There are reservoirs for this virus outside of humans, and you get a variation of the virus’s genetic components within those other reservoirs. When they come out of those reservoirs back into humans, we may or may not have protection against them.

We don’t typically see the same high degree of variation with other viruses that we vaccinate against, with the exception of COVID-19. That’s why they’re constantly upgrading and changing the vaccines. But it just depends on how much variation occurs within the population of the virus. 

One thing I hear frequently is, “I got the vaccine, but I still got sick.” Does that mean the vaccine didn’t work?

You can get the vaccine and still get sick. But what I teach medical students is that their patients need to understand that you don’t take the flu vaccine so that you don’t get sick from the flu. You take it so you don’t die from the flu. That’s why we get vaccinated — because flu can kill you. You may still mount a pretty aggressive response to flu. But with the vaccine on board, you are more likely to survive the infection.

I’ve had flu in years where I’ve been vaccinated and it’s miserable. But without the vaccine, the possibility of dying is much higher. It’s always the goal to keep you alive. 

Are there years when the people creating the vaccine guess incorrectly about the strains that circulate that year?

Yes. You can start to see this as the flu season is older by looking at the morbidity rate of people who are getting sick. With the higher rate of infection this year, it seems maybe we didn’t do as well, although we do have, unfortunately, a growing and misguided skepticism about vaccines. 

Do you recommend people get the vaccine every year?

I get it every year. I absolutely recommend it. Flu is a lethal disease, and people just need to understand that you don’t have to be in a particular demographic for flu to kill you. It’s an equal opportunity killer. The vaccine is the reason we’re able to live with it and not worry too much about flu season. If we didn’t have the vaccine, we’d have a totally different attitude.