You can get Covid-19 and flu vaccines at the same time, but should you? What the science says

With holiday season underway, you may be realizing that you forgot to get your Covid-19 and flu vaccines, and now you’ll be sitting across the table from your elderly relatives.

The good news is that it’s not too late to get your shots, but what about knocking them both out at the same time? The US Centers for Disease Control and Prevention says this is an option, but should you?

A recent study of Medicare claims data found a slightly increased — but still very rare— risk of stroke for seniors who get a high-dose influenza vaccine and Covid-19 shot at the same time. The risk was about 3 strokes for every 100,000 doses of Pfizer’s bivalent Covid vaccine and about 3 transient ischemic attacks for every 100,000 doses of Moderna’s bivalent Covid vaccine. Other studies have not found the same risk, leading the CDC and US Food and Drug Administration to say there’s no change to their vaccine recommendations at this time. Covid-19 vaccines were updated this year to target one strain of the coronavirus rather than two.

Beyond that, getting both shots at the same time does seem to make it a bit more likely that you’ll experience a temporary reaction to the shots; the most common symptoms reported in a government study were fatigue, headache and muscle pain.

CDC Director Dr. Mandy Cohen told CNN that the most important thing is for people to get their vaccines at all — and that early in respiratory virus season is a good time to do it.

“It definitely is OK for you to get multiple vaccines on the same day,” Cohen said. “I would talk to your doctor or nurse practitioner about what’s right for you.”

Does co-administration affect protection?

But what about effectiveness? Does getting both shots together affect how well they work?

Here’s where there might be an upside.

A small study presented at the recent Vaccines 2023 conference in Boston found that health care workers who got flu and bivalent Covid-19 shots on the same day had higher antibody responses right after they got them, as well as six months later, compared with people who got their shots on different days.

Susanna Barouch, a high school student in Cambridge, Massachusetts, who led the research, said she thinks that giving the shots at the same time may prod the immune system to react more strongly to shots. “The flu vaccine might have been an adjuvant for the Covid vaccine,” she said.

But this hasn’t been the only study to look at the question, and perplexingly, other studies have come to the opposite conclusion or found essentially no difference between giving the vaccines together or one at a time.

This is one of the first studies to find that co-administration increases antibody levels, and Barouch says its findings need to be replicated before they’re accepted as fact.

“Definitely, I would say this is far from settled,” said Stephen Moss, a researcher at the University of Michigan.

Moss led a recent study that compared neutralizing antibody responses of 53 Israeli health care workers who received their bivalent Covid-19 vaccines separately or with a flu shot.

Blood samples from these health care workers were equally able to prevent Covid-19 and flu viruses from infecting cells, whether they got their vaccines together or separately.

A study from the Netherlands, published in June, found that antibodies after co-administration showed significantly lower neutralization capacity compared with a reference group that got their vaccines separately.

Moss said most studies of co-administration have found either “a slight increase, a slight decrease or no change whatsoever,” in antibody levels, he said.

What that means, he says, is that from a broader public health perspective, it’s probably a good idea to recommend that people get both at the same time.

“It cuts down on doctor’s visits. It cuts down on the number of encounters with the health care system you have to have. It also cuts down on the number of days you feel like crap after the vaccine. So you only have to go through that once rather than twice,” Moss said.

Real world outcomes

Reassuringly, a large recent study by researchers at Pfizer, which looked at the health outcomes in people who got their flu and Covid-19 vaccines together or separately, found little difference between these groups.

The study found that rates of hospitalizations, emergency room visits and doctor’s visits were similar between both groups. Overall, the group that got both shots at the same time was slightly more likely to visit the doctor or emergency room for Covid-19 but less likely to need medical care for the flu, suggesting that getting both shots together improved immune protection against influenza infections.

So how you get your vaccines comes down largely to personal preference, but Dr. William Schaffner, an infectious disease expert at Vanderbilt University, says that getting them together makes a lot of sense, especially this far into the season.

“I would just remind everyone that a vaccine deferred is often a vaccine never received, because you have to make another effort to go in,” he said.