Should You Get Covid-19 and Flu Vaccines Simultaneously? What the Research Reveals

As the holiday season is in full swing, you may be realizing that you missed getting your Covid-19 and flu vaccines, and soon you'll be in close contact with your elderly relatives.

The good news is that it's still possible to get vaccinated, but have you considered getting both vaccines at the same time? The US Centers for Disease Control and Prevention suggests this is an option, but is it a good idea?

A recent analysis of Medicare claims discovered a small but extremely rare increase in the risk of stroke for older adults who receive a high-dose influenza vaccine and a Covid-19 shot simultaneously. The increased risk equated to about 3 strokes for every 100,000 doses of Pfizer's two-component Covid vaccine and about 3 transient ischemic attacks for every 100,000 doses of Moderna's Covid vaccine. Nevertheless, other studies have not produced similar findings, leading the CDC and US Food and Drug Administration to maintain their current vaccine recommendations. It is worth noting that Covid-19 vaccines have been modified this year to target a single strain of the coronavirus rather than two.

Furthermore, receiving both vaccines concurrently does appear to slightly increase the likelihood of experiencing a temporary reaction to the shots; the most commonly reported symptoms in a government study were fatigue, headache, and muscle pain.

Dr. Mandy Cohen, the CDC Director, emphasized the importance of getting vaccinated, especially early in the respiratory virus season. She also mentioned that it is safe to receive multiple vaccines on the same day but advised consulting with a healthcare professional to determine the best course of action.

Does co-administration affect protection?

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

Potential benefits emerge here.

A recent study from the Vaccines 2023 conference in Boston revealed that healthcare workers who received flu and bivalent Covid-19 vaccinations on the same day exhibited stronger antibody responses immediately and six months later, compared to those who received their vaccinations on different days.

Susanna Barouch, a high school student from Cambridge, Massachusetts, believes that administering the shots concurrently could potentially stimulate a stronger immune response. "The flu vaccine may have acted as an adjuvant for the Covid vaccine," she suggested.

However, this is not the only study to explore this question, and confusingly, other studies have reached conflicting conclusions or observed virtually no difference between administering the vaccines simultaneously or separately.

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 theyre accepted as fact.

An ACVS pharmacist at the Baldwin Park store in Orlando, Florida, prepares to administer a shot of the new Pfizer/BioNTech vaccination booster, Comirnaty, for COVID-19 on September 15, 2023. Pharmacies nationwide have begun providing the new COVID-19 boosters, which are recommended for individuals aged 6 months and older by the Centers for Disease Control and Prevention. (Photo by Joe Burbank/Orlando Sentinel via AP)

According to Stephen Moss, a researcher at the University of Michigan, it is far from settled whether Covid shots may slightly increase the risk of stroke in older adults, especially when given with certain flu vaccines.

A recent study led by Moss compared the neutralizing antibody responses of 53 Israeli health care workers who received either separate or combined bivalent Covid-19 and flu vaccines. The blood samples from these workers were found to equally prevent both Covid-19 and flu viruses from infecting cells, regardless of whether they received the vaccines together or separately.

A study conducted in the Netherlands and published in June discovered that when vaccines are co-administrated, the antibodies produced have a significantly lower neutralization capacity compared to a reference group that received their vaccines separately. Moss explained that the majority of studies on co-administration have revealed only slight increases, slight decreases, or no change in antibody levels.

He explains that from a wider public health standpoint, it's likely best to advise people to get both vaccines simultaneously. This reduces the need for multiple doctor visits and encounters with the healthcare system. It also minimizes the number of days feeling unwell after getting the vaccine, allowing individuals to go through it once instead of twice.

Real world outcomes

A substantial new study conducted by Pfizer researchers examined the health outcomes of individuals who received their flu and Covid-19 vaccines either simultaneously or independently. The findings revealed minimal variance between these two groups, providing reassuring results.

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The research discovered that hospitalization, emergency room visits, and doctor's appointments rates were comparable in both groups. In general, the group that received both vaccinations simultaneously had a slightly higher likelihood of seeking medical attention for Covid-19 but were less likely to require medical care for the flu, indicating that receiving both shots together enhanced immune protection against influenza infections.

Ultimately, the choice of how to receive your vaccines largely depends on personal preference, but Dr. William Schaffner, an infectious disease expert at Vanderbilt University, suggests that getting them together makes sense, particularly at this stage in the season.