Tis the season to get vaccinated! We in the Northern Hemisphere are rapidly approaching the shortest day of the year, and that means it’s time to think about protecting yourself against the flu and COVID-19. It would be convenient to get both shots at the same time, but is it safe? Yes, is the resounding conclusion from a new study.
Both flu and COVID-19 vaccines are currently recommended in the US – where the study was conducted – for adults and kids over the age of 6 months.
The optimal time to get your seasonal flu shot, according to the Food and Drug Administration (FDA), is right now: flu activity peaks between December and February, so it’s definitely not too late to get protected.
COVID-19, as we know, doesn’t follow the same seasonal pattern as the flu – but during the years of the pandemic, we’ve reliably seen peaks in infections in the wintertime. If you haven’t yet had an updated 2024-25 COVID-19 shot, the Centers for Disease Control and Prevention (CDC) says you can get one – for most people, you just have to wait two months since your last booster.
To get as much coverage of these two vaccines as possible, clinicians in the US are permitted to administer both of them simultaneously, but the authors of the new study point out that when they planned their research, there was limited hard scientific data around this approach.
As such, the authors conducted a clinical trial during two flu seasons – 2021-22 and 2022-23 – at three sites: Cincinnati Children’s Hospital Medical Center, Duke University, and The Johns Hopkins University.
In the end, they obtained data from 334 people who received both an mRNA COVID-19 vaccine and an inactivated flu vaccine formulated for that particular season. The subjects were randomized to receive the two shots either sequentially or simultaneously.
The primary outcome the researchers were looking at was reactogenicity – did the participants experience common indications of an immune reaction like fever and muscle pains, and did this happen more often in those getting both shots together? They also looked at other adverse events occurring in the seven days immediately following each vaccine, as well as serious adverse events within the following 121 days.
“Approximately 10.7 percent to 26.8 percent of participants in the trial reported moderate or severe injection site pain, fatigue, myalgia, headache, or chills after receipt of mRNA COVID-19 vaccine,” the authors write, which they note is what you would expect to see based on testing of these vaccines prior to licensing. The incidence of side effects from the flu vaccines was also within expectations.
After analyzing the data, the team found that reactogenicity was comparable across both the sequential and simultaneous groups. There was no evidence of any safety concerns with giving both vaccines at the same time, and the participants didn’t react any worse, on average, than those whose shots were spaced out.
One key limitation they note is that the study was underpowered – due to logistical issues, they weren’t able to recruit as many participants as they would have liked. They also note that they plan a future study focusing on pregnant people, who were excluded from this research.
Overall, though: “This trial lends support to the option of simultaneous administration of these vaccines,” the authors conclude, “which is a strategy to achieve high levels of vaccination coverage during anticipated periods of increased influenza and SARS-CoV-2 virus transmission.”
The study is published in the journal JAMA Network Open.
