It’s vaccination season, which for most people means getting immunized for flu and COVID-19 (and RSV for infants, pregnant women, or people 75 and older).
Public-health officials have said before that getting the two shots at the same time is safe, but some people have remained worried about receiving both vaccines together. Now, a new study confirms that safety. In what the researchers say is the first randomized, placebo-controlled trial analyzing the side effects of the co-administration of the vaccines in the U.S., they found no difference among people who received the COVID-19 and flu shots simultaneously in different arms and those who got the shots spaced apart by a week or two.
Dr. Emmanuel Walter, chief medical office of the Duke Human Vaccine Institute and professor of pediatrics at Duke University School of Medicine, and his team studied 335 people who were randomly assigned over two visits to receive a COVID-19 mRNA vaccine and either a placebo flu shot or an actual flu shot. The visits were spaced one to two weeks apart.
Side effects, most of which were mild, aren’t unusual for these shots. Some people reported things like pain at the injection site, fever, muscle and joint aches, headache, chills, fatigue, nausea, and swelling under the arms during the seven days following the shots.
But Walter and his team found no difference between the two groups in the rates of these side effects, and no difference in quality-of-life surveys given to both groups.
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“The bottom line is that when we gave the vaccines together, we didn’t see an increase in the composite outcome of side effects when we spread them out over two visits,” says Walter.
Some experts have speculated that activating the immune system against two viruses simultaneously might lead to slightly more reactions, but that wasn’t the case in the study. The results support current recommendations from the U.S. Centers for Disease Control and Prevention that receiving the COVID-19 and flu shots at the same time is safe.
The rates of side effects were also similar regardless of whether people had had COVID-19 before or not—further supporting the safety of getting simultaneously vaccinated.
The current study did not explore whether the co-vaccination affects the effectiveness of either vaccine. There was some hint in the data that people who got the shots together might have more COVID-19 illness, but the association wasn’t statistically significant. Walter says he collected antibody information from the volunteers and plans to analyze the data more fully to answer that question in a future study.
Because of the small size of the study, he also was not able to fully determine if rare, more severe adverse events associated with either vaccine were also similar among those who received the two shots at the same time vs. separately.
“When this study was designed, we didn’t have any information on the safety of giving both [of these] vaccines together,” he says, although the long-standing safe practice of giving young children multiple vaccines at the same time suggested there was no reason for concern. “The results support that it’s okay for people to get both vaccines in the convenience of one visit rather than splitting them up into two visits.”
