A recent study has found that more people report side effects after receiving a dose of the Moderna COVID-19 vaccine than the Pfizer vaccine.
Published Monday in the journal JAMA Insights, the study shines light on the many mild side effects of both vaccines — including headache, fever, chills and pain or swelling at the injection site.
Between Dec. 14 and Feb. 28, about 1,085,000 people reported symptoms from the Pfizer vaccine after the first dose. Around 1,465,000 reported symptoms from the first shot of the Moderna vaccine in the same period.
For the second dose, approximately 666,000 people reported side effects from the Pfizer vaccine, compared to 777,000 with the Moderna vaccine.
The researchers compiled the data from the Centers for Disease Control’s V-safe surveillance system, which reports side effects to a variety of vaccines, including the new COVID-19 vaccines.
For both doses of the vaccine, the reaction was highest on day one after vaccination and steadily declined through day seven, the study found.
The study also reports that people younger than 65 years of age reported more side effects to V-safe, compared to those 65 years and older — a common finding for vaccines.
Women and younger people tend to experience more side effects from vaccines generally.
“That’s not to say they have more symptoms, however,” Stanford University infectious disease physician Anne Liu said, adding that it’s possible that younger folks and women just report their symptoms with more frequency.
“I’m going to make a big generalization here, but our culture typically discourages men from bringing their symptoms to attention,” Liu said.
As for why younger people experience more symptoms, that could be a result of them having stronger immune systems.
“Older people’s immune systems tend to get weaker over time,” Liu explained, meaning their reaction to the vaccine will be less intense.
“If you have no side effects, you may have a weaker response,” Liu said.
That doesn’t mean the vaccine isn’t working. The immune system is complex and multi-pronged, and side effects aren’t the only sign the vaccine is efficacious.