- Only one-quarter of people who received a COVID-19 vaccine had side effects such as headache or fatigue, with local reactions to the vaccine much more common.
- In a new study, researchers from the United Kingdom used data to look at side effects experienced by over 627,000 people.
- Among people who were vaccinated, 25.4 percent reported having a systemic side effect — one that occurs in a part of the body other than near where the vaccine is injected.
Across social media, people who’ve received the COVID-19 vaccine are sharing stories of the temporary side effects they’ve willingly endured to gain immunity from a virus that has killed millions of people worldwide.
For many, this is a badge of honor, much like the FOMO-inducing vaccine selfie.
One person on Twitter compared the side effects to “the worst hangover” they’ve ever had, with another saying the second dose of the mRNA vaccine hit them “like a truck.”
While systemic side effects such as fatigue and headache can occur after receiving the COVID-19 vaccine, a new study suggests that only around 1 in 4 people actually experience them.
Much more common — and also short-lived — are local reactions, such as pain or redness at the site of injection.
“This study shows that most people don't experience side effects such as headache and fatigue, and although these have been reported on social media, it is reassuring that many of us will not get those side effects,” said Dr. Veronica Contreras, a family medicine specialist with AltaMed.
Local and systemic side effects
In the study, researchers from the United Kingdom used data from a COVID-19 symptom app to look at side effects experienced by over 627,000 people who received either the Pfizer-BioNTech or AstraZeneca-Oxford COVID-19 vaccines.
Among people who were vaccinated, 25.4 percent — or 1 in 4 people — reported having a systemic side effect, one that occurs in a part of the body other than near where the vaccine is injected.
The most common systemic side effects were fatigue and headache. They generally appeared within the first 24 hours after vaccination and lasted on average about 1 day.
Local side effects were much more common — occurring in 66.2 percent of people — with tenderness and pain near the injection site most frequently reported.
These generally began the day after injection and lasted about 1 day.
Other side effects such as rashes, a burning sensation on the skin, or red welts on the lips and face, were reported by a small number of people — less than 2 percent.
The results were published April 28 in the journal The Lancet Infectious Diseases.
Dr. Jose Mayorga, executive director of the UCI Health Family Health Centers and assistant clinical professor of family medicine with UCI School of Medicine, hopes the results of this study will help people who are hesitant about getting vaccinated.
“Mild side effects should be expected if we receive a COVID-19 vaccine, just like other vaccines we receive,” he added. “These mild side effects are short-lived, for a COVID-19 vaccine that provides great gains — protection from an unpredictable virus that has caused so much devastation and loss.”
First dose versus second dose
For the Pfizer-BioNTech vaccine, systemic side effects were worse after the second dose — 22 percent of people reported side effects after the second dose, compared to 11.7 percent after the first.
Systemic side effects were more common after the first dose of the AstraZeneca-Oxford vaccine — 33.7 percent. Researchers didn't look at data on side effects after the second dose of this vaccine.
For people who received two doses of the Pfizer-BioNTech vaccine, local side effects were slightly less frequent after the second dose (68.5 percent) than the first dose (71.9 percent).
Local side effects were also less common after the first dose of the AstraZeneca vaccine (58.7 percent).
Age, sex, and previous infection
People under age 55 were more likely to report either systemic or local side effects after either vaccine, compared to older adults.
Women were also more likely than men to report side effects after the first dose of either vaccine.
In addition, people who had a previous case of COVID-19 were about 3 times more likely to have systemic side effects after either dose of the Pfizer-BioNTech vaccine, compared to people with no prior infection.
They were also about twice as likely to have systemic side effects after the first dose of the AstraZeneca vaccine. Local side effects were also higher for both vaccines in people who had COVID-19.
Concerns about side effects
It's not unusual for someone to have concerns about vaccine side effects, especially when they see others posting on social media about negative experiences.
Mayorga said when he talks to someone who's hesitant to get the COVID-19 vaccine, he likes to frame vaccination in a larger context.
“The risk from a serious [case] that can cause numerous problems, including hospitalization and death, is not a chance they want to take,” he said. “We need to move away from the side effect conversation and return to [talking about] the impact this pandemic has had on all of us, and how the vaccine can end this pandemic.”
Contreras suggests that people who have concerns about COVID-19 vaccines talk to friends or family members who have been vaccinated, or reach out to their physician.
“People have to decide for themselves if they are willing to take the risk of getting COVID, or if they would like to be protected by a vaccine that is highly effective,” she said.
“As physicians, we are here to answer any questions or concerns patients may have, so they can make the best informed decision for themselves,” she added.