CLEVELAND, Ohio — Experts say some of the most common side effects from the COVID-19 vaccine, such as fever and headache, can be signs the immune system is working as it’s intended.
Does that mean you’re “less immune” to the coronavirus if you don’t have any side effects?
Our readers have questions about the coronavirus vaccine, and cleveland.com is getting answers from health care experts.
Q. If you don’t have any side effects from the vaccine, are you “less immune” than someone who has strong side effects?
The short answer is no. The severity or number of side effects are not indicative of someone’s level of protection against COVID-19.
More than half of the participants in the clinical trials for the Pfizer/BioNTech and Moderna vaccines did not experience side effects, but both of those vaccines are roughly 95% effective at preventing symptomatic COVID-19 cases, said Dr. Amy Ray, the director of infection prevention at MetroHealth.
They are more common in younger patients, and tend to be less frequent in older adults, Ray said.
“You should not use the presence or absence of side effects as ‘proof’ of immunity,” Ray said in an email.
The immune system has two distinct responses after you get the vaccine, and side effects are only associated with the first, said Dr. James Fernandez, and allergy and immunology expert at the Cleveland Clinic.
That initial response, known as innate immunity, is the body’s first line of defense against a virus, bacteria or other pathogens. It kicks in shortly after you get vaccinated and can manifest in symptoms like arm pain or flu-like symptoms, Fernandez said.
Some people may have a very robust response, but most do not, he said.
“If you don’t have side effects, it doesn’t mean your immune system isn’t working,” Fernandez said. “It might just mean that it’s working appropriately and isn’t kind of overshooting.”
The second response is adaptive immunity, and that’s more important, Fernandez said. Adaptive immunity is the body learning to protect itself against pathogens like the virus that causes COVID-19. The body learns to recognize the virus and produces antibodies that protect it against infection.
Adaptive immunity develops over the course of the several weeks after you get each dose of vaccine. That’s why experts say full protection comes two weeks after your final dose.
“It’s really what the immune system does weeks later that is important,” Fernandez said. “I wouldn’t focus on those early side effects related to the vaccine to judge whether you had an [effective] response or not.”
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