This Is the Only Way to Tell If Your COVID Vaccine Worked, Doctors Say

Doctors warn that your side effects aren't the be-all-end-all of whether or not you're protected.

More than 51.5 million people are fully vaccinated against COVID across the U.S. as of Mar. 28, according to the latest Centers for Disease Control and Prevention (CDC) data—and that number continues to increase at a quick rate. So, you've either heard a lot about the wide range of reactions to the vaccines ahead of your dose, or you've felt them yourself. From the strange (like a metallic taste in your mouth) to the delayed (like a rash at the injection site) to the commonplace (like headache and fever), doctors are reassuring Americans that these side effects are indicators that your body is building immunity to the virus. However, if you don't have side effects, you might be wondering whether or not the vaccine is doing its job. In short, how do you know your vaccine was effective in protecting you against COVID-19? Read on to find out, and for more on possible reactions, check out If 1 of These 3 Body Parts Starts Swelling Up After Your Vaccine, Call a Doctor.

The best way to know your vaccine is working is if you get your recommended number of shots at the recommended intervals.

Shot of a doctor applying a band aid after injecting a patient in his arm with COVID vaccine
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As you likely know by know, there are two different kinds of vaccines—the mRNA vaccines from Pfizer and Moderna, which are given in two doses three weeks and four weeks apart respectively; and the adenovirus vaccine from Johnson & Johnson that's only one shot. Two weeks after the second Pfizer or Moderna dose and two weeks after the Johnson & Johnson dose you can consider yourself fully vaccinated. "Two doses of the Pfizer-BioNTech and Moderna COVID-19 vaccines are required for optimal vaccine effectiveness," the CDC explains.

So, the best way to know your vaccine is working is sticking "as close to the recommended interval as possible," the CDC states, though they note that in extenuating circumstances, "the second dose of Pfizer-BioNTech and Moderna COVID-19 vaccines may be administered up to 6 weeks (42 days) after the first dose."

The reason why they don't recommend stretching beyond that timeline is because there's no data on shorter or longer intervals between shots. "There is currently limited information on the effectiveness of receiving your second shot earlier than recommended or later than 6 weeks after the first shot," the CDC explains.

You can't rely on antibody tests to tell you if your vaccine worked.

coronavirus antibody test being given to white hand
Shutterstock/Cryptographer

While some people say your antibody levels are one of the most direct indicators of a vaccine's efficacy, the CDC advises otherwise. "Antibody testing is not recommended to assess for immunity to SARS-CoV-2 following COVID-19 vaccination," the agency notes on their website.

"After the vaccines, a lot people are going to get antibody testing—'Oh, I want to see if it's working.' It actually has very little correlation," infectious disease expert Rob Murphy, MD, told The Washington Post. "Many people will test negative on the antibody test, and that does not mean the vaccine didn't work."

And for more on preparing for your vaccine, check out The Only Medication You Should Take Before Your COVID Vaccine, Experts Say.

The "presence or absence of side effects" should not be used as immunity validation either.

Woman at Home Suffering From Headache
PixelsEffect / iStock

Amy Ray, MD, a director at MetroHealth, warned in an email to Cleveland.com that people should not "use the presence or absence of side effects as 'proof' of immunity." "If you don't have side effects, it doesn't mean your immune system isn't working," James Fernandez, MD, an allergy and immunology expert, who also spoke with the news outlet, said. "It might just mean that it's working appropriately and isn't kind of overshooting."

Fernandez noted how the immune system has two responses to vaccines—innate immunity and adaptive immunity, the first of which is immediate while the second is slower but most important. This is how the body learns to make antibodies used to fight against COVID, a process which could take a few weeks after the completed vaccine 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."

And for a new side effect to be aware of, check out The Strange New COVID Vaccine Side Effect That's Confusing Even Doctors.

There's no need to worry if you don't experience side effects.

Man getting the COVID vaccine
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In a recent blog post on GoodRX, Kelly Elterman, MD, a board-certified anesthesiologist in San Antonio, Texas, explained that a lack of side effects doesn't correlate with decreased immunity. "Only about 50 percent of people vaccinated with either the Pfizer or Moderna vaccines experienced side effects other than arm pain, while 95 percent were protected from COVID-19 infection," Elterman wrote. And less than half of Johnson & Johnson vaccine recipients developed side effects other than pain in the arm, "while up to 74 percent were protected from COVID-19 infection."

Though Elterman said there's no simple way to confirm if your vaccination worked, "the vaccine has been shown to be effective even in people who had no side effects at all," she said. "The good news is that because the vaccines are highly effective, it's very likely that they work even if you don't have any reaction to them."

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And the severity of your side effects doesn't predict how much immunity you have.

A women is feeling sick and sleeping on a sofa at home.
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Many patients who receive the COVID jab can plan to experience some of the most common side effects, ranging from pain, redness, or swelling in the injection site, or tiredness, headache, muscle pain throughout the body, chills, fever, or nausea, according to the CDC. Anna Wald, MD, an infectious diseases physician, recently told HuffPost that the vaccine's effectiveness is "unlikely to be determined by how severe your side effects are," the news outlet reported. And for a more on why certain people are hit harder by the vaccine's side effects, check out This Is Why Half of People Have Stronger Vaccine Side Effects, CDC Says.

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