Why do some people feel worse after their second COVID-19 vaccine dose? Your vaccine questions, answered – The Boston Globe


People who have been vaccinated might experience pain, redness, and swelling on the arm where you got the shot, according to the CDC. Others may feel worse, with headaches, tiredness, muscle pain, chills, fever, or nausea. Most symptoms resolve within one to three days.

Dr. Gabriela Andujar Vazquez, an infectious disease physician at Tufts Medical Center and the medical director for the hospital’s COVID-19 vaccine program, said some people have also reported enlarged lymph nodes after they’ve been vaccinated. The vaccine goes to the lymphatic system where cells produce immunity, and enlarged lymph nodes indicate that your body is working to produce antibodies. That side effect is more common in younger people, she said.

Madhavan emphasized that side affects from the vaccine are reflective of the body’s immune system response and not the virus itself, because the vaccines approved for use in the United States don’t contain live virus.

Why are younger people more likely to feel side effects than older people?

According to CDC data, people between 18 and 49 are more likely to feel side effects from the vaccine than those who are older.

The data was collected through V-safe, a CDC program that allows vaccine recipients to self-report any side effects they may be experiencing. Andujar Vazquez cautioned younger people may be more likely to report their symptoms than older people, which might skew the numbers. However, there is a biological explanation: young people tend to have a more robust immune system, she said.


“As opposed to an elderly patient with comorbidities and a weak immune system, side effects may not be prominent because the immune system is not young,” she said.

She noted that the symptoms do not differ between younger and older people, but they appear more frequently in the younger age group.

What if I don’t feel any side effects?

If all you feel after getting vaccinated is arm soreness, it doesn’t mean the vaccine isn’t working.

There are a range of factors that contribute to the way a person responds to a vaccine, Madhavan said, including their age, risk factors, medications one takes, and how active someone’s immune system might be on a given day. A person’s immune system doesn’t have to generate a response to be working.

“Individuals are different,” Andjuar Vazquez said. “Even though we’re made of the same materials, we all have different medical problems and immune systems. It doesn’t mean that if you don’t have chills and a fever that you don’t have immunity. Each of us respond differently.”

Andujar Vazquez said that data show that the “robustness of side effects doesn’t necessarily correlate with the amount of immunity,” because the clinical trials for the Pfizer and Moderna vaccines looked at six months post-vaccination and found that people still had immunity against the virus, and the pool of participants in the trials included people of all ages who reported experiencing a range of side effects.


Is it true that I might feel worse after the second shot than the first?

With the Pfizer and Moderna vaccines, which require two shots for full protection, side effects are more common after the second shot among some people, according to the CDC. That’s because the body is trying to respond more robustly to the vaccine after recognizing it from the first dose, Andujar Vazquez said.

“You have some circulating antibodies against the synthetic, dummy virus and then when you get the second dose, your body responds even more because you already had antibodies from that first dose,” she said. “And that’s what creates the full immune response.”

The first dose operates as a primer to the second dose, she noted.

“The first dose creates good protection, but that second dose closes the deal and makes it more robust, which is probably why we respond more,” Andujar Vazquez said.

How can I treat the side effects at home?

Madhavan said that those who just received their COVID-19 vaccine should try to rest, stay hydrated, and anticipate possibly being away from work for a day or two.

Andujar Vazquez said the side effects respond well to medicines like Tylenol, and the CDC’s website says you can take ibuprofen, acetaminophen, aspirin, or antihistamines for any pain or discomfort you feel after the shot if you take those medications normally. The agency also recommends people who have been vaccinated speak to their doctor about taking over-the-counter medication to treat side effects.


Enlarged lymph nodes can be treated by applying warm compresses to the area, Andujar Vazquez said, and the swelling typically goes away in a couple of days.

The CDC advises that people should contact their doctor if the redness or tenderness where they got the shot gets worse after 24 hours or if their side effects are worrying and don’t appear to be going away after a few days.

Experts say the benefits of the vaccine outweigh the risks of COVID-19. Here’s why.

Despite reports of expected side effects after being vaccinated, the Food and Drug Administration has deemed the vaccines safe and effective in preventing serious illness and death due to COVID-19. Public health officials are urging all adults 16 and older to get vaccinated, noting that the benefits of getting vaccinated far outweigh the risks of becoming infected with the virus.

Even if it’s a mild infection, someone who tests positive for COVID-19 will need to stay home or be isolated from their family, either to recover from the symptoms of the virus, or to avoid spreading the virus to others. The quarantine period that comes with getting infected lasts longer than side effects from the vaccine, Madhavan said.

“We know that there’s so many risks to an individual and that individual’s family and community with active COVID-19 infection, and that those far outweigh the risks of being out for a day or two — or not even that — after getting the vaccine,” Madhavan said.

Andujar Vazquez also noted that the side effects from the vaccine are expected, and people are aware of how they might feel ahead of time, whereas if someone is infected with the virus, there is a greater degree of uncertainty.


“You have no predictability with COVID-19,” she said. “You know if you have the vaccine you will get x, y, and z symptoms, and they will last for a day and they’ll be done.’’

Amanda Kaufman can be reached at amanda.kaufman@globe.com. Follow her on Twitter @amandakauf1.

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Why do some people feel worse after their second COVID-19 vaccine dose? Your vaccine questions, answered – The Boston Globe

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