Doctors Explain Why Getting COVID Vaccine Side Effects Mean It’s Working

Plus, why you shouldn’t worry if you *don’t* get any.

by JR Thorpe
Young woman lying back on a sofa in her living room at home. Doctors explain why getting covid vacci...
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You get your first COVID shot, head home — and are beset by a bunch of symptoms out of the flu playbook, from chills to fever, fatigue, and aches. All three vaccines currently given emergency use authorization in the U.S. by the FDA have various side effects, but experts tell Bustle that they’re not bad news at all: in fact, side effects from your COVID vaccine are a good sign. But if you don’t get any symptoms at all, you shouldn’t worry that you’re somehow missing out on some important vaccine protection.

Why The COVID-19 Vaccines Cause Side Effects

Side effects are to be expected from all the available COVID vaccines, Dr. Kathleen Jordan M.D., an infectious disease doctor and SVP of medical affairs at medical provider Tia, tells Bustle. “These symptoms are from an immune response to the vaccine — which is the desired effect,” she says. Whether you get a dose of an mRNA vaccine or one that uses a variant on a cold virus, the vaccines are designed to train your immune system into recognizing and fighting COVID. The shorts put your immune cells through their paces, so that they remember this dangerous new pathogen in the future. That can mean some temporary — but normal — unpleasantness.

“I like to refer to these fevers, fatigue, or body aches as ‘post-vaccine symptoms’ rather than even calling them side effects, as they are expected,” family physician Dr. Natasha Bhuyan M.D., a doctor with medical provider One Medical, tells Bustle. Science reported in November 2020 that if you’re having a two-dose vaccine and had a reaction to the first jab, you’ll likely experience more of the same with your second.

Does Everyone Get The Same COVID-19 Vaccine Side Effects?

These post-vaccine symptoms are more common in some people than others. “More side effects were reported in younger age groups, so some have hypothesized that these increased younger side effects indicate a more effective response of the immune system,” Dr. Jordan says. But that’s not actually the case. COVID vaccines, she says, are generally equally effective in all age groups; young people aren’t getting more protection than elderly people.

Some side effects have been more concerning to scientists than others. The American College of Allergy, Asthma and Immunology (ACAAI) reported in March 2021 that around five people per million given the Pfizer vaccine, and 2.5 per million given the Moderna shots, would likely experience a severe anaphylactic allergic reaction. That’s a very low rate, but if you experience anaphylaxis after one dose of a COVID vaccine, the Centers for Disease Control & Prevention (CDC) says you can’t get a second one.

What If I Don’t Have Any Side Effects After The COVID-19 Vaccine?

Side effects won’t happen to everybody, and if you sail through your vaccine doses with nary a headache or a chill, you’re not somehow less immune to COVID afterwards. “Most people in the Pfizer, Moderna, and Jannsen studies did not have [severe] side effects, yet the vaccines were highly efficacious in preventing severe disease across all groups,” Professor John A. Sellick D.O. M.S., an expert in infectious disease from the Jacobs School of Medicine and Biomedical Sciences at the University of Buffalo, tells Bustle. “No one should interpret the lack of side effects as meaning the vaccine did not ‘take’ or work.” Dr. Jordan points out that everybody who was jabbed in the clinical trials saw the benefits of the vaccines — aka, not getting sick from COVID — whether they had fatigue and fevers or not. “I would certainly not be worried if you experience no side effects,” she says.

How Long Do COVID-19 Vaccine Side Effects Last?

Being flattened by your vaccine dose is no picnic, but Dr. Jordan says your experience will most likely be short-lived. “Side effects resolve in 24 to 28 hours, and pale in comparison to symptoms of COVID-19, which can be quite severe, sometimes life-threatening, and not infrequently continue for months,” she says. It’s a good idea to prepare for the possibility of some unpleasant post-vaccine symptoms before you go to your shot appointments, though. Blankets and hot tea ahoy.


Dr Natasha Bhuyan M.D.

Dr. Kathleen Jordan M.D.

Professor John A. Sellick D.O. M.S.