COVID-19 Vaccine Side Effects (and how to prevent them)

I’ve been working at our medical center’s COVID-19 vaccine clinics for the past couple of months. We vaccinate about 3,500 people per day at our OSU Schottenstein Center site (the basketball arena) and about 275 people per day at our hospital-based vaccine clinic. Because of the potential for allergic reactions, we have either an emergency medicine physician or a critical care physician on site to manage any reactions. After supervising thousands of vaccinations, I’ve learned a lot about the vaccine reactions that people can get.

Younger people have more side effects

COVID-19 infection is much more severe the older we get. For people over age 80, the mortality rate of the infection is about 25% but for people under age 18, the mortality rate is negligible. It is just the opposite for side effects from the COVID-19 vaccines: older people are less likely to have side effect than younger people. I’m always relieved when I look over the list of the day’s vaccination schedule and see mostly people over age 60 because I know that I’m going to have an easy day.

Sore arms

Most people (about 75%) get a sore arm after the vaccination. It doesn’t typically occur for several hours after the injection and goes away within 2 days. I liken it to a bit more soreness than flu shot but less soreness than a tetanus shot. As with most other vaccines, the COVID-19 vaccines are given intramuscularly, into the deltoid muscle in the upper arm. One simple way of minimizing arm discomfort after the vaccination is to be sure that the arm is relaxed as much as possible when the needle goes in. If the deltoid muscle is tense when you get your vaccination, you are more likely to have pain later on. If there is swelling and redness at the injection site, a cold compress can help. If there is significant pain, it is OK to take acetaminophen (Tylenol) or whatever non-steroidal anti-inflammatory drug (eg, ibuprofen or naproxen) you normally take. Do not take any medications preventively and only take them if symptoms develop. Avoid taking corticosteroid medications (eg, prednisone) to treat arm pain or swelling since steroids can reduce the body’s immune response to the vaccine. If you anticipate needing to do a lot of writing or some other activity that involves your dominant hand, then get the vaccine in the non-dominant arm.

Aches, fever, and chills

It is difficult to predict who will get muscle aches, headaches, chills, or fever after the COVID-19 vaccine. The good news is that most people do not get these side effects. In general, younger people are more likely to get them than older people and people are more likely to get them after the second dose than the first dose. People who have had COVID infection in the past are also more likely to get more vaccine side effects, especially with the first dose of a vaccine. Although the timing can vary, it is typically about 18 hours after the vaccination. It is a good idea to have acetaminophen on hand and then take it at the early signs of fever or body aches in order to prevent experiencing more severe symptoms. For most people, these side effects resolve by 36-48 hours after the injection. The important thing to know is that these symptoms are NOT an indication of an infection and are instead an expected reaction of the body’s immune system to the vaccine.


Many people will be tired the day of and after their vaccine. For some, this can be severe enough to stay home from work. Because of this, we tried to stagger the vaccinations for our operating room nurses and the nurses on individual nursing units since we knew that a percentage of them were likely going to call off work the next day. Similarly, if you operate a restaurant or store, try to keep all of your employees from getting vaccinated on the same day or you might find yourself having to close shop the next day. To minimize fatigue, keep hydrated and plan on an extra 1-2 hours of sleep the night after your vaccine. An afternoon nap may be in order, also.


This is the most serious side effect of the COVID-19 vaccines and it is fortunately vary rare. This is a severe allergic reaction that can cause difficulty breathing and shock. It occurs shortly after the vaccination, within the first 30 minutes. It responds very well to epinephrine injection and we keep epinephrine on hand, just in case of anaphylaxis. In my own experience, many of the people who were initially thought to have anaphylaxis didn’t actually have it – vocal cord dysfunction and vagal reaction are common masqueraders of anaphylaxis (and far less serious). The main component of the Pfizer and Moderna vaccines that can cause severe allergy is polyethylene glycol. This is the same ingredient in the laxative, MiraLAX, and the prep used for colonoscopy, Go=lytely. If a person has not had an allergy to these ingredients in the past, then they usually do not have any problem with the COVID-19 vaccine.


Less life-threatening allergic reactions can show up with a rash or itching, rather than anaphylaxis. These reactions are also quite uncommon but can be fairly easily treated with antihistamines (eg, Benadryl). Isolated rash does not warrant a trip to the emergency department but these patients should be watched a little longer than other patients to be completely sure that they do not progress to anaphylaxis.

Avoidable side effects

By far, the most common symptoms we see at the time of vaccination are avoidable:

  • Vagal reactions. This is what happens when a person faints and a lot of people faint at the sight of needles, regardless of what is inside of that needle. If a person is going to develop a vagal reaction, then they will develop it even if there was nothing in the syringe. The symptoms are feeling light-headed, clammy, nauseas, and sweaty. One of the best ways to prevent a person from having a vagal reaction to a COVID-19 vaccination is to distract them by talking to them while the nurse is giving the vaccine in order to take their mind off of the vaccine. When someone does develop a vagal reaction, have them lay down, preferably with their feet elevated. If a person tells you that they faint or get dizzy every time they get a vaccine, then put them in a reclining chair before you give them the COVID-19 vaccination. Ensuring that the person is adequately hydrated is important. The most common treatments that I give out in the vaccine clinics are bottle of water.
  • Hyperventilation. Many people are afraid of vaccinations and doubly afraid of the COVID-19 vaccine. Maybe they read something written by an anti-vaxxer or maybe they heard a horror story from their neighbor about how awful the neighbor felt after their vaccination. These patients are prone to panic attacks. The symptoms are dizziness, shortness of breath, and tingling in the fingers and hands. From a physiologic standpoint, these symptoms are caused by an acute respiratory alkalosis causing the pH of the blood to rapidly rise – this is due to breathing too rapidly and too deeply. Patients who get hyperventilation after their COVID-19 vaccination need to be talked down from it – focus on slower and shallower respirations. This can be hard to do since the rapid, deep breathing is being caused by anxiety. Reassurance and having the person breath through their nose (rather than mouth) is usually all it takes. Once patients realize that the symptoms are from hyperventilation, they usually calm down. In the past, this would have been treated by breathing into a paper bag to re-circulate carbon dioxide and prevent the blood carbon dioxide from dropping too low.
  • Hypoglycemia and dehydration. This is by far and away the most common problem that I encounter at our vaccine clinic. It is also a risk factor for vagal reactions. Many people get up in the morning and go straight to the clinic to get their COVID-19 vaccine before they have breakfast. Couple an empty stomach with the fear and excitement of a vaccine and you get a bunch of queazy, dizzy vaccine recipients. Encourage people to have breakfast before their vaccine and keep up with their fluids. This can be an especially big problem when we are vaccinating college students on the weekends who stayed up late the night before drinking beer. Being dehydrated and having an empty stomach is a set-up for getting a vagal reaction
  • Grouchiness. This is another very common symptom we see in the vaccine clinic and is usually caused by¬†hypocaffeination. Just like skipping breakfast before your vaccine is a bad idea, skipping your morning coffee can result in having a headache, feeling tired out, and having a generally bad attitude. If you are a coffee or tea drinker, have a cup before you go to the vaccine clinic.
  • Vocal cord dysfunction. In the pulmonary clinic, vocal cord dysfunction (VCD) is a common mimic of asthma. It occurs when the muscles that control the vocal cords are under excessive tension resulting in the space between the vocal cords being constricted and too narrow. This causes shortness of breath, particularly when trying to breath in (as opposed to breathing out). Some patients will say that they they feel like air is getting stuck at the top of their neck. Anxiety can precipitate vocal cord dysfunction. One of the problems with VCD is that it can not only mimic asthma but can also mimic anaphylaxis and the treatment for anaphylaxis (epinephrine) can often make the VCD worse. In our vaccine clinic, I saw a person who was their for their second dose of the COVID-19 vaccine. With the first dose, she had developed what was thought at the time to be anaphylaxis and was given epinephrine that did not help and in fact seemed to make her breathing worse. The EMS squad was called and took her to the emergency department where a particularly bright physician obtained a blood tryptase level. Anaphylaxis causes the tryptase level to be elevated and hers was normal. For her second dose, we had a nurse sit with her and provided lots of reassurance and distracting conversation. We told her to breath through her nose (which can help reduce the tension on the vocal cords). In the end, she had no problems at all after her second dose. With all that being said, VCD is never a life-threatening problem but anaphylaxis is – when in doubt about whether it is VCD or anaphylaxis, treat the persons as if it is anaphylaxis.
  • Boredom. You can always pick out the people who are in the vaccine clinic for their second dose (as opposed to their first dose). They bring a book, newspaper, or crossword puzzle. Sitting in the clinic for 15 minutes with nothing to do except look at the other people getting vaccinated can be pretty boring and that boredom can be double the amount if you have to wait 30 minutes because of a past history of severe allergies.

The COVID-19 vaccines are safe. Period. Yes, they can sometimes have annoying side effects but no one dies from the COVID vaccine whereas more than a half of a million Americans have died of COVD-19. By getting a COVID-19 vaccination, you are saving a life – if not yours, then one of your family members or someone in your community. A sore arm or fatigue for a day is a small price to pay.

April 3, 2021

By James Allen, MD

I am a Professor Emeritus of Internal Medicine at the Ohio State University and former Medical Director of Ohio State University East Hospital