COVID-19 vaccines – What We Know About Side Effects and Safety.

Betty Chaffee/ January 14, 2021/ Coronavirus, COVID-19, immunization, vaccines/ 3 comments

The rollout of COVID-19 vaccinations is picking up speed. Many more people are eligible to be vaccinated now compared to a week or two ago. (You may not be able to get an appointment yet, but hopefully that will get easier soon.) In our recent article about COVID-19 vaccines, we described what mRNA vaccines are, how they work, and how effective they are. But concerns about safety may still have you wondering if you should take your place in line. Let's get to some of your questions about side effects and safety of these vaccines so you can feel confident making a decision that's right for you..

Measuring adverse effects

Medical researchers work hard to design studies that accurately determine side effects of medicines and vaccines. We all know that if you randomly chose 10,000 people and followed them closely, you'd find that during the first week some would develop a headache, a fever, or feel unusually tired. Over several weeks some would notice muscle or joint pain for some reason. Over the course of months some might even suffer a heart attack, stroke, or other health problem. Some would even die. That's the natural course of things. When 10,000 people get a new vaccine, many of them will suffer those same problems. They might blame the vaccine. But was the vaccine really the cause? How can we know?

Well, researches find another group of 10,000 randomly chosen people, and give them an injection without vaccine. They follow both groups in exactly the same way and document reported problems. If people in the vaccine group report a symptom more often, the vaccine probably caused it. But if the same number of people in both groups report the symptom, it probably didn't. The Pfizer and Moderna studies both used that type of design. Researchers will follow the groups for two years to learn as much as possible. Here's what we know so far.

Side effects

The mRNA COVID-19 vaccines appear to cause many of the same side effects that are common with other vaccines. People reported local (injection site) reactions like pain, redness, and swelling, and systemic side effects like mild fever, chills, muscle and/or joint pain, headache, and fatigue. Those who received the Moderna vaccine also reported nausea and/or vomiting fairly often, while those who got the Pfizer vaccine did not. All of these side effects were more common after the 2nd dose of the vaccine. Typically they were limited to about 24-36 hours.

Researches noted that some other adverse effects were reported in both studies. Things like Bell's palsy, swollen or painful lymph nodes, and even appendicitis. But some people who didn't get the active vaccine also reported those events, and the number of reported problems was so small that it's impossible to identify the cause. Researchers will continue to follow study subjects and the general population closely as the vaccine is given to millions of people. With time, the side effect profile of the new vaccines will become clearer.

A small number of people suffered severe allergic reactions, though that's extremely rare. Life-threatening allergic reactions can happen with any vaccine, including the flu shot. Your immunizers will have emergency procedures in place for that possibility. Most COVID-19 vaccination clinics ask (or require) people to remain on premises for 15 minutes after vaccination to watch for a severe reaction. If you have ever had a severe allergic reaction to a food or medication in the past you'll be asked to stick around for 30 minutes. Those who are allergic to ingredients in the vaccine itself will not be candidates for the vaccine at all.

Now that the vaccine is being rolled out to the entire US population, we'll all need to remember that not everything that happens to people who got vaccinated is due to the vaccine. People who receive the COVID-19 vaccine may report health problems, but it'll be up to researchers and statisticians to determine whether those reactions were due to the vaccine or not.

Use in pregnancy and lactation

Pregnant or lactating women were not enrolled in either of the two large efficacy and safety studies. But several study subjects did become pregnant during the study. As of the most recent information available, none of those patients had suffered any problems. But the fact is that those pregnancies haven't come to a close yet. So while all looks well thus far, the small number of cases and the lack of detailed outcomes data means that no one can say for sure how the two mRNA vaccines will affect pregnant patients and their babies. And so far there are no data on lactating women.

However, we know there are very real risks for pregnant women and their babies if they come down with COVID-19. For that reason, the American College of Obstetricians and Gynecologists recommends that pregnant women be offered the vaccine when their priority group becomes eligible. If you are in this situation, consider your risk of infection, your risk of COVID-19 complications (to yourself as well as your child), and compare that to the possible risks from the vaccine. Talking with your doctor may help you make a decision, but you're not required to do that before getting vaccinated. The American Academy of Pediatrics agrees with that approach. 

Will updated information about vaccine safety and efficacy be shared?

The two COVID-19 vaccines currently in use are authorized by FDA for emergency use (EUA). FDA will continue to evaluate new information and reassess the EUAs as more people are vaccinated. Remember last spring when hydroxychloroquine was granted EUA for treatment of COVID-19? Not long after that, FDA withdrew the EUA after new information showed that the risks outweighed the benefits. The EUA withdrawal was widely publicized. That same level of vigilance and publicity will happen with these vaccines. But each of us has a part to play in providing information. Here's how!

You can help provide information about vaccine safety and efficacy!

The COVID-19 vaccines are being rolled out to the general population as quickly as possible. But at the same time, health experts want to make sure that safety and efficacy are monitored. So CDC developed a smartphone-based tool, V-Safe. You'll get a brochure explaining the program when you get your first vaccination, and you can register while you're waiting afterward. It's a quick and easy process. Then you get regular texts asking about potential side effects as well as possible COVID symptoms - responding takes only a minute or two. You'll get a daily text for the first week, then weekly for a few weeks, then a few more times over the year. The idea is to get as many people as possible participating in the ongoing safely and efficacy evaluation of these promising but unique vaccines. You can still sign up even if you already received your first dose of vaccine. I hope you'll join me and participate in this important program!

As always, please leave your questions and comments in the space below, or contact us directly at BetterMyMeds for all your vaccine and medication-related questions!


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About Betty Chaffee

Betty Chaffee, PharmD, is owner and sole proprietor of BetterMyMeds, a Medication Management service devoted to helping people get the maximum benefit from their medications.


  1. This is the message I received from my primary healthcare provider:
    Unfortunately, we don’t have any information regarding public access to the vaccine. It is extremely unlikely that private offices such as the Karle Medical Group will receive the vaccine in 2021 as participants in the process of vaccinating the population of our area. Most likely this will be done through county health departments and large hospitals. Therefore, the best resources at this time are the county health departments.
    Most of the people I know are getting their name put on a list at the local pharmacy. That will probably be a good option for me.

    1. Tony,
      In Washtenaw County, once your priority group comes up you can fill out an online form to make an appointment. Then you get a call to set up an appointment. Not sure how fast it’s going, but it’s going, anyway.
      The independent pharmacy I work with here in Dexter has been told they may not get a shipment of vaccine for a couple of months though. So for those in the last priority group (16-64 years old with no chronic health problems) it may be some time before they can get vaccinated.
      We will all still be wearing masks, washing a lot, and keeping our distance for a while, it seems.

  2. Pingback: Two People, Two COVID-19 Vaccines, Two Final-Dose Stories - BetterMyMeds

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