COVID-19 Vaccine Side Effects and Safety

It is not uncommon to experience side effects after getting the COVID-19 vaccine, most of which are relatively mild and short-lived. These commonly include side effects you might experience with other vaccines, such as injection site pain, fatigue, and flu-like symptoms.

The side effects (and risk of side effects) can vary based on the type of vaccine you are given and whether this is your first or subsequent shot. Many people who receive a COVID vaccine experience no side effects.

Although there is a risk of severe side effects, including heart inflammation and anaphylaxis, the risk is considered small compared to the benefits. According to research from Columbia University, COVID-19 vaccination in the U.S. averted no less than 8.3 million infections, 681,000 hospitalizations, and 118,000 deaths from 2021 to 2022.

What Are the Common Side Effects of COVID-19 Vaccines?

As of 2024, there are three COVID-19 vaccines approved for use by the U.S. Food and Drug Administration (FDA):

• Pfizer-BioNTech (marketed under the brand name Comirnaty), an mRNA vaccine
• Moderna (marketed under the brand name Spikevax), also an mRNA vaccine
• Novavax, a protein subunit vaccine

Although mRNA vaccines (which deliver genetic instructions to the immune system on how to build protective antibodies) and protein subunit vaccines (which expose the immune system to harmless, manufactured proteins that mimic COVID-19) work differently, their common side effects are similar.

How Quickly Do Side Effects Develop?

In the same way that some people experience side effects from COVID vaccines and others don’t, the timing of side effects, if any, can also vary.

For most, side effects tend to appear within 14 hours of the first vaccination and slightly longer for subsequent vaccinations.

In a very small group of people, side effects may occur within minutes. An immediate reaction is troubling as it may be the sign of a potentially life-threatening, whole-body allergy known as anaphylaxis. The sooner a reaction occurs, the more likely this will be.

With anaphylaxis, a person will experience a spontaneous outbreak of rash or hives accompanied by breathing difficulties, abnormal heart rhythms, and dizziness or lightheadedness. If not treated as a medical emergency, anaphylaxis can lead to shock, coma, and even death.

This is why healthcare providers will often ask you to wait 15 minutes after vaccination before leaving so that treatment can be dispensed if anaphylaxis symptoms occur.

Even so, the risk of this occurring is relatively small. While as many as 2% of people who get a COVID vaccine will experience a rash, only a very small proportion will experience anaphylaxis. According to a 2023 study from Harvard Medical School, the rate of anaphylaxis among COVID vaccine recipients is roughly five cases out of every million doses.

How Long Do Side Effects Last?

Following COVID vaccination, side effects, if any, tend to last one to three days.

Symptoms severe enough to require missing work or school are uncommon. A 2021 study from the Mayo Clinic reported that the rate of absenteeism among healthcare workers who received the COVID vaccine was 4.1%.

Side effects can persist longer than this, though it is uncommon for these to last more than a week or two. In rare cases, a person may develop long post-COVID vaccination syndrome (LPCVS), defined as side effects lasting for more than four weeks in the absence of any other explanation. Some cases have been reported to last as long as 11 months.

Symptoms typically include persistent headache, joint pain, muscle cramps, insomnia, visual disturbances, and “brain fog.”

Even so, LPCVS is thought to be rare. To date, few cases have been reported in the medical literature.

How Common Are Side Effects From COVID-19 Vaccines?

In the early part of the pandemic, most people experienced side effects from the vaccines. This was largely due to the fact that people were exposed to the vaccines for the first time and would almost invariably have a stronger immune reaction. Certain vaccines that are delivered in one dose today were given in two doses then.

At that time, up to 77% experienced side effects after the first dose and up to 86% after the second dose. The majority had low-grade side effects, like fatigue and fever.

Today, the rate of reported side effects is relatively modest. Based on a review of data from the Centers for Disease Control and Prevention (CDC) and the Vaccine Adverse Events Reporting System (VAERS), the most common side effects experienced by people in the U.S. were headache (15.7%), fever (13.6%), and fatigue (13.5%),

Of the three available vaccines, Novavax is the only one to require two doses in adults and children 12 and over.

Severe Side Effects and Complications

In addition to a risk of anaphylaxis, the other potentially severe side effects are myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the outer lining of the heart).

These side effects are mainly seen in males age 12 to 40. Although the exact cause of these is poorly understood, most cases occur within seven days of receiving a second dose of an mRNA COVID-19 vaccine (Comirnaty or Spikevax).

There is also some evidence that vaccination with the Novavax protein subunit vaccine might increase the risk of this side effect.

Myocarditis and pericarditis are rare, and occur more often in people infected with COVID than in those who get vaccinated, meaning the benefits of the vaccine outweigh the risks:

• Rate in non-infected people: 1 to 10 cases per 100,000 people
• Rate in those who receive the vaccine: 10 to 50 cases per 100,000 people
• Rate in those with COVID infection: 150 cases per 100,000 people

Moreover, most cases are relatively mild and transient.

Myocarditis and pericarditis are characterized by the sudden onset of flu-like symptoms accompanied by:

Symptoms of vaccine-induced myocarditis or pericarditis typically require hospitalization to monitor for rare but potentially deadly complications like cardiac arrhythmia (irregular heartbeats) and cardiac arrest (in which the heart suddenly stops beating).

With that said, most people respond well to rest and medications like colchicine, steroids, or nonsteroidal anti-inflammatory drugs (NSAIDs).

Summary

Common side effects of COVID-19 vaccines include injection site pain, fatigue, muscle aches, joint pain, fever, and headaches. Most cases are mild, developing within 14 hours of the injection and resolving within one to four days. Severe side effects are rare.

The current body of evidence suggests that the benefits of COVID-19 vaccination outweigh the potential risks.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.