Are You Protected If Your COVID-19 Vaccine Didn't Cause Side Effects?

You might be the type of person who begins preparing for your COVID-19 vaccine in advance of your appointment. You try to get a full workout in, make sure you have some Tylenol on hand, and buy chicken noodle soup, saltine crackers, and ginger ale—all in an effort to make yourself as comfortable as possible for any impending side effects from the vaccine.

All four of the COVID-19 vaccines authorized or approved for use in the US by the US Federal Food & Drug Administration as of August 2022—Pfizer-BioNTech, Moderna, Novavax, and Johnson & Johnson—can cause any combination of the following symptoms in adults ages 18 and older:

• Pain, swelling, or redness at the injection site
• Fatigue or tiredness
• Headache
• Muscle pain
• Fever and chills
• Nausea

These symptoms tend to be mild and only last for a few days. What you feel will likely not vary much with follow-up doses and boosters, but you probably won't get the same side effects as those around you. Overall, COVID-19 vaccines produce reactions similar to those of other routine vaccinations, per the CDC.

What if You Don't Have Any Side Effects?

The CDC specified: "Even if you don't experience any side effects, your body is building protection against the virus that causes COVID-19."

"While it's true that vaccine side effects are often attributed to the vaccine 'taking' or prompting a reaction if they are not experienced, it doesn't mean one is not sufficiently protected by the vaccine," Amesh A. Adalja, MD, senior scholar at Johns Hopkins Center for Health Security, told Health. "Each person's immune system has some idiosyncrasies that could be at play."

"Everyone is different," added Richard Watkins, MD, infectious disease physician, and professor of internal medicine at Northeast Ohio Medical University. "So just because you have no symptoms after the vaccine doesn't mean there is a problem," Dr. Watkins told Health.

Clinical Data About Vaccine Side Effects

Post-vaccine symptoms can be divided into local (injection site) and systemic (whole-body) reactions. Here's how likely people were to experience those in vaccine trials.

As of August 2022, Pfizer was the most commonly received vaccine in the US, per CDC data. When it comes to local effects, the most common one in Pfizer trials was pain where you got the shot. About 83% of people ages 18–55 reported pain after the first dose of the Pfizer vaccine in trials, and 78% after the second dose.

People older than 55 were less likely to experience the pain—71% of them felt it after the first dose of the Pfizer vaccine and 66% after the second dose. This is according to a review published in the journal Human Vaccines & Immunotherapeutics.

Systemic side effects were more common after the second Pfizer shot. The most commonly reported systemic side effect in Pfizer trials was fatigue. About 59% of people aged 18–55 reported this symptom after the second dose. People older than 55 were less likely to experience this side effect—about 51% reported fatigue. The next most common systemic side effects were headaches and muscle pain.

People in the Moderna vaccine trials were more likely to experience injection site pain, fatigue, headaches, and muscle pain after the second shot, per the February 2022 review. People in the Johnson & Johnson trials were less likely to experience injection site pain, fatigue, and headaches, but slightly more likely to feel muscle pain.

Across all three vaccines, people who were older (65 and older in Moderna trials and 60 or older in Johnson & Johnson trials) were less likely to experience side effects.

Novavax was authorized in the US more recently than the other three vaccines available as of August 2022. About 81% of people aged 18–64, and about 61% of people 65 and older, in Novavax trials, experienced injection site pain after the second dose.

Fatigue was the most commonly reported systemic side effect after the Novavax vaccine, with about 58% of people ages 18–64, and about 35% of people 65 and older, reporting it after the second dose.

What To Expect After the COVID-19 Vaccine

To summarize, here's what to know about the side effects of COVID-19 vaccines in general:

• Not everyone experiences side effects—reactions to COVID-19 vaccines vary.
• Injection site pain is the most common local side effect across all four vaccines approved as of August 2022. Fatigue is the most common systemic side effect, followed by headaches and muscle pain.
• You're more likely to experience side effects after the second dose.
• You're less likely to experience side effects if you are in an older age group (with "older" defined differently for different vaccines).
• Side effects tend to be mild and go away within a few days.
• COVID-19 vaccine side effects are similar to those of other routine vaccinations.

"Every person reacts differently to the vaccine, just like they do when exposed to COVID-19, and the response is somewhat unpredictable in any individual," Lewis S. Nelson, MD, professor, and chair of the Department of Emergency Medicine, and director of the Division of Medical Toxicology at Rutgers New Jersey Medical School, told Health.

And just because someone has a strong response to the vaccine doesn't necessarily mean they've acquired more protection—it just means they had more of an inflammatory response as their bodies crafted protective immunity, William Moss, MD, executive director of the International Vaccine Access Center at Johns Hopkins Bloomberg School of Public Health, told Health.

"People who don't have any side effects are just as likely to be protected as people who have severe side effects," Dr. Moss said.

A Quick Review

The bottom line here: If you didn't feel any side effects after your COVID-19 vaccine, it's not something to worry about—you'll still have the same protection as someone who had to stay in bed the day after they get the shot.

There's no need to worry if you feel fine the next day. But note that, however you feel, vaccines may not fully protect you until a week or two after you get the final shot in your primary vaccine series (after two shots for Pfizer, Moderna, and Novavax, and after one shot for Johnson & Johnson).

While your body builds protection, follow the CDC-recommended precautions based on the COVID-19 level in your community. And remember: No vaccine is 100% effective, so continue checking those CDC guidelines, which may change over time.

If you do get side effects and are worried, don't hesitate to talk to a healthcare professional. And to contribute to ongoing vaccine safety monitoring, you may also report your symptoms through a simple smartphone tool called v-safe or the Vaccine Adverse Event Reporting System (VAERS).

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.