Yes. The two mRNA vaccines, Pfizer and Moderna, authorized by the U.S. Food and Drug Administration (FDA) and recommended by the Centers for Disease Control and Prevention (CDC), are very safe and very good at preventing serious or fatal cases of COVID-19. The risk of serious side effects associated with these vaccines is very small.

Lisa Maragakis, M.D., M.P.H., senior director of infection prevention, and Gabor Kelen, M.D., director of the Johns Hopkins Office of Critical Event Preparedness and Response, answer questions about the safety of the COVID-19 vaccines.

COVID-19 Vaccine Safety — What We Know

• The Pfizer and Moderna vaccines are strongly recommended as safe and effective at preventing serious illness or death from COVID-19.
• From December 2020 to December 2021, about 470 million doses of COVID-19 vaccine have been given in the U.S.
• Roughly 12 months of data, including data from tens of thousands of participants in clinical trials, show that the vaccines are safe and effective at preventing serious disease or death due to COVID-19.
• Additional shots and boosters are also authorized for those who meet the guidelines.
• mRNA technology used in the Pfizer and Moderna vaccines has been in development for over 15 years.
• The Pfizer and Moderna vaccines received full FDA approval, which means more data show how well that particular vaccine works.
• Due to potential blood clots following administration of the Johnson & Johnson vaccine, the CDC updated its recommendations in December 2021. The CDC noted that the two mRNA vaccines, from Pfizer and Moderna, are preferred over the Johnson & Johnson vaccine.

Are there risks or safety concerns regarding the COVID vaccines?

To help catch risks or safety concerns, the CDC and FDA monitor possible safety issues with the COVID-19 vaccines. This ongoing work has led to revised recommendations for the Johnson & Johnson vaccine and information about rare side effects tied to the Pfizer and Moderna vaccines.

• Johnson & Johnson/Janssen. In December 2021, the CDC updated its recommendations and stated that either of the two mRNA vaccines is preferred over the Johnson & Johnson (J&J) COVID-19 vaccine. The CDC explained that the Pfizer and Moderna vaccines are preferred due to a greater risk for developing rare but severe blood clots, called thrombosis with thrombocytopenia syndrome (TTS), following administration of the J&J vaccine. The CDC noted that there are some situations when a J&J vaccine may still be used, if the recipient understands the risks and benefits of the J&J vaccine. Read about side effects related to the rare blood clot.

At Johns Hopkins Medicine, we offer Pfizer and Moderna vaccines throughout our vaccine clinics.

• Pfizer and Moderna. After observing rare occurrences of myocarditis following the second injection of the Pfizer and Moderna COVID-19 vaccines, the CDC released information for the public. Most of these myocarditis events happened in teens and young adults, and the majority of the cases were mild and cleared up on their own. Read about side effects related to myocarditis.

This review process continues to monitor vaccine safety. Potential risks of COVID-19 vaccines are reviewed and weighed against the benefits of protection that the vaccines offer as well as the known, serious risk of harm due to COVID-19.

What if I got a J&J vaccine? Should I worry about blood clots?

If you received a Johnson & Johnson vaccine more than three weeks ago, you do not need to watch for side effects related to blood clots.

If you received the J&J vaccine within the last three weeks, you should watch for possible symptoms of TTS and get medical help immediately if you have any of the following:

• Severe or persistent headaches or blurred vision
• Shortness of breath
• Chest pain
• Leg swelling
• Persistent abdominal pain
• Easy bruising or tiny blood spots under the skin near the injection site

Is there a risk of an allergic reaction to a COVID vaccine?

According to the CDC, anyone who has a severe allergy (e.g., anaphylaxis) to any of the mRNA vaccine ingredients should not receive this vaccine. The CDC says people with allergies to certain foods, insects, latex and other common allergens can safely receive the COVID-19 vaccine. Those with a history of severe allergic reaction (anaphylaxis) to injectables or other vaccines should discuss the vaccination with their doctor, who can evaluate and assess their risk.

The COVID-19 Vaccines: What you need to know | Las vacunas anticovid-19: información imprescindible

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How was the COVID-19 vaccine developed so quickly?

The relatively quick development of these vaccines does not mean safety measures were skipped. There are several reasons why the COVID-19 vaccines were developed faster than other vaccines:

• The technologies used to develop the COVID-19 vaccines have been in development for years to prepare for outbreaks of infectious viruses. The manufacturing processes were ready very early in the COVID-19 pandemic.
• Countries shared genetic information when it was available about SARS-CoV-2, the coronavirus that causes COVID-19, which gave vaccine developers an early start at finding a vaccine.
• The testing processes for the vaccines didn’t skip any steps, but the vaccine developers conducted some stages of the process simultaneously to gather as much data as quickly as possible.
• Governments gave money to vaccine developers in advance, so the companies had resources they needed.
• Some types of COVID-19 vaccines were created using messenger RNA (mRNA), a new technology that allows a faster approach than the traditional way vaccines are made.
• Social media enabled companies to reach out to and enroll study volunteers, and plenty of people wanted to help, so there were enough research participants to test the COVID-19 vaccines.
• Because SARS-CoV-2 is so contagious and widespread, many volunteers who got the vaccines were exposed to the virus, and with so many exposures, it took a shorter time to see if the vaccines worked.
• Companies began manufacturing vaccines ahead of their authorization or approval so some supplies would be ready if authorization occurred.

What steps are taken to help make sure the COVID-19 vaccines are safe?

Safety is always a top priority as federal agencies work with vaccine manufacturers and independent scientific organizations to develop, study, authorize and approve new vaccines. Here are some of the steps taken for COVID-19 vaccines, as well as other vaccines:

• Careful testing. All vaccines go through clinical trials to test safety and effectiveness. For the COVID-19 vaccine, the FDA set high safety standards for vaccine developers to meet. This graphic from the National Institutes of Health shows the four phases a vaccine goes through before it is released to the public.
• Authorization for emergency use. If a vaccine or medicine is needed to address an emergency situation such as the COVID-19 pandemic, once it is shown to be safe and effective, the FDA can grant it an emergency use authorization (EUA). An EUA allows a vaccine, treatment or medication to be used before the formal FDA approval.
• Continuous monitoring for problems and side effects. Once a vaccine gets an EUA and is being given to people, the FDA and the CDC continue to watch carefully in case problems arise. Data on the vaccine’s safety record accumulates over time, as more and more people who receive it report on their experience and any side effects. One important way to report adverse events after vaccination is through the Vaccine Adverse Event Reporting System.

Learn more from the CDC about the safety steps for the COVID-19 vaccine.

Demographics of the COVID-19 Vaccine Trials

Do I still have to wear a mask if I get a vaccine?

The CDC continues to monitor the spread of COVID-19 and makes recommendations for wearing face masks, both for those who are fully vaccinated as well as people who are not fully vaccinated.

The CDC also recommends that masks and physical distancing be required when going to a doctor’s office, hospital or long-term care facility, including all Johns Hopkins hospitals, care centers and offices.

Johns Hopkins Medicine’s mask safety guidelines have not changed, and we still require everyone to wear masks inside all of our facilities.

Can I get COVID-19 from the vaccine?

You cannot and will not get COVID-19 from any of the vaccines. The COVID-19 vaccines do not have any virus or other infectious material in them.

What about the safety of COVID-19 vaccination for diverse groups of people?

The FDA and other reviewers closely consider diverse populations and include them in the trials. The clinical trials for the first two COVID-19 vaccines included members of underrepresented minorities and older age groups, and people with conditions such as obesity, diabetes, and heart and respiratory conditions.

Does Johns Hopkins Medicine recommend that I get a COVID-19 vaccine?

Yes, we recommend that everyone who is eligible get vaccinated with one of the currently authorized mRNA COVID-19 vaccines: Pfizer or Moderna. We view both as highly effective in preventing serious disease, hospitalization and death from COVID-19 (including disease caused by the very contagious delta and omicron variants of the coronavirus), and we believe that their benefits outweigh their risks.

At Johns Hopkins Medicine, we offer Pfizer and Moderna vaccines throughout our vaccine clinics.