A breakthrough infection is an infection with a virus, bacterium or other germ after you have been vaccinated. This is an expected occurrence for a small percentage of those receiving any vaccine, since no vaccine for any disease is 100% effective in preventing infection in every person who receives it.

Breakthrough coronavirus infections happen when someone who has been fully vaccinated for COVID-19 becomes infected with the SARS-CoV-2 coronavirus. 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, explain what you need to know about breakthrough coronavirus infections.

Can you get COVID after being vaccinated?

Yes. Breakthrough COVID-19 cases happen in people who are fully vaccinated, and they seem to happen more frequently now that the delta variant is circulating widely and immunity may be waning among those who got the vaccine many months ago. All three available coronavirus vaccines are very good at protecting you against severe forms of COVID-19, but they are not 100% effective in preventing infection. Breakthrough COVID can be caused by the delta variant, which is more contagious than some other coronavirus variants.

How common are breakthrough cases of COVID?

A study in Washington state gathered data from over 4 million fully vaccinated people. The data showed a rate of about 1 in 5,000 experienced a breakthrough infection between January 17 and August 21, 2021. More recently, some populations have shown breakthrough infection rates of approximately 1 in 100 fully vaccinated people.

Is coronavirus after vaccination dangerous?

Breakthrough coronavirus infections can cause mild or moderate illness, but the chances of serious COVID-19 are very low, especially for people who are not living with a chronic health condition.

The COVID-19 vaccines are very effective in keeping you from having to go to the hospital, being put on a ventilator or dying due to severe coronavirus disease, including COVID caused by the delta coronavirus variant.

The Centers for Disease Control and Prevention (CDC), as well as Johns Hopkins Medicine and other health care organizations, recommend COVID-19 vaccines for everyone 12 years old and over.

What are the symptoms of COVID after vaccination?

The symptoms of breakthrough COVID-19 are similar to COVID-19 symptoms in unvaccinated people, but are generally milder. You may not notice any symptoms at all.

If you are fully vaccinated and develop a fever, feel ill, or experience any symptom that is not typical for you, getting a COVID-19 test may be a good idea.

For instance, if your allergies seem worse than usual or you experience a headache or mild cough when you normally don’t have one, talk to your doctor about being tested for COVID-19.

If you suspect you might have breakthrough COVID-19 keep in mind that if you are infected, you can transmit the coronavirus to another person. While you are waiting to be tested or to get your test results, isolate yourself from others to the extent possible and follow coronavirus precautions such as mask wearing, physical distancing and hand hygiene to protect those around you.

Who is most at risk for breakthrough COVID-19?

Although any fully vaccinated person can experience a breakthrough infection, people with weakened immune systems caused by certain medical conditions or treatments (including organ transplants, HIV and some cancers and chemotherapy) are more likely to have breakthrough infections.

The CDC recommends that patients with weakened immune systems receive an additional, or third, dose of the COVID-19 vaccine 28 days or later after their second shot to strengthen their protection against the coronavirus. 

Ask your doctor if you are living with a medical condition or receiving treatment that puts you at risk for a lowered immune system, and if getting a third vaccine is appropriate.

Am I at risk for “long COVID” if I get a breakthrough coronavirus infection?

At least one large study suggests that being vaccinated reduces the chance that you will end up with lingering symptoms of COVID-19, sometimes referred to as “long COVID.”

How can I prevent breakthrough coronavirus infection?

We advise that even fully vaccinated people continue to follow all safety precautions (masking, distancing and hand hygiene) while the COVID-19 pandemic continues.

Immunocompromised patients should contact their doctors and discuss getting a third dose of the coronavirus vaccine.

The CDC recommends boosters for certain groups of people. A COVID booster is an additional dose of the COVID-19 vaccine that can help maintain your immunity for longer if the protection of your initial vaccine(s) has begun to decline over time. Getting a booster may help prevent a breakthrough infection or having symptoms.

Avoid indoor gatherings, especially when many people are present, mask-wearing is inconsistent, or ventilation is poor.

The basic coronavirus precautions are effective in lowering your chances of becoming infected with the coronavirus, even after you have been fully vaccinated.