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Vaccinated: What you need to know about breakthrough infections

There's no doubt that COVID-19 vaccines work. And all those shots going into arms? They are making a difference. But some fully vaccinated people have still gotten sick with COVID-19. How can that happen?

Experts call these "breakthrough cases," and they are not common. As of August 9, 2021, more than 166 million people in the U.S. had been fully vaccinated. Of these, there were only 8,054 COVID-19 hospitalizations or deaths reported to the Centers for Disease Control and Prevention (CDC) by 49 states. (On May 1, CDC shifted to monitoring breakthrough cases only in which someone was hospitalized or died.)

The fact that some breakthrough cases exist is not unusual, CDC notes. In fact, this occurs with all vaccines. Clinical trials and observations show that vaccines are very safe and highly effective. But no vaccine is 100% perfect. So even with a vaccine that prevents more than 90% of infections, a small number of people will still get sick.

Breakthrough cases can also happen for other reasons. For instance:

1. A person could be exposed to the virus just before or after they are vaccinated. It takes about two weeks after the final dose for the body to build immunity to the coronavirus. Only then are you considered fully vaccinated. If you're exposed during that time, you could still get sick.

2. Variants might account for some breakthrough cases. Some variants of the coronavirus may spread more easily. COVID-19 vaccines still seem to work against most of these variants. But it's possible some might be better at overcoming vaccine immunity.

CDC continues to look into reports of breakthrough cases. But so far, they don't seem to happen more often to people who share common risk factors.

Our best shot at beating COVID-19

Getting vaccinated will make you much less likely to get COVID-19. And if you are one of the few vaccinated people who still gets the disease? There is evidence that COVID-19 vaccines may make your illness less severe.

Check out CDC's latest advice on mask use and safe activities for fully vaccinated people at

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This information is provided for educational purposes only. Individuals should always consult with their healthcare providers regarding medical care or treatment, as recommendations, services or resources are not a substitute for the advice or recommendation of an individual's physician or healthcare provider. Services or treatment options may not be covered under an individual's particular health plan.