What is a COVID breakthrough case and does this change our confidence in the vaccines?

Breakthrough cases occur when a person who has been vaccinated against an illness contracts that illness.

Breakthrough cases are not unique to the COVID-19 vaccine and are inevitable, given that no vaccine is 100 percent effective. COVID-19 vaccines remain highly effective and vaccinated individuals are far less likely than unvaccinated individuals to contract COVID-19.

As more people are vaccinated, chances are greater that we will hear about more breakthrough infections. These cases still represent a very small fraction of the total number of people who are fully vaccinated.

The purpose of a vaccine is to reduce both the chances of getting a disease and, among those who experience infection, to reduce the negative outcomes of the disease. In the case of COVID-19, the goals are as follows: 1) reduce transmission altogether and 2) if transmission does happen, limit the severity of symptoms and significantly reduce hospitalizations and deaths from COVID-19.

The vaccines approved or authorized by the FDA accomplish these goals. Fully vaccinated people are much less likely than unvaccinated people to become sick with COVID-19 and are much less likely to experience severe illness and death.

The CDC and FDA continue to monitor how well the vaccines protect vulnerable people from illness and have begun to recommend supplemental vaccination or booster shots for some people. This does not indicate vaccines are not effective. Immune responses to many different vaccines can wane with time and additional doses can help bolster that response and extend protection.

Ensuring that anyone who is unvaccinated gets vaccinated as soon as possible is key to slowing transmission in the unvaccinated population and reducing the amount of virus circulating among all people, further reducing the chances anyone is exposed to the virus.