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What is a COVID-19 vaccine ‘breakthrough’ case?

Tara Gallion injects the Moderna COVID-19 vaccine to Eddie Williams at the Delta Health Center in Mound Bayou, Mississippi. January 30, 2021
Image Credit: NYT

What is the COVID-19 vaccine breakthrough?

This is when a fully vaccinated person becomes infected with the coronavirus. A small number of such cases are expected, and health officials say this is not cause for concern.

COVID-19 vaccines work by training the body to recognize the virus. So if you’ve been exposed to it after being vaccinated, your immune system should be ready to take action and fight it.

In studies, Pfizer and Moderna’s two-dose COVID-19 vaccines were approximately 95% effective in preventing disease, while Johnson & Johnson’s single-dose vaccine was 72% effective, although direct comparisons are difficult. Thus, while vaccines protect us very well from the virus, it is still possible to get infected with mild or no symptoms, or even get sick.

If you end up getting sick despite being vaccinated, experts say the injections are very good at reducing the severity of the disease – the main reason for getting vaccinated.

“Most people with breakthrough infections get mild illness,” said Dr. William Moss, vaccine expert at Bloomberg Johns Hopkins School of Public Health.

In the United States, people who have not been vaccinated are responsible for nearly all hospitalizations and deaths from COVID-19.

It is difficult to determine why this or that breakout occurs. Moss said the amount of virus you are exposed to may be a factor. Our individual immune system also affects how well we respond to injections. Some people, for example, have health problems or are taking medications that can reduce the sensitivity of their immune systems to vaccines.

People could also have been exposed to the virus before the shots had fully worked. Although less likely, they may have received a dose that was incorrectly stored or injected, Moss said.

The Centers for Disease Control and Prevention notes that options may be factors in some breakthrough cases, although so far evidence suggests that vaccines used in the US are protecting against them.

Health officials are also watching for signs of rising cases, which could signal that vaccine protection is waning and boosters are needed.

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