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People wait in line for a COVID-19 vaccine. Paul Bersebach/Orange County Register via Getty Images
  • While COVID-19 vaccines are a vital part of the path out of this pandemic, they’re not fail-proof.
  • Rare cases of “breakthrough” infections have been reported in multiple states.
  • Experts say understanding these breakthrough cases will help them monitor how effective the vaccines are in the real world, and monitor whether booster shots will be needed.

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The number of people being vaccinated against COVID-19 is increasing every day in the United States. On average, more than 2.8 million people are being vaccinated against the disease every day.

While vaccines are a vital part of the path out of this pandemic, they’re not fail-proof. In rare cases, officials are reporting “breakthrough” infections.

In these rare cases, people can still develop COVID-19 despite vaccination.

But experts say these rare cases are expected as more people get vaccinated, and they may ultimately help officials stamp out the coronavirus.

A breakthrough case is when someone develops an illness despite already being fully vaccinated.

This isn’t a reason to avoid getting vaccinated. There’s no vaccine that can provide 100 percent immunity against any disease.

Experts say these rare breakthrough COVID-19 cases will give experts a way to determine the extent to which COVID-19 vaccines work and what coronavirus variants may be causing these cases despite vaccination.

“I don’t think we need to be overly concerned as of yet,” said Dr. William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University in Nashville, Tennessee.

“We should know that these vaccines are not perfect, and under ideal circumstances they provide up to 95 percent chance of protection. Not everyone, particularly those that are frail and partly immunocompromised, may not even get 95 percent protection,” he said.

Additionally, while a COVID-19 vaccine isn’t completely protective against symptoms, experts stress the vaccine is extremely effective at preventing the most serious complications that lead to hospitalization and death.

In clinical trials, people given COVID-19 vaccines were not hospitalized even in rare cases of developing the disease.

Fully vaccinated people have some immunity against COVID-19, particularly against the strain of the coronavirus the vaccine was made for.

And while COVID-19 vaccines have some protection against several of these variants, it doesn’t give full immunity — particularly in people who may be immunocompromised.

“Most people will mount a strong immunologic response. But individuals who are highly immunocompromised may have a more blunted response, and these individuals need to remain careful even if they are vaccinated,” said Dr. David Hirschwerk, attending physician in the department of infectious diseases at Northwell Health in Manhasset, New York.

All of this is expected.

People who are immunocompromised don’t always mount the strongest response to vaccines.

And even people who aren’t immunocompromised can still be vulnerable to breakthrough cases.

Experts say researching these breakthrough cases will be key in understanding the real-world effectiveness of COVID-19 vaccines and the likelihood a coronavirus variant may be able to evade vaccine protection.

“Scientists can study any trends and predictors of which individuals may be less protected from vaccination,” Hirschwerk said.

Researchers will be studying which groups of people get these breakthrough cases, how frequently they occur, where they occur, and the genetic sequencing of breakthrough variants to figure out how to best fight back against COVID-19.

Schaffner pointed out that by studying breakthrough cases, scientists can monitor for troubling signs of rising variants.

“By understanding variants we are able to understand how commonly these phenomena are occurring,” Schaffner said of breakthrough cases. “And if they are preferentially being caused by variants, we may need a booster dose that protects against those strains.”

The Centers for Disease Control and Prevention (CDC) is continuing to assess how COVID-19 vaccines are working in real-world conditions.

Experts will also closely watch what happens when vaccinated people develop COVID-19 and what their symptoms are like.

“The majority of these will very likely be of people with mild to moderate symptoms,” Hirschwerk told Healthline.

Breakthrough infections are an expected outcome in any vaccination process. No vaccines is 100 percent fail-proof.

These breakthrough cases aren’t a reason to panic. Instead, experts say they show why we still need to practice mask wearing, handwashing, and physical distancing measures while scientists learn how and why these cases are occurring.

And most importantly, these breakthrough cases shouldn’t deter the public from getting vaccines, as they do work.

COVID-19 vaccines remain extremely effective in preventing severe and life threatening cases of COVID-19.

Rajiv Bahl, MD, MBA, MS, is an emergency medicine physician and health writer. You can find him at