COVID Vaccine Breakthrough Cases Explained As People Catch Virus After Shot

Health officials in Washington have announced they are investigating reports of COVID "breakthrough cases," as similar incidents are recorded across the U.S.

"Breakthrough cases" refer to people who catch a virus despite having received the vaccine for it more than two weeks earlier.

Scientists say the incidents are rare, but are to be expected in mass vaccination programs. Although vaccines have been shown to prevent COVID illness in clinical trials, they are not 100 percent effective.

In a statement released on Tuesday, Washington's Department of Health said 1 million people in the state had been fully vaccinated. Of these, there was evidence that 102 had caught COVID afterwards.

Most of the 102 breakthrough cases, which were identified since February 1, showed mild or no symptoms. Eight people were hospitalized, however.

Umair Shah, Washington's secretary of health, said in a statement: "It is important to remember that every vaccine on the market right now prevents severe disease and death in most cases.

"People should still get vaccinated as soon as they are eligible, and encourage friends, loved ones and co-workers to do the same."

The Minnesota Department of Health revealed on March 2 that it was also investigating COVID breakthrough cases.

The department said self-isolation was recommended in these cases "until 10 days have passed since symptom onset (or test date for asymptomatic cases), symptoms are improving, and patient has been afebrile [fever-free] for at least 24 hours without fever-reducing medication."

Similar cases have been reported in Florida. Dr Sunil Joshi, president of the Duval County Medical Society Foundation, told Jacksonville news outlet News4Jax that breakthrough cases could also occur with flu.

He said: "It's like the flu shot, for instance, right. We know, we encourage people to get the flu vaccine. That doesn't mean that you're not going to get the flu. But the disease is significantly lessened.

"So remember, the whole goal for this, from the very beginning, has been to keep people out of the hospital. And so anything positive after the vaccine is not unusual, it can happen."

Matt McQueen, director of epidemiology for the pandemic response office at the University of Colorado Boulder, said in a February vaccine Q&A that it was "possible, but unlikely" for people to get COVID after having received the vaccine.

"Early evidence suggests that in the rare case that someone is infected after being fully vaccinated, they experience a milder course of illness than they would have otherwise," he added.

More than 150 million doses of COVID vaccine have been administered across the U.S. according to the latest figures from the U.S. Centers for Disease Control and Prevention.

COVID vaccine being given
A doctor receives the Pfizer-BioNTech vaccine on December 15, 2020, in Miami. It is unlikely but not impossible for people to catch COVID after getting the shot. Joe Raedle/Getty