What breakthrough infections mean for the Covid vaccines

A number of new coronavirus infections among vaccinated athletes and government officials have drawn attention to an apparent increase in what are known as breakthrough infections. But while the cases of fully vaccinated people have increased in the past few weeks, experts say there is little to worry about.

A July 15 game between the New York Yankees and the Boston Red Sox was postponed due to several confirmed breakthrough cases. A few days later, Kara Eaker, a deputy of the US women’s gymnastics team who was vaccinated in May, tested positive at an Olympic training camp in Japan. And this week, government officials announced that a White House employee and senior communications advisor to House Speaker Nancy Pelosi, D-California, tested positive despite being fully vaccinated. The cases came after six members of a Texas Democratic delegation in Washington, DC, tested positive

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More than 161 million people in the US have been fully vaccinated, according to the Centers for Disease Control and Prevention, and breakthrough infections appear to be a tiny fraction of them.

However, as the pandemic continues and more transmissible variants of the virus become widespread, the number of breakthrough infections is expected to increase. However, studies have shown that most cases in vaccinated people are mild – if a person develops symptoms at all – and research shows that vaccines still offer strong protection against the known variants.

“The reality is that many of these breakthrough infections have been vaccinated and tested positive, but there is a difference between a positive test and illness,” said Angela Rasmussen, virologist with the Vaccines and Infectious Diseases Organization at the University of Saskatchewan Canada .

In other words, people who test positive may have tiny amounts of the virus in their bodies – enough to be detected with Covid-19 tests, but not enough to make them sick.

And because the vaccines strengthen the immune system, it can detect and fight invading pathogens more quickly.

“If you have a lot of good antibodies, they can potentially attach to the virus before it can cause problems, and that can decrease or decrease your chances of getting sick,” said Dr. Robert Darnell, senior physician and biochemist at Rockefeller University in New York.

However, breakthrough infections are expected as no vaccine is 100 percent effective. In rare cases, fully vaccinated people can become seriously ill and die from Covid-19, but the vast majority of breakthrough cases have been mild or asymptomatic.

That’s because the vaccines act like screens to keep most – but not necessarily all – of the virus particles from entering the body. Various factors affect the strength of the screen and how many tiny virus particles can cross the barrier, said Dr. Sarah Fortune, an immunologist at Harvard TH Chan School of Public Health.

A health worker administered a Pfizer Covid-19 vaccination at a mobile vaccination clinic in Los Angeles on July 16, 2021.Irfan Khan / Los Angeles Times via Getty Images

“These variations are easier to transfer, so they come through the screens better,” she said. “The other factor is how many viruses out there are trying to get in, and that’s determined by the vaccination rates in your community. It’s how many viruses you’re exposed to.”

Vaccines can also lower the amount of virus in the body, which can limit the ability of people with breakthrough infections to pass them on to others, although the effects are not yet well understood. More research is needed to assess the impact that asymptomatic breakthrough cases in particular have on transmission.

“It may be that the vast majority of vaccinated people who become infected simply don’t make enough virus to infect another person,” said Dr. Janko Nikolich-Žugich, immunologist and professor of medicine at the University of Arizona.

Darnell of Rockefeller University said the recent surge in breakthrough infections has not been linked to a similar surge in hospital admissions or deaths, which is encouraging evidence that vaccines seem to be holding up well despite new and emerging variants.

The CDC initially tracked all breakthrough infection cases, but began focusing on the 1. At that point, more than 100 million people in the US were fully vaccinated and the CDC counted more than 10,000 breakthrough infection cases.

On July 12, the CDC reported 5,492 landmark cases in which patients were hospitalized or died. Three quarters of the cases were in people over 65. Although they are tracked as breakthrough infections, it is not necessarily that Covid-19 caused the hospital admissions or deaths, especially in patients who were asymptomatic.

Rasmussen said higher hospital and death rates among older adults are not surprising as older people are generally more susceptible to serious illness from Covid-19. Immunocompromised people or those with underlying diseases have a similarly higher risk.

In Israel, where 80 percent of people aged 16 and over were fully vaccinated, researchers looked at 152 groundbreaking cases of hospitalized patients and found that most people with underlying conditions such as high blood pressure, diabetes and congestive heart failure were affected. The study, published July 6 in the journal Clinical Microbiology and Infection, found that only six cases involved patients with no comorbidities.

Israel reported this month that the Pfizer BioNTech vaccine was 93 percent effective in preventing hospitalizations and serious illness, but its effectiveness in preventing infection and symptomatic illness fell to 64 percent.

A separate analysis published June 25 by Public Health England found that two vaccinations of the Pfizer BioNTech and AstraZeneca vaccines were 79 percent effective against symptomatic delta disease and 96 percent effective against hospitalization .

The ability of vaccines to protect against serious illness is vital, Rasmussen said, and an indication that vaccinations will continue to work well.

“If we saw the intensive care units fill up with fully vaccinated people, it would be an indication that the vaccines are no longer effective,” she said.

Although the vaccines remain highly effective, there is cause for concern if the outbreaks continue to smolder across the country. The more the virus can circulate, the greater the chance that the pathogen will mutate to become more transmissible, cause more serious diseases, or escape vaccine protection.

“Any pathogen arms race ends badly because that’s basically evolution,” said Fortune. “What we mean is that the virus is trying not to go extinct, and evolution will favor transmission. Evolution will encourage the escape of vaccines. “

To prevent such a result, one must focus on vaccinating as many people as possible in the US and around the world.

“I lose infinitely more sleep because we have so many unvaccinated people who are at an enormous risk of developing serious diseases,” said Nikolich-Žugich. “We shouldn’t be complacent or awkward, but it pales in comparison to how we get as many people as possible vaccinated.”

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