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Breakthrough COVID-19 cases expected to become more common in coming months

Experts blame delta variant’s rise and declining efficacy of vaccines but say most infections among the vaccinated will be mild

A health care worker conducts a COVID-19 test at a walk-up location in Farragut Square in Washington on Sept. 3.
A health care worker conducts a COVID-19 test at a walk-up location in Farragut Square in Washington on Sept. 3. (Tom Williams/CQ Roll Call file photo)

Mild cases of COVID-19 among vaccinated individuals are becoming increasingly common as the highly contagious delta variant barrels through communities, but physicians and public health experts say that shouldn’t be a cause for significant concern.

A breakthrough case of COVID-19 occurs when a person contracts COVID-19 at least two full weeks after the final dose of the vaccine. The Centers for Disease Control and Prevention tracks only breakthrough cases that result in hospitalization or death, as these incidences are both serious and very rare.

COVID-19 cases are up to five times more common in unvaccinated individuals compared with the vaccinated, according to the CDC. But state-level data shows that milder breakthrough cases that do not result in hospitalization are on the rise among the fully vaccinated as virus transmission increases and vaccine efficacy decreases. And they’re expected to keep increasing.

“It’s likely that everybody will probably get infected with COVID-19 [at some point] because it’s an endemic respiratory virus. The goal is to make sure that at that time, that infection occurs after you’ve been vaccinated so it’s mild,” said Amesh Adalja, a doctor and infectious disease specialist at Johns Hopkins Center for Health Security.

A mild breakthrough infection counts as any case of COVID-19 in a fully vaccinated person that does not require hospitalization. Fortunately, these are the vast majority of breakthrough cases, and for some, they are asymptomatic.

But for many otherwise healthy individuals, these so-called mild cases do not feel mild at all.

Fevers, muscle aches, congestion and extreme fatigue are common symptoms of a breakthrough infection, similar to a bad case of the flu. It’s not unusual for a person with a breakthrough infection to feel lingering symptoms for several weeks, but physicians say the worst ailments, such as a hacking cough or searing headaches, usually let up in two weeks or less.

Mild breakthrough cases also require sick individuals to quarantine and stay home from work or school, regardless of their symptoms. Their family members and other close contacts may also have to isolate and monitor symptoms.

The early symptoms of a COVID-19 breakthrough case can often be mistaken for a cold or allergies, leading an infected but unaware individual to potentially spread the coronavirus to others.

Levels of community spread play a key role in how common and how severe breakthrough infections are.

Carlos del Rio, a professor of medicine in the division of infectious diseases at Emory University School of Medicine, compared COVID-19 vaccines in areas of high community transmission to an umbrella in a rainstorm.

“If I’m in a little bit of rain and I have an umbrella, I don’t get wet. But if I’m in a hurricane, I’m going to get wet despite wearing an umbrella. That doesn’t mean you can say, all of a sudden, umbrellas don’t work very well. It’s a hurricane,” del Rio said, explaining why the United States is seeing more mild breakthrough cases.

Rising number of cases 

CDC data released on Sept. 10 counted an average of 10.1 breakthrough cases for every 100,000 fully vaccinated people, meaning that at that time, just 0.01 percent of vaccinated individuals had a breakthrough case. This data was collected between April 4 and July 19.

But state data shows that number is now much higher.

The U.S. saw a spike in COVID-19 cases, hospitalizations and deaths in August and September as the delta variant gained steam. Currently, nearly 95 percent of U.S. counties have high levels of community transmission with more than 100 positive cases per 100,000 people, both unvaccinated and vaccinated, in the past week.

“With a lot more virus circulating — and almost all of it is delta, which is more transmissible — a fully vaccinated person is more likely to be exposed than they were in July, depending on where they live,” said Jen Kates, director of global health and HIV policy at the Kaiser Family Foundation.

The District of Columbia recorded more than 300 breakthrough COVID-19 cases per week throughout August. That is a sharp uptick from June, when it routinely recorded around 10 breakthrough cases per week.

“With an increase in community spread, there are more opportunities to be exposed, and we expect a proportion of vaccinated people will become infected, knowing that our breakthrough rate is 0.72 percent,” a D.C. Department of Health spokesperson said.

Delaware is also tracking breakthrough cases, and as of Sept. 10, the state recorded more than 2,300 breakthrough cases, or roughly 0.5 percent of all Delawareans who have been fully vaccinated.

The Pennsylvania Department of Health found 6 percent of its recorded cases are among fully vaccinated individuals.

Most breakthrough cases will not land you in the hospital, though, or even urgent care. The risk of death and hospitalization remains very low for fully vaccinated individuals.

State data shows vaccines keep people out of the hospital and alive. New Jersey found just 0.002 percent of its vaccinated population died of the virus.

When asked about rising case numbers, CDC communications specialist Kristen Nordlund noted that this is consistent with declining vaccine efficacy and rising case counts with the delta variant.

Post-vaccine immunity wanes over time, according to the CDC. Both the Pfizer and Moderna vaccines appear to lose some efficacy after four months, and the Johnson & Johnson one-shot vaccine is the least effective overall.

Food and Drug Administration advisers recently recommended a Pfizer COVID-19 booster shot for those at highest risk of severe disease if they contract a breakthrough case and are expected to weigh boosters for the Moderna vaccine soon — but it could be a long time before the rest of the population can access a third dose.

Dealing with disruptions

No matter how severe the case, a positive COVID-19 test can cause a person to be sidelined from everyday life. The CDC recommends a minimum 10-day quarantine after a positive test. Many workplaces and schools enforce this not only for the vaccinated individual but also for their close contacts and family members.

Del Rio said enforcing these intense quarantines doesn’t necessarily make sense at this point, and other mitigation and protection measures can help allow a return to normal life. For example, if a kid in a classroom contracts COVID-19, but every child in the classroom is masked and all the adults in that child’s life are vaccinated, there’s no cause for alarm.

COVID-19 vaccines were never expected to zap the virus completely — from the outset, public health officials said the goal was to slow the spread and make the virus less deadly. And while vaccinated individuals who contract COVID-19 can still spread the virus to others, it’s much less common. A person with a breakthrough infection has a much lighter viral load than an unvaccinated person with COVID-19.

The widespread use of rapid antigen tests is one way to allow life to return to normal, Adalja suggested. Although seen as less reliable than PCR tests, an antigen test can determine whether a person with a breakthrough case has enough virus in their body to spread to others.

Last week, the White House announced a major testing initiative to use the Defense Production Act to increase the availability of over-the-counter, rapid COVID-19 tests. President Joe Biden also directed Walmart, Kroger and Amazon to sell those tests at cost for the next three months, as more and more Americans will likely find themselves needing a quick at-home test amid high community spread.

“Five years from now, people are gonna say, ‘Oh, that person’s out, he’s got COVID. Whatever, it’s not that big of a deal.’ But right now, we’ve got a risk tolerance level that’s very low,” Adalja said.

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