How Does COVID-19 'Break Through' in Vaccinated People?

Hundreds of festival-goers, most not wearing masks, groove to the music during the HARD Summer music festival on July 31, 2021, in San Bernardino, California. Despite the increase in the delta variant, the promoters allowed the festival to continue. Gina Ferazzi / Los Angeles Times via Getty Images

When the COVID-19 vaccine became available, Perry Knight of Fort Lauderdale, Florida, got in line as soon as he was eligible. He'd already done battle with the virus and wasn't interested in going there again. "I first tested positive in August of 2020, and spent two nights in the hospital because I was having a hell of a time just catching my breath. It had to be up there as one of the worst experiences of my life," says Knight in an email. "It's like being underwater and about to come up for fresh air, and halfway through drawing that fresh air, a tightness interrupts it."

Knight got both doses of the Pfizer vaccine in May 2021. Despite that, he wasn't too surprised when he tested positive in July. "I was more of having a feeling like, 'Wow, I should just play the lottery, because this luck is incredible' if you know what I mean," recalls the cycling enthusiast and lead editor at Wheeligreat. "I was mentally preparing to go back into the hospital for another horrible couple days." Fortunately, his second go-round with COVID-19 was nothing like the first. His symptoms were mild and short-lived, an experience that has only strengthened his appreciation of the vaccine.

"After seeing firsthand my experience with COVID with and without the vaccine, it's given me enough faith in the medical system that vaccinations are doing their part to protect us," he says. "It's not a shield 100 percent preventing the virus from getting to us, but it's a relentless warrior who really keeps the worst of it at bay."

Still, it really upsets a lot of people that COVID-19 is possible, post-vaccine. How does that even happen? "When a person gets COVID-19 even after being fully vaccinated, this is known as a breakthrough infection since it breaks through the developed immune response," explains Dr. Sri Banerjee, faculty member in Walden University's Ph.D. in Public Health program via email.

This type of COVID "breakthrough infection" is not unusual. Indeed, it's actually to be expected, given the virus's recent mutation. "With the delta variant it certainly is more common," says Dr. Aaron Glatt, representative for the Infectious Diseases Society of America (IDSA) and chair of medicine at Mount Sinai South Nassau in Oceanside, New York. "These variants have higher transmissibility than the earlier strains. They also have higher viral loads, so they're more transmissible even to people who are vaccinated, so this is a concern."

Breakthrough infections are nothing new. In fact, the medical community sees them every single year with regard to influenza. However, most people believe that vaccines provide complete and total protection. "Being vaccinated doesn't mean you won't get the infection; it only increases your capability of fighting the virus effectively," emails Dr. Hira Shaheen, who treated COVID-19 patients in Pakistan and is a consultant for home improvement site Sensible Digs. "Vaccines are designed to prevent complications and death, and their impact on transmission is less pronounced (at least until herd immunity develops)."

How Effective Are COVID-19 Vaccines?

For their part, pharmaceutical companies have been straightforward from the get-go about vaccine efficacy. Both Pfizer and Moderna reported efficacy rates of 90 to 95 percent for the original strain. Pfizer's drops to 88 percent when faced with the newer, more contagious delta mutation. Moderna is believed about the same efficacy against delta as Pfizer, since both are mRNA vaccines.

Breakthrough infections are typically so mild, in fact, that the Centers for Disease Control and Prevention (CDC) stopped tracking them starting May 1, 2021, unless such cases result in hospitalization or death. So, for CDC tracking purposes, a mild case of COVID-19 after vaccination is not considered a "breakthrough infection."

"Nationally, 46 U.S. states and territories voluntarily reported 10,262 breakthrough infections to the U.S. Centers for Disease Control and Prevention (CDC) between January 1 and April 30, 2021. By comparison, there were 11.8 million COVID-19 diagnoses in total during the same period," says Banerjee. "Through July 19, 2021, there were 5,914 patients with COVID-19 vaccine breakthrough infections who were hospitalized or died in the U.S., out of more than 159 million people fully vaccinated nationwide.

"With that in mind, it is difficult to determine the rarity of breakthrough infections as there is not any concrete, consistent data. Certain factors complicate how breakthrough infections are counted. The main problem is tracking the prevalence, as many do not experience symptoms even if they contract a breakthrough infection. Another challenge is to determine which individuals with COVID-19 are in a long-COVID phase rather than a potential reinfection," he adds.

While it may be difficult to determine just how many people experience any type of COVID-19-related symptoms after vaccination, we can see that the numbers of people who get them are small. Just as important, if they do get COVID-19, the symptoms will be much milder than if they had been unvaccinated. One study found that fully vaccinated people accounted for only 1.2 percent of COVID-19 cases.

Do You Really Need to Mask Up If You're Vaccinated?

On Aug. 2, 2021, the White House COVID data director announced that at least 70 percent of adults in America have gotten at least one shot of the vaccine (the two most common vaccinations require two jabs weeks apart to achieve full immunity). This was good news, as a full vaccination rate of 70 to 90 percent is needed for herd immunity. Until that's achieved, breakthrough infections are likely to continue with a vengeance. As of Aug. 1, 2021, only 49.7 percent of eligible people in the United States were fully vaccinated against COVID-19, and that number varies widely by state.

The CDC had dropped its masking guideline for vaccinated people in May. In late July, it reversed itself and said vaccinated people in areas with "substantial or high transmission" should wear masks indoors. New data had shown that vaccinated people who had the delta variant could transmit the virus as easily as unvaccinated people.

Until herd immunity is reached, breakthrough infections shouldn't keep people from getting vaccinated against COVID-19. Indeed, medical experts urge more people to get vaccinated to keep COVID at bay. "Unfortunately, it's likely that the remaining phases of the pandemic will predominantly impact the unvaccinated segment of the population," says epidemiologist, Dr. Matt Weissenbach, with Wolters Kluwer, Health. "Vaccination remains the single most important choice to protect yourself, your loved ones and your community against COVID-19."