COVID-19 infections and hospitalizations in the U.S. are on the rise as the highly contagious delta variant spreads, driven by the least vaccinated parts of the country.
And while no vaccine is perfect, meaning fully vaccinated people occasionally will get infected, those so-called breakthrough cases are rare and usually are mild. They are also expected.
The advice from medical experts is clear: vaccines remain the most effective way to protect oneself from the worst effects of COVID-19 and bring an end to the pandemic. And if you are vaccinated, how worried should you be about breakthrough cases? Your questions answered:
U.S. & World
What is a breakthrough COVID-19 case?
Vaccine "breakthrough cases" are instances in which a person received a positive COVID-19 test result at least 14 days after the final dose of any COVID-19 vaccine series. This definition includes everything from asymptomatic infections to cases that result in hospitalization and death.
Breakthrough cases are sometimes identified through mandatory testing before surgery or to go back to work, not because vaccinated people are showing symptoms. In fact, at least two fully vaccinated Olympians on Team USA's roster have tested positive for COVID-19 and neither of the two athletes reported feeling any symptoms.
State and federal health officials are tracking “breakthrough cases” to help understand transmission among vaccinated people and whether the vaccines might not work as well against certain strains of the virus.
Current data suggests that the three coronavirus vaccines authorized for emergency use in the U.S. offer protection against most SARS-CoV-2 variants circulating in the U.S. Vaccines from Pfizer and Moderna are about 90% effective against infection once two weeks after the last dose have passed. The one-dose Johnson & Johnson vaccine is about 72% effective against moderate to severe disease, according to U.S. trials.
How many fully vaccinated people have gotten COVID-19 in the U.S.?
The number of breakthrough cases is largely unknown after the CDC shifted to tracking only the breakthrough infections that resulted in hospitalization or death starting on May 1. But from January to April 30, the CDC reported over 10,000 breakthrough cases in 46 states and territories.
An NBC News analysis of available government data found that in 27 states that continue tracking all breakthrough infections, more than 65,000 cases have been reported.
As of July 12, the CDC reported 5,492 cases of breakthrough COVID-19 cases that led to hospitalization or death among the over 159 million fully vaccinated people in the U.S. That translates to about .0003% breakthrough rate for severe disease. And 75% percent of those patients were over the age of 65.
More than 97% of people who are entering hospitals with symptomatic COVID-19 infections are unvaccinated, according to the CDC.
“The main takeaway is that COVID-19 vaccines are highly effective and cases of infection after a person is fully vaccinated are very rare,” Dr. Deidre Gifford, Connecticut's acting public health commissioner, said in a statement.
Are some people more at risk for severe breakthrough infections?
Vaccines have significantly contributed to the decrease in cases across much of the United States over the past six months. While the spread of more transmissible variants like Delta may cause increased breakthrough cases, available data suggests the authorized COVID-19 vaccines offer protection against most SARS-CoV-2 strains circulating in the U.S..
Still, some populations are at greater risk for severe breakthrough cases, such as immunocompromised patients or people with underlying medical conditions.
An NBC News survey of health officials nationwide found that fully vaccinated individuals who got very sick or died tended to be older 65 or have weakened immune systems.
"Throughout the pandemic, people who died of Covid-19 were most likely to be older, and that continues to be true with breakthrough cases," a spokesperson for the Massachusetts Department of Public Health told NBC.
In Washington, one of several states that tracks all breakthrough infections, more than 50% of all breakthrough cases occurred in people over the age of 50. Of those who died of a COVID-19 related illness, 69% had one or more underlying conditions and more than half were "known to be associated with a long-term care facility."
The data mirrors trends outside the U.S. A study in Israel of 152 breakthrough infections leading to hospitalization found only 6% had no underlying health conditions. The remaining patients had conditions ranging from hypertension and diabetes to dementia and cancer.
The CDC says it's also possible that a person could be infected just before or just after vaccination and still get sick. It typically takes about 2 weeks for the body to build protection after vaccination, so someone could get sick if the vaccine has not had enough time to provide protection.
Symptoms of breakthrough COVID cases
When fully vaccinated individuals do have symptomatic SARS-CoV-2 infections, their cases are usually mild.
The five most common symptoms of COVID-19 in fully vaccinated people are headache, runny nose, sneezing, sore throat and loss of smell, according to research from Tim Spector, a London-based epidemiologist.
Should I be worried about breakthrough cases?
The existence of breakthrough cases is not inherently cause for alarm. According to the CDC, fully vaccinated people are much less likely to be hospitalized or die than unvaccinated individuals with similar risk factors. And for those who do develop symptoms post-vaccination, their symptoms should be less severe with vaccination than without it.
Most COVID-19 cases are occurring among the unvaccinated. As CDC Director Dr. Rochelle Walensky said Friday, "this is becoming a pandemic of the unvaccinated.” At a White House briefing, Walensky said cases have risen by 70% over the last week. Hospital admissions are up 36% and deaths by 26% — nearly all of them among the unvaccinated.
The longer the pandemic rages, experts say the more likely it is new variants with greater strength against the current vaccines will emerge and increase the likelihood of more breakthrough cases.