NEW ORLEANS — More than 120 fully vaccinated people in Louisiana have tested positive for COVID-19 more than two weeks after their last dose of the vaccine, according to officials with the Louisiana Department of Health.
That there is a small number of so-called “breakthrough cases” is no surprise, officials say. “I think it’s in line with what you would expect from the trials,” said Dr. Joe Kanter, Louisiana’s state health officer.
A recent study from the Centers for Disease Control and Prevention showed that 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.
State 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. And though breakthrough cases are rare — 126 cases among 568,968 fully vaccinated people works out to about .02%, or about 1 case for every 4,500 vaccinated people to date — they are a reminder that people who have had their shots should take precautions like masking and distancing in public.
“The vaccine is not a blank check to do whatever you want,” said Dr. Julio Figueroa, head of infectious diseases at LSU Health New Orleans.
Breakthrough cases are sometimes identified through mandatory testing before surgery or to go back to work, not because vaccinated people are showing symptoms.
As more people get vaccinated, the rate of new breakthrough cases should decrease, said Figueroa. That’s in part because research is showing vaccinated people who get COVID, whether they are symptomatic or not, carry a lower viral load and transmit the disease less.
“What we want to do is drop the entire population’s viral shedding so that we have less and less transmission,” said Figueroa.
Other states and researchers are also tracking breakthrough cases, with results that also suggest it’s a rare occurrence. One study from the University of Texas Southwestern Medical Center in Dallas found that only four out of 8,121 employees who were at least two weeks past their final dose were infected — about .04%. Another found that just seven of 14,990 employees at two California hospitals later were infected, a similar rate.
In Washington state, only about 100 of 1.2 million fully vaccinated people have tested positive for the coronavirus. Most experienced mild symptoms, in line with results from clinical trials suggesting the vaccines lessen the severity of the disease.
But eight of those breakthrough cases resulted in hospitalization, and two people who died were being investigated as breakthrough cases, according to the Washington State Department of Health. Both were older than 80 with health issues.
Louisiana officials were not able to share data on disease severity in breakthrough cases or say which vaccine individuals received.
The CDC recommends vaccinated people continue to wear masks in public and around unvaccinated people. Experts said this guidance may loosen as more people get the shots, but widespread vaccination is necessary to provide a blanket of protection for vulnerable people.
“You want to vaccinate the population as much as possible so you get that herd immunity,” said Figueroa. “Those susceptible people, even if they’ve gotten vaccinated, will be protected.”