CDC data from this spring show those vaccinated and boosted were twice as likely to get COVID as those vaccinated but not boosted. Newsday TV's Steve Langford reports.  Credit: Kendall Rodriguez

COVID-19 boosters are designed to pump up the immune system as protection from the initial shots wanes, but federal data released Friday shows a surprising trend: For months, people with booster shots have been more likely than non-boosted vaccinated people to get infected with the coronavirus.

Medical experts said boosters can only do so much to battle omicron subvariants that are more contagious than previous virus strains, especially as immunity from the boosters declines over months and boosted people venture into increasingly riskier settings. Experts also said many boosted people may have been more cautious in the past, so they may have avoided getting the virus and don’t have the added immunity from previous infection.

“Part of it is just behavior and risk,” said Dr. Steven Carsons, director of the Vaccine Center at NYU Langone Hospital-Long Island in Mineola. “People who are boosted feel that they’re really protected based on the older data.”

They may have a false sense of security, not realizing that omicron, which became dominant in December, is better able than previous variants to evade the protection of the vaccines, including boosters, and infect vaccinated people, he said.

WHAT TO KNOW

  • Even though COVID-19 boosters are intended to increase protection against COVID-19, federal data shows that people with boosters are now more likely to test positive than vaccinated people without boosters.
  • Experts say the waning protection from boosters — some people received their first boosters nine months ago — and increased risks that boosted people may be taking, along with the lack of a previous infection to provide additional immunity, may be among the reasons.
  • Boosted people are still less likely to be hospitalized for or die from COVID-19 than a non-boosted vaccinated person, and much less likely than unvaccinated people. But even those gaps have not been as large in recent months.

“I struggle with myself,” Carsons said, regarding how much risk to take. He spoke by phone from home, where he was recovering from COVID-19 after getting infected for what he believed was the first time.

Carsons received his second booster on April 2, and in part because of that, “I was doing things the last couple of weeks I wouldn’t have done” previously, including dining indoors at restaurants.

“Part of it is just behavior and risk,” said Dr....

“Part of it is just behavior and risk,” said Dr. Steven Carsons, director of the Vaccine Center at NYU Langone Hospital-Long Island in Mineola. Credit: NYU Langone Health

People 50 or older, along with those 12 and older who are moderately or severely immunocompromised, are eligible for a second booster shot, as are adults who received a Johnson & Johnson vaccine plus one Johnson & Johnson booster.

Dr. Bruce Farber, chief of public health and epidemiology for Northwell Health, cautioned that the shift in infections shouldn’t discourage people from getting boosters.

“There is no suggestion or data that the booster increases your risk of getting COVID,” he said.

Boosted people still are least likely to end up in the hospital or die of COVID-19, Centers for Disease Control and Prevention data show. Plus, unvaccinated Americans remain at far greater risk of dying or getting severely ill from the disease than vaccinated people, and they are at higher risk of getting infected, research shows.

The CDC, in an email response to Newsday about boosters, wrote: "In well-controlled vaccine effectiveness studies, booster doses have been shown to offer higher protection against infection, hospitalization, and death, than a primary series alone, including during the omicron period."

Dr. Wafaa El-Sadr, a professor of epidemiology and medicine at the Mailman School of Public Health at Columbia University, said people choosing to get boosted "are in all likelihood quite different from the people who are not." That includes, for example, health care workers and people who are regularly in crowded environments, she said.

“It’s possible the people seeking boosters are at higher risk of COVID, and are more likely to be in situations where you could get the virus, and that’s the reason they want to be boosted,” she said.

Boosted people also may be more likely to seek tests in hospitals, health centers and other sites outside the home, and that could push up their infection numbers in official statistics, El-Sadr said. 

Home tests typically aren’t reported to authorities, meaning they’re not counted in government infection data, leading to a huge undercount and misleading statistics, including on differences between boosted people and others, she said.

The current vaccines, including the boosters, were developed to fight earlier strains of COVID-19. But the virus has mutated over time, which is why vaccines are less effective against infection today than in the past. Researchers at NYU Langone Hospital-Long Island and other sites nationwide are working to create vaccines that would be more effective against future variants.

Rates changed as omicron took hold

Boosters were first authorized in September, and for months, people with boosters were less likely to get infected than non-boosted vaccinated people, and far less likely to get infected than unvaccinated people, CDC data shows.

For example, in the week beginning Nov. 28, the COVID-19 case rate was about 43 per 100,000 for boosted people ages 12 and older, compared with 153 per 100,000 for non-boosted vaccinated people, and 571 per 100,000 for unvaccinated people.

The numbers started narrowing in mid-December, when the omicron variant began dominating and after nearly three months had passed from when the first groups of people received their boosters.

In the week starting Feb. 13, the infection rate for boosted people surpassed that of people with only initial shots.

In CDC data released Friday, from the week beginning May 15, the rate for boosted people was 247 per 100,000, compared with 121 per 100,000 for non-boosted vaccinated people and 422 per 100,000 for unvaccinated people.

The CDC on Friday also released data on people 50 and older with two boosters. They had a rate for the week starting May 15 of 162 per 100,000, versus 201 per 100,000 for those with one booster, 128 per 100,000 for vaccinated people with no booster, and 615 per 100,000 for the unvaccinated.

New York State does not break out infection or hospitalization data of vaccinated people by booster status.

Data reported by New York City, which goes through the week ending June 4, shows that people there with boosters are more likely to test positive than vaccinated people without them.

Dr. David Hirschwerk, an infectious disease expert and medical director of North Shore University Hospital in Manhasset, noted some people received their first booster nine months ago, and many eligible for a second booster haven’t gotten one.

“There certainly is some degree of waning immunity,” he said.

During the major winter omicron surge, many non-boosted people contracted the virus, “and the infection they experienced may have provided some subsequent protection from reinfection,” he said.

Hirschwerk said decisions about what risks to take are "personal."

David Hirschwerk, an infectious disease expert and medical director of...

David Hirschwerk, an infectious disease expert and medical director of North Shore University Hospital in Manhasset, said many who are eligible for a second booster haven’t gotten one. Credit: Northwell Health

“When the rates are high and you’re in large gatherings in indoor spaces, it’s reasonable for people to want to wear masks, especially if they’re at risk for severe illness because of their age or underlying conditions," he said. "But at the end of the day, it’s a judgment call that people make for themselves.”

Hirschwerk characterized current COVID-19 rates as “relatively high.” But, he said, “Once the rates get down to be very low, then the need to take these extra steps, including mask-wearing in indoor environments, starts to really go down as well.”

An Israeli study released in April found that additional protection from the second booster for those 60 and older was strong for the first four weeks, but fell significantly afterward. The study found continued strong protection against severe illness six weeks later.

Boosted, non-boosted gaps narrow 

Hirschwerk said that's where the focus should be: on how boosters decrease the chances of severe illness or death.

Yet even the gap between those rates had narrowed during the omicron surge, although actual numbers declined after the massive winter omicron spike. 

In the late fall and early winter, the death rate for boosted people was typically about three to five times lower than that of vaccinated people without boosters, and up to 70 times less than that of unvaccinated people, CDC data shows.

In CDC data released Friday from the week beginning April 24, the latest available, the COVID-19 death rate for boosted people 12 and older was 14% lower than that of non-boosted vaccinated people: 0.12 per 100,000 for boosted people, compared with 0.14 for those vaccinated without a booster. It was nearly seven times lower than the rate for unvaccinated people, which was 0.79.

But people with two booster shots had by far the lowest death rates, data from that week shows: 0.03 for twice-boosted people 50 and older, compared with 0.29 for people of that age with one booster, 0.4 for non-boosted vaccinated people of that age, and 71 times lower than the 2.14 rate for the unvaccinated of that age.

The hospitalization gap also narrowed. In mid-November, for example, boosted people were more than six times less likely to be hospitalized than non-boosted vaccinated people, and 56 times less likely to be hospitalized than unvaccinated people.

By the week ending March 19, boosted people were about 45% less likely to be hospitalized than non-boosted vaccinated people, and about five times less likely than unvaccinated people.

CDC hospitalization data released Friday, which was through the end of April, did not compare boosted and non-boosted vaccinated people but showed that boosted people were nearly four times less likely to be hospitalized than unvaccinated people.

Carsons said one reason for the narrowing gaps could be that many severely immunocompromised people — such as those on chemotherapy, transplant recipients and people with autoimmune diseases — are boosted, but because of their conditions, many don’t produce antibodies, even after one or two boosters. That puts them at higher risk for hospitalization and death. Some are unaware of that and may believe they are more protected than they really are, he said.

Another reason is the large number of boosted people in recent months counted as COVID-19 hospitalizations who entered the hospital for another reason — like a broken leg or a heart condition — and later tested positive, Carsons said.

“The bottom line is obviously that the vaccines and medications have made a tremendous difference in avoiding hospitalization and death and bad outcomes overall,” he said.