Vaccines’ protection against virus infection is waning, CDC studies suggest

The Centers for Disease Control and Prevention released three studies Wednesday that federal officials said provided evidence that booster shots of the Pfizer-BioNTech and Moderna coronavirus vaccines would be needed by all Americans in the coming months.

But some experts said the new research did not support the decision to recommend booster shots for all Americans.

Taken together, the studies show that although the vaccines remain highly effective against hospitalisations, the bulwark they provide against infection with the virus has weakened in the past few months.

It is unclear whether the decline in protection against infection is the result of waning immunity, a drop in precautions like wearing masks, or the rise of the highly contagious delta variant — or a combination of all three.

“We are concerned that this pattern of decline we are seeing will continue in the months ahead, which could lead to reduced protection against severe disease, hospitalisation and death,” Dr. Vivek Murthy, the surgeon general, said at a White House news briefing Wednesday.

Citing the data, federal health officials outlined a plan for Americans who received the two vaccines to get booster shots eight months after receiving their second doses, starting Sept. 20.

Some scientists were deeply sceptical of the new plan.

“These data support giving additional doses of vaccine to highly immunocompromised persons and nursing home residents, not to the general public,” said Dr. Celine Gounder, an infectious disease specialist at Bellevue Hospital Center and a former adviser on the pandemic to the administration.

Boosters would only be warranted if the vaccines were failing to prevent people from ending up hospitalised with COVID-19, she said.

“Feeling sick like a dog and laid up in bed, but not in the hospital with severe COVID, is not a good enough reason,” Gounder said. “We’ll be better protected by vaccinating the unvaccinated here and around the world.”

It is unclear whether a third dose would help people who did not produce a robust response to the first two doses, said Bill Hanage, a public health researcher at the Harvard T.H. Chan School of Public Health.

The recommendation for boosters may also end up undermining confidence in vaccines, he warned: “A third shot will add to scepticism among people yet to receive one dose that the vaccines help them.”

Together, the new studies indicate overall that vaccines have an effectiveness of roughly 55% against infections, 80% against symptomatic infection and 90% or higher against hospitalisation, noted Ellie Murray, a public health researcher at Boston University.

“Those numbers are actually very good,” Murray said. “The only group that these data would suggest boosters for, to me, is the immunocompromised.”

The drop in protection against infection could be the result of increased exposure to a highly contagious variant during a period of unfettered social interactions, she added. “This seems to me like a real possibility, since many early vaccinated were motivated by a desire to see friends and family and get back to normal.”

Murray said boosters would undoubtedly boost immunity in an individual, but the benefit may be minimal — and obtained just as easily by wearing a mask or avoiding indoor dining and crowded bars.

The administration’s emphasis on vaccines has undermined the importance of building other precautions into people’s lives in ways that are comfortable and sustainable, and on building capacity for testing, she and other experts said.

“This is part of why I think the administration’s focus on vaccines is so damaging to morale,” she added. “We probably won’t be going back to normal anytime soon.”

Before people can begin to receive boosters, the Food and Drug Administration must first authorise a third dose of the mRNA vaccines made by Pfizer-BioNTech and Moderna, and an advisory committee of the CDC must review the evidence and make recommendations.

One of the new CDC studies analysed the effectiveness of vaccines among residents of nearly 4,000 nursing homes from March 1 to May 9, before the delta variant’s emergence, and nearly 15,000 nursing homes from June 21 to Aug. 1, when the variant dominated new infections in the country.

The vaccines’ effectiveness at preventing infections dropped from about 75% to 53% between those dates, the study found. It did not evaluate the vaccines’ protection against severe illness.

Nursing homes were required to report the number of immunised residents only after June 6, which “makes comparisons over time very challenging,” Murray said. “It’s fully possible that the vaccine effectiveness reported here hasn’t actually declined over time.”

The decline in effectiveness also could have resulted from the spread of the delta variant, Gounder said.

“It makes sense to give an extra dose of vaccine to vaccinated nursing home residents, but what will have an even bigger impact on protecting those nursing home residents is to vaccinate their caregivers,” she said. Many heath aides in long-term care facilities remain unvaccinated.

A second study evaluated data from New York state from May 3 to July 25, when the delta variant grew to represent more than 80% of new cases. The effectiveness of vaccines in preventing cases in adults declined from 91.7% to 79.8% during that time, the study found. But the vaccines remained just as effective at preventing hospitalisations.

During those weeks, New York recorded 9,675 breakthrough infections — roughly 20% of total cases in the state — and 1,271 hospitalisations in vaccinated people, which accounted for 15% of all COVID-19 hospitalisations.

Although fully immunised people of all ages got infected with the virus, vaccine effectiveness showed the sharpest drop, from 90.6% to 74.6%, in people ages 18 through 49 years — who are often the least likely to take precautions and the most likely to socialise.

Data from Israel has suggested that immunity against infection has waned in vaccinated adults who are 65 or older. But in the New York data, the effectiveness of the vaccines in that group barely budged.

Adults age 65 or older were more likely to be hospitalised than other age groups, regardless of vaccination status. But the vaccines did not show a decline in effectiveness against hospitalisations in any of the age groups.

The third study from the CDC found that the vaccines showed 90% effectiveness against hospitalisations in the country, “which is excellent,” Gounder noted.

The vaccines were less protective against hospitalisation in immunocompromised people. “But not all immunocompromised persons will respond to an additional dose of vaccine,” Gounder noted.

To protect these vulnerable individuals, everyone around them should be vaccinated and should continue to wear masks, she added.

The vaccines may appear to be less effective than they did in the clinical trials because the trials were conducted before the emergence of the highly contagious delta variant. The vaccines can also seem to lose effectiveness as more unvaccinated people become infected with the virus and gain natural immunity.

If preventing infection is the goal, it would be wiser to offer a booster of a nasal spray vaccine, which is better at inducing immunity in the nose and throat, where the virus enters, Gounder said.

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