: COVID-19 vaccine booster shots are more complicated than they appear. Here’s why.

Not everyone agrees that COVID-19 booster shots are necessary for all vaccinated Americans, and that discord may slow down plans to roll out extra doses of the mRNA vaccines later this month and change who is eligible for them.

Dr. Sara Oliver, a Centers for Disease Control and Prevention official who leads the COVID-19 vaccines work group, on Monday said the “priority for booster dose policy should be the prevention of severe disease in at-risk populations,” citing nursing-home residents and frontline healthcare workers as examples. 

The presentation was part of a meeting of the CDC’s Advisory Committee on Immunization Practices, or ACIP, a group of independent public health experts who make recommendations about vaccines to the CDC following authorization or approval from the Food and Drug Administration. 

White House officials, including President Joe Biden, last month said that Americans who were vaccinated with the vaccines from BioNTech SE

and Pfizer Inc.

or Moderna Inc.

can get a booster dose starting Sept. 20, as long it has been eight months since the person has been fully vaccinated, the FDA authorizes or approves the booster, and the CDC gives its blessing. They said the first boosters will likely go to groups of people who are at higher risk of severe disease. 

(The White House also said that people who got Johnson & Johnson’s

single-shot vaccine will likely need a second dose, though no further details have been shared at this time.)

That said, U.S. regulators have yet to OK a booster dose for the general public, and that has become a point of contention for some public health experts.

The Biden administration’s announcement “led everyone — it led physicians, it led the public — to believe that they had access to information about these vaccines and the need for boosters that had not yet been publicly released,” Dr. Sandra Adamson Fryhofer, an adjunct associate professor of medicine at Emory University School of Medicine, said Monday. “To me, that opened the door to a lot of confusion.”

Fryhofer serves as a liaison to ACIP for the American Medical Association.

Federal health officials have said they are concerned that the vaccines will soon be less effective at protecting people against severe disease, hospitalization and death, and that is their rationale for booster shots.

Asked about the ACIP’s booster discussion on Tuesday, CDC director Dr. Rochelle Walensky responded that the committee had only evaluated U.S. data so far.

“It is our own data as well as international data that has led us to be concerned that the waning we’re seeing for infection will soon lead to waning that we would see for hospitalization and severe disease and death,” she said.

However, infectious-disease physicians have previously told MarketWatch that clinical decisions for COVID-19 booster shots should be based on data that’s available, not what’s projected to happen. 

What’s changed in the COVID-19 booster discussion

The national discourse around boosters has intensified over the last two months, driven by public promotion from Pfizer and Moderna, the Biden administration’s sudden support, and widespread utilization of extra doses in Israel, which is being closely watched by scientists to see how virus behaves in the highly vaccinated country. 

At the same time, cases have steadily increased in the U.S. since early July, as immunity has waned over time and the rapid spread of the more infectious delta variant has led to an increase in infections among the unvaccinated as well as the vaccinated. 

This was reiterated by Oliver at Monday’s meeting.

“All [COVID-19] vaccines remain effective in preventing hospitalization and severe disease, but they may be less effective in preventing infection or mild illness recently,” she said. “These reasons for lower effectiveness likely include both waning over time and the delta variant.”

However, most of the soaring numbers of hospitalizations and deaths we are seeing right now are occurring in unvaccinated Americans. 

“The data to date doesn’t show a remarkable reduction in the effectiveness of vaccines in terms of preventing hospitalizations and deaths,” Dr. Beth Bell, a clinical professor at the University of Washington’s School of Public Health and an ACIP member, said Monday. “The most important thing that we can do with respect to vaccines is to continue to work as hard as we possibly can to encourage more people to get the primary series.”

What exactly is a COVID-19 booster shot?

This is where things get complicated.

The CDC does not refer to an extra dose administered to the immunocompromised as a booster shot. Instead, that is considered a third — or extra — dose because many of those people never mounted an immune response at all to initial vaccination, according to Oliver. (The only Americans who are currently eligible for an extra dose of the BioNTech/Pfizer vaccine — now marketed as Comirnaty — or the Moderna vaccine are some teens and adults with compromised immune systems, an authorization that was granted in August.)

The agency defines a booster dose as one that “boosts” immunity from a vaccine’s “primary series” that has waned over time.

There are also different kinds of boosters. A homologous booster uses the same vaccine, while a heterologous booster uses a different vaccine for the booster from that used in the primary series.

Several “mix and match” clinical trials are already under way around the world, including one conducted by the National Institutes of Health that is testing a Moderna booster in people who received any of the three authorized or approved COVID-19 vaccines. 

In addition, drug makers are testing different doses of the vaccines in booster trials.

There is one more one idea to consider: that perhaps the two-dose COVID-19 vaccines will actually become three-dose vaccines. (Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, told MarketWatch in August that this seems to be the White House’s plan. His view is that officials there are saying, ” ‘Let’s not wait for an erosion against severe illness. We’ll just offer a booster now, with the assumption being with that this will be a three-dose vaccine.’ “)

Other vaccines including the human papillomavirus (HPV) and hepatitis B shots require three doses, spaced out over a year or so. For example, the third dose of the hepatitis B vaccine can be administered up to 18 months after the first dose.

“In a pandemic setting, it can be important to achieve high protection early with a second dose given at a shorter interval, however it may mean that a later dose for this boost effect is needed as well,” Oliver said. “This doesn’t necessarily mean that an annual booster dose would be needed.”

What comes next

BioNTech and Pfizer said last week that they had submitted data for a Comirnaty booster shot to the FDA. That data examined antibody levels in adults who got a third dose between four and eight months after initial vaccination.

Moderna said Wednesday that it had submitted its booster data to the FDA.

J&J has said that booster doses can increase antibody levels among people immunized with its vaccines, though the company has not submitted that data to U.S. regulators at this time. 

The ACIP is expected to meet again in mid-September, or if and when the FDA authorizes or approves a third dose of one of the vaccines, to discuss how COVID-19 booster shots should be administered to the public. Monday’s meeting focused on setting out a framework for booster shots in the U.S.

BioNTech/Pfizer, J&J and Moderna will be asked to present clinical data for booster doses at coming meetings. 

“We read this meeting timing and the additional dose (‘booster’) discussion as an indication that uptick in third doses may not come as rapidly as investors have been expecting,” SVB Leerink analyst Daina Graybosch told investors on Tuesday. 

Jefferies analysts took a much more narrow view of the meeting, telling investors that they think the committee is leaning toward only recommending booster doses for high-risk populations like healthcare workers and the elderly. 

“The ACIP still appears to be hesitant on whether [additional] doses are needed despite waning antibodies and increasing infections,” they wrote. 

This post was originally published on Market Watch

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