Current Boosters—Not Delta-Targeted Ones—Called Best Bet for Now

Tailoring Covid-19 booster shots to work against variants such as delta would offer less overall protection from the virus than using an additional dose of the original shot, an NIH immunologist whose work was critical to the vaccine developed by Moderna Inc., said.

Studies have indicated that boosting with the original vaccine increases the response and neutralizing activity against all the variants, Barney S. Graham, a top immunologist at the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, said Thursday at the American Society of Tropical Medicine and Hygiene’s annual meeting.

“Boosting with one variant versus another may not reach all variants as well as the original ancestral variant,” he said. “For instance, if you’re immunized with the beta variant, it wouldn’t do as well against delta as the ancestral would.”

Graham’s comments come as the Food and Drug Administration is expected this week to authorize Pfizer Inc. boosters for all U.S. adults. Pfizer and BioNTech are working on a delta-specific booster as questions swirl over why the third shots currently available are the same as the original vaccine, which was designed against the original strain of SARS-Cov-2, the virus that causes Covid-19.

Graham recently stepped down as deputy director of the NIAID’s Vaccine Research Center but is still active within the institute. His team, which included Kizzmekia S. Corbett, came up with a vaccine based on the genetic sequence of SARS-Cov-2, which Moderna ultimately developed.

An advisory panel for the Centers for Disease Control and Prevention is scheduled to meet on Friday to consider recommendations on letting all U.S. adults access Pfizer booster shots. Moderna filed the same request on Wednesday.

Ancestral Strain

Viruses mutate all the time; the variants like delta are changes the virus makes so it can better transmit and grow in human tissue. At some point vaccine companies may have to make products to reach the current circulating strains. But that wouldn’t be necessary until there’s more of a linear evolution like the influenza virus, which “really keeps continuing to drift away from the center,” Graham said.

“But right now, I think the ancestral variants are boosting well enough to cover all the variants that I know.”

Graham also expects to see more mixing-and matching, in which the booster comes from a different vaccine than the primary series, such as an initial Johnson & Johnson adenovirus-based vaccine followed by a Moderna or Pfizer booster.

“So we’ve seen that adenovirus vector priming with an mRNA boost is very attractive, I think we’ll also see eventually that boosting with a protein is going to be a remarkably good way of boosting people in the future,” he said.

One of the companies making a protein-based vaccine is Novavax Inc. , whose CEO said earlier this month their Covid-19 vaccine could be a good booster option for people who have received other shots.

“As time goes on, it’s not just mRNA. A lot of other modalities may be better fit for different points of this epidemic,” Graham said. “It may be that in three years, the protein-based vaccines will be shown the kind of potency and durability and low-cost manufacturing that may be more useful.”