Comparing neutralizing antibody titers in blood samples from 21 people who received the booster targeting the omicron BA.4 and BA.5 variants with those of 19 people who got four shots of the original vaccines, the study reportedly showed no significant difference three to five weeks after the last immunization.

On the surface, the new results appear to contradict early data from a Phase 2/3 clinical trial communicated by Pfizer/BioNTech on Oct. 13. In this, the American/German partners said their new booster, designed as a fourth dose, “is anticipated to provide better protection.” The statement was based on data collected only seven days after immunization.

In early October, Moderna published data from a clinical trial with its other bivalent booster that is tailored to the original omicron strain (BA.1), no longer widely circulating. This shot, the vaccine maker said, produced higher levels of antibodies produced compared to four shots of its original vaccine.

“So far we don’t see the benefit” of the bivalent shots over the old ones, the university study’s senior author David Ho, a virologist who heads the Aaron Diamond AIDS Research Center at Columbia University, told the Bloomberg new agency. However, he added that “a clear difference between the boosters could emerge over longer periods of time.”

The lackluster results for bivalent boosters, Ho explained, could be due to imprinting, which means that the immune system most strongly remembers the first version of a virus it encounters. After it mutates, the response to a vaccine, even one targeting newer strains, may still be tilted toward fighting the original pathogen.

Author: Dede Williams, Freelance Journalist