More COVID-19 Vaccine Updates: How Effective Are New Boosters?

Volume 23, Issue 2

This winter has been relatively calm from a COVID-19 standpoint. While cases and hospitalizations are up, there hasn’t been any surge resembling last year’s with the original Omicron variant. Unfortunately, the virus continues to evolve, and several worrisome new strains have taken hold across the United States recently.

In this week’s issue of Talking Therapeutics, we take a look at some of the latest data evaluating the effectiveness of our available vaccines against the various COVID-19 strains.

Point 1: New Bivalent Boosters Offer Only Modest Protection Against BA.5

The currently available bivalent boosters contain mRNA against both the ancestral strain and the BA.5 strain. These bivalent boosters were developed last winter and approved over the summer in 2022 despite robust in vivo data to support their effectiveness.

In this week’s issue of The New England Journal of Medicine, 2 new studies were published evaluating the bivalent boosters against the original monovalent boosters that were offered in 2021. The first study evaluated the antibody response for the bivalent boosters and found they did not elicit a discernibly superior antibody response against the BA.5 strain as compared with the original monovalent vaccines. The second study evaluated the immunogenicity of the available boosters and found T-cell responses increased only modestly after monovalent and bivalent mRNA boosting.

The authors attribute these disappointing results to imprinting, which means the immune system of the participants was primed to response to the ancestral strain by the initial COVID-19 vaccines from 2021. In order to overcome this barrier, monovalent vaccines containing only the new variant of interest may need to be developed.

Point 2: Meanwhile, BA.5 Is Losing Relevance

New variants such as BQ.1.1 and XBB have emerged as being even more immune evading than BA.5. A third study evaluating the effect of various boosters against these new strains was recently published. The study found patients who received 2 monovalent booster doses had antibody titers against BA.2.75.2, BQ.1.1, and XBB that were 23 to 63 times as low as that against the ancestral strain. In this study, the new bivalent boosters did perform better, with neutralization titers against BA.2.75.2, BQ.1.1, and XBB that were 12 to 26 times as low as that against the original strain that appeared in Wuhan.

Taken together, these 3 studies show the new bivalent boosters are better than their predecessors but only modestly. These results highlight the need for continued evolution in our approach to vaccine development against COVID-19.