Updated COVID-10 booster shots are rolling out across the United States, and these new bivalent formulations target the omicron BA.4 and BA.5 subvariants that have become the dominant circulating strains as well as the original form of the coronavirus.

UConn Health's Dr. David Banach, an infectious diseases physician and hospital epidemiologist, spoke with UConn Today about the latest CDC vaccination guidelines and the significance of these updated boosters:

What’s the difference between the monovalent and bivalent vaccines?

The monovalent vaccines are the ones that have been available thus far. They contain a small piece of the mRNA component of the virus based on the original SARS-CoV-2 virus, sometimes termed as the “ancestral strain,” and are designed to generate an immune response to that original virus.

We’ve seen with the omicron variant — and specifically with the BA.4 and BA.5 subvariants, which have appeared most recently — the virus has changed. The bivalent vaccine contains both the portion of the original ancestral virus mRNA as well as a portion of mRNA that is specific for the BA.4 and BA.5 subvariants that have been circulating most recently. The hope is, by more specifically targeting the most recent subvariants, the bivalent boosters will reduce the impact of COVID both on individuals who received them as well as the population.

Conceptually it’s analogous to what has been done with the influenza vaccine. The technology’s a little different but it’s based on the same idea. It’s targeted against both the original strain and the BA.4 and BA.5 subvariants of omicron.

What becomes of the monovalent vaccine?

At this time the vaccination program will be a primary vaccine series with the original monovalent vaccine and booster doses using the bivalent vaccine.

Why wouldn’t we just start people with the bivalent vaccine?

Data showed the monovalent vaccine upfront provides that high level of protection. The bivalent vaccine has not been evaluated as a primary vaccine candidate, so we don’t have the data to support its use in that context. That’s how it was originally designed, to be a booster.

Dr. Banach is a leading voice on the fight against the COVID-19 virus, and he's available to speak with the media. Click on his icon to arrange an interview today.