Many people find themselves unsure whether to wait on new, updated formulations of the COVID-19 vaccines or to mix and match combinations of the original vaccine strains.

Each of the existing and upcoming vaccines relies on emulating the spike protein to trigger the immune response.

Moderna’s new bivalent vaccine mixes mRNA that encodes for the spike proteins of the original SARS-CoV-2 virus as well as the slightly different spike protein of the more infectious omicron variant.

In early June 2022, Moderna said that in clinical trials, its bivalent vaccine outcompetes the original vaccine strain, inducing a stronger immune response and longer protection against the original SARS-CoV-2 and its variants, including omicron.

And most recently, on June 25, Pfizer-BioNTech also announced results for its two new COVID-19 vaccine formulations: a bivalent formulation consisting of mRNA that encodes for the spike proteins of the original SARS-CoV-2 strain and the original BA.1 omicron subvariant, and a “monovalent” version that is only directed at the spike protein of BA.1.

Another vaccine formulation that is working its way toward authorization is Novavax, a vaccine built using the spike protein of the original SARS-CoV-2 virus.

For example, recent studies suggest that when adults who were fully vaccinated with any of the original three COVID-19 vaccines – Pfizer-BioNTech, Moderna or Johnson & Johnson – received a booster dose with a different vaccine brand from the one they received in their initial series, they had a similar or more robust immune response compared to boosting with the same brand of vaccine

The reason why mixing vaccines might produce a more robust immune response goes back to how each one presents the spike protein of the virus to the immune system