Why Does the Omicron Booster Contain the Wuhan Strain? No, It’s Not for Higher Protection

On August 31, 2022, the U.S. Food and Drug Administration (FDA) amended the emergency use authorizations (EUAs) of the Moderna COVID-19 vaccine and the Pfizer-BioNTech COVID-19 vaccine to authorize the use of bivalent COVID-19 vaccines manufactured by both the companies as a single booster dose.

These bivalent vaccines contain the mRNA components of both the spike genes of SARS-CoV-2 virus ancestral strain and the BA.4/5 subvariants. However, the ancestral strain has long disappeared. So why should the new booster vaccines still incorporate half of the original strain’s mRNA, when the Omicron variants are currently the most prevalent?

What Are These Updated Boosters?

These bivalent vaccines are called “updated boosters” by the FDA. They contain two messenger RNA (mRNA) components of the SARS-CoV-2 virus, which is the culprit of the COVID-19 pandemic. One component is the ancestral strain of SARS-CoV-2, which was isolated and sequenced from Wuhan, China; and the other is the mRNA shared by the BA.4 and BA.5 sub-lineages of the Omicron variant.