A study from the Ragon Institute and other research institutions published in Cell found that an additional booster dose of mRNA COVID-19 vaccines (Moderna or Pfizer–BioNTech) is required to provide immunity against the Omicron variant. The standard vaccination regimen was found insufficient to generate antibodies capable of recognizing and neutralizing Omicron.

Following WHO designation of Omicron as a Variant of Concern (VOC) in November 2021, the Ragon Institute team constructed a harmless pseudovirus mimicking Omicron's spike protein, which carries 34 mutations. Working with collaborators at Massachusetts General Hospital, the researchers obtained blood samples from 239 fully vaccinated individuals (including 70 who had received a third booster dose of Pfizer or Moderna mRNA vaccines).

Results were striking: samples from individuals who received two mRNA vaccine doses or one J&J dose showed little neutralization of the Omicron pseudovirus, while those who received three mRNA vaccine doses demonstrated strong neutralization.

The mechanism remains unclear, but possibilities include:

• Booster doses generate antibodies that bind more tightly to the spike protein
• They induce antibodies targeting conserved regions of the spike protein common to all SARS-CoV-2 variants

While neutralizing antibody levels against Omicron were lower than those against the original strain or Delta, the findings strongly support the CDC recommendation for booster shots in individuals aged 16 and older.

Source: Garcia-Beltran WF, et al. mRNA-based COVID-19 vaccine boosters induce neutralizing immunity against SARS-CoV-2 Omicron variant. Cell. 2022. doi: 10.1016/j.cell.2021.12.033.