Studies suggest current vaccines boost immune response against Omicron

Despite being developed to fight the original COVID-19 strain, a third dose of mRNA vaccine boosts the immune system substantially to better fight infections caused by the Omicron variant relative to the standard 2-dose primary series, according to two new studies in Nature and JAMA Network Open.Broader B-cell memory responseOne mechanism by which the booster dose fights Omicron is by increasing the range of memory B cells in the recipient, the Nature researchers write.

The B cells then help produce broadly neutralizing antibodies, more than 50% of which were capable of neutralizing Omicron in a study of 42 adult volunteers.To conduct the study, researchers assessed the longitudinal immune responses of volunteers who received the primary two-dose vaccine series plus a booster shot.

None of the volunteers—all healthy adults—had previously been infected with any strain of SARS-CoV-2. The study took place in 2021, with 34 volunteers receiving the Pfizer-BioNTech vaccine and 8 receiving the Moderna vaccine.Blood samples were taken 2.5 weeks after the prime dose, 1.3 and 5 months after the second dose, and 1 month after the third dose.

Following a 7.3-fold decrease in neutralizing titers between 1.3 and 5 months after the second vaccine dose, administration of a booster dose raised neutralizing titers 11.9-fold, the authors found.To determine how neutralizing antibodies after the booster dose held up against different strains of the virus, the researchers compared 18 antibody pairs that were randomly selected across participants and had measurable neutralizing activity against the original virus strain.