Researchers mix diluted blood plasma with viral samples, and then see whether it can grow in cell cultures. They figure out the concentration of plasma needed to neutralize all the virus.
2 doses of the vaccine produces plasma that can still neutralize the virus, but it requires 20x as much plasma on average. In turn, this means that the virus is more likely to be able to replicate and infect new cells before all the virus is neutralized.
However:
- There is still antibody efficacy against the virus, just not nearly as much.
- Memory B cells have a head-start at further developing specific immunity to new variants.
- This ignores the effect of T-cell mediated immunity.
- This mentions evidence that people who were previously infected and vaccinated have good neutralizing titers against Omicron.
- Other evidence suggests people who are boosted have much better neutralization titers against Omicron. That is, boosting doesn't just increase the number of antibodies, but increases the breadth of antibody protection.