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Dec. 8, 2021:  Pfizer and BioNTech reported results from an initial laboratory study of their vaccine versus Omicron.

Quote:The third dose significantly increased the neutralizing antibody titers against the Omicron strain spike by 25-fold. Neutralization against the Omicron variant after three doses of the Pfizer-BioNTech COVID-19 vaccine was comparable to the neutralization against the wild-type strain observed in sera from individuals who received two doses of the companies’ COVID-19 vaccine: The geometric mean titer (GMT) of neutralizing antibody against the Omicron variant measured in the samples was 154 (after three doses), compared to 398 against the Delta variant (after three doses) and 155 against the ancestral strain (after two doses).

Apparently, the neutralizing titer against Omicron at this point after two doses was about 6 (154/25).  That seems extremely low to me.

I also interpret this to mean that the boosted effect against Omicron is similar to the waned effect of 6-month old two-shot regimen against Delta, but I may be wrong.