The 3rd and 4th boosters are not tweaked for the new variants. They are same as the first two that were developed for the original variant. That's why the Pfizer Ceo was saying they'll be bringing one out in April for omicron but they haven't. Any new jab for new variant would have to go thru a new clinical trial. Or it should.
There is a video of Bourla talking about the jabs against omicron from earlier this year where he raises some doubt of their efficacy. It's where he talked about Pfizer working on the new booster.
