Pfizer’s two omicron-focused booster vaccines massively improve a person’s immune response against the COVID variant, the company said Saturday. Across clinical trials involving more than 1,200 people, Pfizer tried two different omicron boosters: one focused solely on the omicron variant (called a monovalent vaccine) and one that used Pfizer’s initial vaccine but tweaked it to also combat omicron (called bivalent). The monovalent booster increased immune response between 13- and 19-fold, a massive increase that varied based on the dose size. The bivalent shot boosted immune response between 9-…