Moderna said on Dec. 20 that its existing COVID-19 vaccine booster shot sharply increased Omicron neutralizing antibody levels in laboratory testing, with the drugmaker adding that it continues to work on an Omicron-specific booster. The company said in a statement that its currently authorized 50 microgram dose booster of its mRNA-1273 vaccine increased Omicron neutralizing antibody levels 37-fold, while a not-yet-approved 100 microgram dose booster raised them 83-fold. Moderna said researchers observed a “trend toward slightly more frequent adverse reactions” with the higher booster dosage, comparable to those seen after the two-dose primary regimen, characterizing it as “generally safe and well tolerated.” Moderna’s 50 microgram COVID-19 booster was authorized in October, with the company’s first two shots being 100 microgram doses. While Moderna continues to work on developing an Omicron-specific third shot, called mRNA-1273.529, the firm said it considers its existing booster the “first line of defense” against the Omicron variant …