Moderna’s results show that the currently authorized booster dose of 50 micrograms — half the dose given for primary immunization — increased the level of antibodies by roughly 37-fold, the company said. A full dose of 100 micrograms was even more powerful, raising antibody levels about 83-fold compared with pre-boost levels, Moderna said.

Both doses produced side effects comparable to those seen after the two-dose primary series. But the dose of 100 micrograms showed slightly more frequent adverse reactions relative to the authorized 50-microgram dose…

Moderna tested a third shot of several versions of its vaccine, each in 20 people. Before boosting, all the individuals had low levels of antibodies that can prevent Omicron infection. At Day 29, after receiving a third shot, the 50-microgram and 100-microgram doses of the current vaccine both sharply increased antibody levels.

The company also tested “multivalent” booster shots that incorporate mutations seen in the Beta and Delta variants, many of which are also present in Omicron. Those continuing trials each have 300 to 600 people enrolled in them. The 50-microgram and 100-microgram doses of the multivalent boosters increased antibody levels to similarly high levels, Moderna said.