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(NEXSTAR) — The Moderna COVID-19 remains effective even after 6 months, the company said in a Tuesday update on its ongoing clinical trials.

The study looked at 33 healthy adult participants in the Phase 1 study of Moderna’s vaccine at six months following the final dose.

Multiple analyses determined that COVID-19 antibodies persisted for at least six months after the second dose, the company said in a press release. The vaccine’s efficacy was found to be greater than 90 percent against all COVID-19 cases and greater than 95 percent against severe cases of the virus.

Moderna also noted it was testing booster vaccines, which may be necessary to fight variants, and that it would be submitting preclinical data for peer review.

The boosters it’s developing will help fight the B1351 variant, sometimes called the South African variant.

The company said it delivered about 17 million doses to the U.S. government in the fourth quarter of 2020 and was on track to deliver another 100 million doses by the end of May 2021.