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(NEXSTAR) – The Moderna COVID-19 vaccine remains effective even after six months, the company said Tuesday.

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

Multiple analyses determined that COVID-19 antibodies persisted for at least six months after the second dose, the company said. The vaccine’s efficacy was found to be greater than 90% against all COVID-19 cases and greater than 95% 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 submit preclinical data for peer review.

The boosters could help fight the B.1.351 strain, known as the South African variant.

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