U.S. biotechnology firm Moderna Inc. said Monday that its authorized COVID-19 vaccine is expected to be protective against emerging strains of the novel coronavirus first identified in Britain and South Africa.

But the company also said that it is advancing a vaccine booster candidate against the South Africa variant into preclinical studies, seeking to determine whether it will be more effective to strengthen antibodies against the variant and potential future variants.

A scientist works in the lab at Moderna in Cambridge, MA on Feb. 28, 2020. (The Boston Globe/Getty/Kyodo)

"As we seek to defeat the COVID-19 virus, which has created a worldwide pandemic, we believe it is imperative to be proactive as the virus evolves," Moderna CEO Stephane Bancel said in a press release, adding that the booster candidate will be developed "out of an abundance of caution."

According to the company, an in-vitro study showed that the vaccine's effectiveness did not show any significant impacts from the British variant. But with the South Africa variant, there were signs suggesting "a potential risk of earlier waning of immunity" to the new strains.

Moderna's two-dose vaccine was put into practical use in the United States in December, following the rollout of a vaccine manufactured by U.S. pharmaceutical giant Pfizer Inc. and its German partner BioNTech SE. Some other countries have also authorized the use of the vaccines.

Both the Moderna and Pfizer vaccines use a new technology known as messenger RNA, or mRNA.

While traditional vaccines put a weakened or inactivated germ into human bodies to trigger an immune response, mRNA vaccines give instructions for cells to make a harmless "spike protein" that resembles one found in the novel coronavirus.

The immune system then detects the protein and starts building an immune response and making antibodies to protect against future infection.

The Japanese government has an agreement with Moderna for enough vaccine doses to cover 25 million people.