Moderna said Thursday that protection from its Covid-19 vaccine remained strong for at least six months, and the variant-specific boosters shot it is testing generated a "robust" antibody response to Delta.

In a final analysis from its Phase 3, or final stage, clinical trial, Moderna's Covid vaccine showed 93 percent efficacy at six months following the second dose.

The company is also carrying out clinical trials on three different Covid-19 boosters, with all of them producing high antibody levels against the original coronavirus strain and variants of concern, including Delta, originally identified in India.

"We are pleased that our COVID-19 vaccine is showing durable efficacy of 93% through six months, but recognize that the Delta variant is a significant new threat so we must remain vigilant," said CEO Stephane Bancel in a statement.

The statement added that Moderna expects to file its submission for full approval of its Covid vaccine with the US Food and Drug Administration this month.

The company has also begun studies for several other vaccines, including the flu, Zika, respiratory syncytial virus and others, and is developing a Covid vaccine that can be stored at fridge temperature.