Moderna’s booster shots against Covid-19 have shown robust antibody responses, according to results of Phase 2 clinical trials published on Thursday.

In the trial, Moderna tested a 50-microgram dose of three vaccine booster candidates in previously vaccinated individuals.

The findings showed that it induced robust antibody responses against the wildtype D614G Covid-19 strain and against important variants of concern including Gamma (P1); Beta (B1351); and Delta (B16172), the US pharmaceutical major said in a statement.

“Neutralising antibody levels following the boost approached those observed after primary vaccination with two doses of 100 micrograms of mRNA-1273,” it added. The data has been submitted to a peer-reviewed journal for publication.

The company added that its Covid-19 vaccine does not wane away and remains durable through six months after the second dose. The result of its clinical trial, which started in late July 2020 and recruited 30,000 volunteers, showing 94.1 per cent efficacy did not change much after six months, the company said in a statement.

“We are pleased that our Covid-19 vaccine is showing durable efficacy of 93 per cent through six months, but recognise that the Delta variant is a significant new threat so we must remain vigilant,” Moderna CEO Stephane Bancel said.

Moderna has also filed to the US Food and Drug Administration for a final approval of its vaccine on June 1, and expects to complete its submission in August.

The company is also conducting clinical trials of mRNA candidates across five therapeutic areas including infectious diseases, cardiovascular, oncology, rare disease, and autoimmune disorder.

“We have begun preparing late-stage studies for our flu vaccine and RSV vaccine, which received fast track designation from the FDA a few days ago and are looking forward towards our vision of a single dose annual booster that provides protection against Covid-19, flu and RSV for adults,” Bancel said.

On Thursday, the company also released its second-quarter earnings report. Moderna’s Covid vaccine generated $4.2 billion in sales in the three months ended June 30, the earnings report said.

Moderna said it aims to produce between 800 million to 1 billion Covid vaccine doses this year. It has also signed vaccine contracts worth $20 billion in sales this year and has agreements worth $12 billion in 2022, the statement said.