Moderna vaccine 93% effective six months after second dose

Moderna said on Thursday its COVID-19 shot was about 93 per cent effective through six months after the second dose.

It said the vaccine showed hardly any change from the 94 per cent efficacy reported in its original clinical trial.

However, the company added that it still expects booster shots to be necessary ahead of the winter season as antibody levels are expected to wane.

Moderna and rival Pfizer and BioNTech have been advocating a third shot to maintain a high level of protection against COVID-19.

During a second-quarter earnings call, Moderna CEO Stephane Bancel said that the company would not produce more than the 800 million to 1 billion doses of the vaccine that it has targeted this year.

"We are now capacity constrained for 2021, and we are not taking any more orders for 2021 delivery," he said.

Moderna shares fell 3.6% to around $403.87 in pre-market trading after closing at $419.05 on Wednesday.

The Moderna data compares favourably to that released by Pfizer and BioNTech last week in which they said their vaccine's efficacy waned around 6 per cent every two months, declining to around 84 per cent six months after the second shot.

Both the Moderna and Pfizer-BioNTech vaccines are based on messenger RNA (mRNA) technology.

"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," Bancel said.

The comment comes as public health officials across the world debate whether additional doses are safe, effective and necessary even as they grapple with the fast-spreading Delta variant of the coronavirus.

Meanwhile, Pfizer is planning to seek authorisation for a third shot later this month, and some countries have begun or plan to start administering a booster shot to older or vulnerable people.