Moderna has said its Covid-19 vaccine was about 93 per cent effective through six months after the second dose, showing hardly any change from the 94 per cent efficacy reported in its original clinical trial.
However, the company said it still expects booster shots to be necessary ahead of the winter season as antibody levels are expected to wane.
It and Pfizer and partner BioNTech, which make a similar messenger RNA-based vaccine, have been advocating for a third shot to maintain a high level of protection against Covid-19, especially as more contagious variants of the virus spread widely.
Moderna chief executive Stephane Bancel said during a conference call that the company would not be able to produce more than the 800 million to 1 billion doses of the vaccine it has already targeted for this year.
“We are not taking any more orders for 2021 because we are totally maxed out,” he said.
The new Moderna data comes from the company's roughly 30,000-participant clinical trial used to support the vaccine's emergency authorisation in December.
Durable efficacy
It compares favourably to data from Pfizer and BioNTech last week that showed their vaccine's efficacy waned about 6 per cent every two months, declining to around 84 per cent six months after the second shot.
While the shots are similar, they are not identical. Moderna's doses contain 100 micrograms of vaccine, while Pfizer's contain 30 micrograms.
“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,” Bancel said.
The six-month data also suggests that Moderna's vaccine still provides 98 per cent protection against severe disease and was 100 per cent effective at preventing death caused by Covid-19. There were three deaths in the placebo arm of the trial.
Public health officials around the world are debating whether additional vaccine booster doses will be necessary as they grapple with the fast-spreading Delta variant of the coronavirus that has become dominant in many countries, leading to a surge in cases and hospitalizations, especially among the unvaccinated.
Pfizer has said it is planning to seek authorisation for a third shot later this month. Some countries like Israel and Germany have begun or plan to start administering booster shots to older or vulnerable people.
Booster candidates
Moderna said its studies of three different booster candidates induced robust antibody responses against variants, including Gamma, Beta and Delta.
It said neutralizing antibody levels following the boost approached those observed after the second shot.
For this year, Moderna has signed vaccine contracts worth $20 billion in sales. It has agreements for $12 billion in 2022, with options for another roughly $8 billion in sales, and expects to produce between 2 billion and 3 billion doses next year.
The company has not been able to keep pace with much larger Pfizer, which expects to manufacture as many as 3 billion doses this year and 2021 sales to top $33.5 billion.
Moderna's vaccine was authorised for emergency use in adults in the United States in December and has since been cleared for emergency or conditional use in adults in more than 50 countries.
The company expects to finish its submission for full approval with the US Food and Drug Administration this month.
