(Photo: Reuters)

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

Moderna 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 said it 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.

The six-month data also suggests that Moderna's vaccine still provides 98% protection against severe disease and was 100% effective at preventing death caused by COVID-19.