Moderna said on Thursday its COVID-19 vaccine was about 93% effective through six months after the second dose, showing hardly any change from the efficacy reported in its original clinical trial.
However, the data does not include the vaccine's performance against the more contagious delta variant of the coronavirus, which has caused breakthrough infections among fully vaccinated people.
Given the variant's impact and expectations that antibody protection will eventually wane, the company said it expects booster shots will be needed this winter.
Moderna, along with Pfizer and German partner BioNTech, which make a similar messenger RNA-based vaccine, have been advocating for booster shots, even as public health officials call for more evidence that they are needed.
The fast-spreading Delta variant, now dominant in many countries, has caused surges in hospitalizations and deaths among the unvaccinated.
But reports of infections among vaccinated people and concerns about diminishing protection has increased pressure on wealthy nations to distribute booster shots, even as many countries struggle to access first vaccine doses.
Pfizer/BioNTech last week presented data showing their vaccine's efficacy waned about 6% every two months, declining to around 84% six months after the second shot. Pfizer has said it plans to seek U.S. authorization for a third shot later this month.
Moderna President Stephen Hoge said in an interview that the 93% efficacy data covers through March of this year.
"It looks like we've got durable efficacy," Hoge said. "But we are currently blind to what's been happening around Delta, and particularly around the explosion of cases that's happened in June and July."
Moderna Chief Executive Stephane Bancel said during a conference call the company will not be able to produce more than the 800 million to 1 billion vaccine doses it has already targeted for this year.
"We are not taking any more orders for 2021 because we are we are totally maxed out," he said.
The new Moderna data comes from the company's roughly 30,000-participant clinical trial used to gain emergency authorization for the vaccine in December.
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.
While the Pfizer/BioNTech and Moderna shots are similar, they are not identical. Moderna's doses contain 100 micrograms of vaccine, while Pfizer's contains 30 micrograms.
Moderna has been testing lower, 50-microgram dose versions of its vaccine as boosters. Studies of three different booster candidates induced robust antibody responses against variants, including Gamma, Beta and Delta, it said.
Moderna said neutralizing antibody levels following the boost approached those observed after the second shot.
Hoge said the higher dose of its vaccine may be playing a role in durability, but the company is pleased with protection seen in its lower-dose boosters. Moderna is also testing, and has not ruled out, a 100 microgram booster, he said.
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 https://www.reuters.com/business/healthcare-pharmaceuticals/pfizer-raises-estimates-2021-sales-covid-19-vaccine-335-bln-2021-07-28 to top $33.5 billion.
Moderna expects to finish its submission seeking full approval of the vaccine with U.S. regulators this month. Some people hesitant to get vaccinated have said they are wary of emergency approvals.
Moderna's shares touched a record high of $443.99 earlier on Thursday, bringing its market value to around $180 billion.