Moderna: Vaccine 93% effective up to 6 months but booster likely needed before winter

CAMBRIDGE, Mass. - Moderna’s COVID-19 vaccine remained 93% effective against symptomatic illness six months after the second dose, but amid the ongoing spread of the highly contagious delta variant, the company said it believes a booster dose will be necessary prior to the winter season. 

The company announced the findings Thursday ahead of an earnings call, which also said its vaccine booster candidates produced a "robust" immune response against the delta variant.

Moderna said it believes the ongoing spread of the delta strain combined with more people gathering indoors as it gets colder will "lead to an increase of breakthrough infections in vaccinated individuals." 

"While we see durable Phase 3 efficacy through 6 months, we expect neutralizing titers will continue to wane and eventually impact vaccine efficacy," the company said. "Given this intersection, we believe dose 3 booster will likely be necessary prior to the winter season."

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The vaccine’s latest 93% effectiveness figure is just short of the shot’s initial reported efficacy of 94%. Moderna said data shared Thursday was collected from an analysis of its large clinical trial that began in July of 2020 and was completed before the delta variant became the dominant strain in the U.S. 

"We are pleased that 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," Moderna CEO Stephane Bancel said in a statement.

FILE - A health worker shows a bottle of Moderna Covid-19 vaccine for medical staff at Adam Malik hospital on Aug. 4, 2021, in Medan, Indonesia. (Photo by Ivan Damanik/NurPhoto via Getty Images)

Moderna’s booster shot candidates also showed "robust antibody responses" to the delta variant, as well as other COVID-19 variants of concern, in a Phase 2 study, according to the company. The data have been submitted to a peer-reviewed journal for publication.

Moderna has stated the rolling submission process for full approval of its two-dose vaccine by the U.S. Food and Drug Administration and said it expects to complete its submission this month.

"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 added.

To date, nearly 140 million doses of Moderna’s COVID-19 vaccine have been administered in the U.S.

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This story was reported from Cincinnati.