Moderna vaccine is durable through 6 months, booster needed by winter, says company

Moderna’s mRNA coronavirus vaccine remains at a high 93% efficacy for six months after the second dose, but company officials said a booster shot will likely be needed by winter due to the delta variant and seasonality of the virus.

The Cambridge-based biotech company announced its six-month data on Thursday, which also showed Phase 2 trial studies of three different Moderna booster shots that triggered antibody responses against coronavirus variants including the ultra-contagious delta variant.

“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,” reads a statement from Moderna CEO Stephane Bancel.

In a presentation to investors on Thursday, the company’s booster strategy took into account the delta variant, coronavirus seasonality and public fatigue of non-pharmaceutical measures such as mask-wearing and social distancing.

“Given this intersection, we believe dose 3 booster will likely be necessary prior to the winter season,” the presentation stated.

The issue of booster doses has stirred up debate in the medical community in recent weeks.

Some countries such as Israel, France and Germany have already begun offering booster doses while other nations including the United States have held off.

The head of the World Health Organization called Wednesday for a moratorium on administering booster shots of COVID-19 vaccines as a way to help ensure that doses are available in countries where few people have received their first shots.

Dr. Shira Doron, infectious disease physician at Tufts Medical Center said she agrees with the WHO moratorium, adding that the vaccines are remaining incredibly effective with minimal signs of waning immunity.

Doron said we will likely need a booster shot at some point, but that may not even be necessary for years.

“You have to be watching for waning effectiveness, but waning effectiveness over time that actually leads to severe disease,” Doron told the Herald.

Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said a decision about boosters will be made “based on a complication of evidence” such as immune response, clinical trial data and effectiveness in diverse populations such as health care workers.

“It will be a combination of all that evidence that helps inform our booster strategy,” Walensky said during a Thursday White House briefing.

Immunocompromised people are vulnerable even after vaccination, as they do not generate an adequate antibody response, according to Dr. Anthony Fauci, the nation’s top infectious disease specialist.

That population could benefit from a third dose. “So in this regard, it is extremely important for us to move to get those individuals their boosters and we are now working on that,” Fauci said.

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