Moderna’s COVID-19 vaccines efficiency shows minimal decline six months after second shot

While its vaccine seems more “durable” six months on, warns booster likely needed with efficacy waning.

Alongside reporting an impressive set of second quarter results, Moderna has announced its two-shot messenger RNA-based COVID-19 vaccine’s efficacy was “durable” after only dropping by a percentage point to 93% for six months after the second shot – a minimal drop from 94% efficacy initially reported. "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," said Moderna’s CEO Stéphane Bancel. This comes a week after Pfizer and BioNTech announced their vaccine’s efficacy declined by around 6% every two months and eventually falling to about 84% roughly six months after the second shot was given - sparking debate about the need for booster shots. The duo’s vaccine is also based on mRNA technology.


However, Moderna also admitted the highly contagious Delta variant would likely lead to a spike in breakthrough infections among those who have been fully vaccinated. It also expects immunity against the virus to continue waning and thus eventually necessitating a booster shot in the Northern hemisphere before the winter. Moderna also highlighted results from a Phase II trial which showed a booster shot of its vaccine led to a “robust” antibody response against the three common variants, including the more transmissible Delta variant. In recent weeks, the Delta variant has dominated headlines and has spread to more than 100 countries, becoming the most dominant variant in the U.S. In the past few days alone, it has also led to new restrictions in China as authorities look to contain its spread.