Efficacy of mRNA vaccines drops to 66% against Delta variant – US study

PHOTO: Wikimedia

A large study carried out by the US Centres for Disease Control and Prevention shows that the efficacy of mRNA vaccines drops from 91% to 66% against the Delta variant. The study involved thousands of healthcare staff and other frontline workers across 6 states. Participants were tested once a week and tested again if they developed Covid-19 symptoms, thereby allowing researchers to determine the efficacy of mRNA vaccines against symptomatic and asymptomatic infection.

During the period of December 14, 2020 to April 10, 2021, before the highly-contagious Delta variant became the dominant strain, the vaccines demonstrated an efficacy of 91%. However, in the weeks that followed that period, up to August 14, that efficacy rate fell to 66%.

However, researchers have pointed out that some of this could be attributed to the fact that the protection offered by vaccines will decline over time anyway, and that the 66% rate was based on quite a short study period, involving fewer cases. They emphasise the ongoing importance of vaccination.

“Although these interim findings suggest a moderate reduction in the effectiveness of Covid-19 vaccines in preventing infection, the sustained two thirds reduction in infection risk underscores the continued importance and benefits of Covid-19 vaccination.”

Related news

This latest study follows a number of others that have also shown a drop in vaccine efficacy when dealing with the Delta variant, although the drop differs from study to study. What appears to remain stable however, is the protection offered against serious illness, which remains at over 90%, according to a recent New York study.

Meanwhile, a similar study of patients in Los Angeles shows that unvaccinated people are over 29 times more likely to end up in hospital with Covid-19 compared to vaccinated people. This equates to an efficacy of around 97%.


Covid-19 News

Maya Taylor

A seasoned writer, with a degree in Creative Writing. Over ten years' experience in producing blog and magazine articles, news reports and website content.

Related Articles