Moderna COVID-19 Vaccine Remains Effective for 5.3 Months After Second Dose


It demonstrated 93.2% efficacy 14 days afterward and greater than 90% for 4 or more months.

The Moderna mRNA-1273 COVID-19 vaccine remains effective and safe for an average of 5.3 months after individuals receive the second dose, results of a clinical trial published in the New England Journal of Medicine showed.

The Coronavirus Efficacy (COVE) trial included 30,420 individuals at 99 US sites who were at severe risk of COVID-19 or whose location or circumstances put them at risk of COVID-19.

From July 27 to October 23, 2020, individuals were randomly assigned their first dose, with their follow-up 28 days after.

“Overall, we observed lower incidence rates of COVID-19 cases in July and August among participants vaccinated more recently, but it’s important to keep in mind that the numbers we are seeing are far from a decay back to original risk,” Lindsey Baden, MD, physician at the Division of Infectious Diseases at Brigham and Women’s Hospital, said in a statement.

After the FDA granted Moderna’s vaccine emergency use authorization, the COVE trial was amended to include 2 parts that monitored individuals who had already received the vaccine and administered the vaccine to those who received the placebo.

“The rapid redesign of the COVE study allowed us to successfully maintain participants in the study and will allow us to study longer-term safety and efficacy,” Baden said. “Using established and novel study methods, we’ve been able to continue to compare outcomes for those who were vaccinated earlier versus later in the study population.”

After 14 days since the second dose, investigators found that the vaccine was 93.2% effective against COVID-19 compared with the placebo group.

Prevention remained consistent throughout the follow-up, with efficacy greater than 90% 4 or more months after the second dose.

“Overall, our results continue to demonstrate that vaccines work and work extremely well at preventing COVID-19,” Baden said.

“We are continuing to explore questions about duration of immunity following vaccination and the impact of variants. But even as we examine the possibility of waning immunity, we see evidence that the vaccine is still very protective,” Baden said.

Safety was also continuously assessed in the group, with adverse events 7 days after vaccination, such as fatigue, headaches, joint pain, and muscle aches.

Vaccine efficacy was also high in individual subgroups such as aged 65 years or older, aged 75 years or older, different ethnical and racial groups, individuals with comorbidities, and those with occupational risk exposure.

“The message here is not that if you were vaccinated early, you’re not protected. Those vaccinated more recently may be experiencing a marginal improvement, but both groups are benefitting from protection compared to people who remain unvaccinated,” Baden said.

The same group of investigators also published results on MedRxiv that explored the analysis of individuals who received the vaccine between July and December 2020 and those who received the placebo between December 2020 and March 2021.


Phase 3 trial results: mRNA-1273 vaccine continued to be safe and efficacious more than five months after second dose. EurekAlert. News release. September 22, 2021. Accessed September 23, 2021.

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