Moderna Says Booster COVID-19 Shots May Be Required, Citing New Data on Breakthrough Cases

'Waning immunity' noted: Moderna CEO
By Mimi Nguyen Ly
Mimi Nguyen Ly
Mimi Nguyen Ly
Mimi Nguyen Ly is an assignment editor and world news reporter based in Australia. She has a background in optometry. Contact her at
September 15, 2021 Updated: September 16, 2021

Moderna announced on Wednesday that its COVID-19 vaccine decreases in efficacy after a year, suggesting a potential benefit in having a booster shot of its mRNA vaccine.

New clinical trial data showed that breakthrough COVID-19 infections are less common among people who received Moderna’s vaccine, mRNA-1273, more recently compared to less recently, the company said in a release.

The company was relaying findings from a data analysis of over 14,000 people at median eight months after their first dose and over 11,000 people at median 13 months after their first dose. The study is awaiting peer review.

Researchers found that in July-August, around the time when the Delta strain of the CCP (Chinese Communist Party) virus was regarded as the predominant strain, there were 88 CCP virus breakthrough cases in the cohort vaccinated more recently (49.0 cases per 1,000 person-years) compared with 162 cases among the cohort vaccinated earlier (77.1 cases per 1,000 person-years).

Overall, only 19 cases were considered severe in the study. There was also a lower rate of severe cases among those more recently vaccinated, but the finding was not statistically significant, Moderna noted.

Moderna CEO Stéphane Bancel said in a statement that the analysis “illustrates the impact of waning immunity and supports the need for a booster to maintain high levels of protection.”

The company said its vaccine is still “highly effective against circulating variants of concern,” citing a separate study that it conducted in partnership with Kaiser Permanente Southern California health system, as well as recently-published data from the U.S. Centers for Disease Control and Prevention that suggested high vaccine efficacy among those who received the Moderna shot compared to other COVID-19 vaccines.

Moderna on Sept. 1 applied for authorization from the U.S. Food and Drug Administration for the booster, or third dose, of its COVID-19 vaccine, to be given six months after the second dose.

Officials from the FDA and the World Health Organization said in a paper published in the Lancet medical journal on Monday (pdf) that so far there is no evidence that the general population needs booster shots against the CCP virus.

They also warned that if booster shots are given too soon, side effects may be observed in the general population—a poorly understood phenomenon. They wrote that the immune-mediated side-effects may include “myocarditis, which is more common after the second dose of some mRNA vaccines, or Guillain-Barre syndrome, which has been associated with adenovirus-vectored COVID-19 vaccines.”

“Even if boosting were eventually shown to decrease the medium-term risk of serious disease, current vaccine supplies could save more lives if used in previously unvaccinated populations than if used as boosters in vaccinated populations,” the authors wrote.

Mimi Nguyen Ly
Mimi Nguyen Ly is an assignment editor and world news reporter based in Australia. She has a background in optometry. Contact her at