While seeking to promote its COVID-19 vaccine booster shots, Moderna Inc. revealed that its first doses had shown a weakening efficacy a year after they were administered.

In a press release on Wednesday, Sept. 15, Moderna highlighted new data from its clinical vaccine trial, which suggests that “the Moderna COVID-19 vaccine is highly effective against circulating variants of concern, including in a vaccine effectiveness study conducted in partnership with Kaiser Permanente Southern California (KPSC) and in a separate recent publication by the U.S. Centers for Disease Control and Prevention (CDC).”

“It is promising to see clinical and real-world evidence adding to the growing body of data on the effectiveness of the Moderna COVID-19 vaccine,” the firm’s CEO Stéphane Bancel said, making its case for supporting booster shots.

“(The) Company believes data support benefit of an mRNA-1273 booster dose,” Moderna said in the news release.

However, the biotechnology company pioneering mRNA therapeutics and vaccines also unveiled that the protection from its COVID-19 vaccines offered a year ago is waning over time.

Its study documented 162 breakthrough cases in the participant group vaccinated over a year ago, while only 88 occurred in the group immunized during the early part of this year.

“The increased risk of breakthrough infections in COVE [phase 3] study participants who were vaccinated last year compared to more recently illustrates the impact of waning immunity and supports the need for a booster to maintain high levels of protection,” Bancel said.

Moderna said that its phase 3 clinical trial looked at breakthrough cases from July to August 2021.

With the new study, Moderna “believes this adds to evidence of potential benefit of a booster dose of mRNA-1273.”

Another vaccine maker, Pfizer, also seeks emergency approval from the U.S. Food and Drug Administration (FDA) to distribute its vaccine booster doses in the United States. Its third phase study of the shots found that 63.7% of the participants experienced fatigue, 48.4% had headaches, and 39.1% felt muscle pain after getting its COVID-19 vaccine boosters.

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