Moderna Inc. has released a set of data which suggested its Covid-19 vaccine is effective in preventing serious health issues or death from "variants of concern" but admitting that efficacy decreases over time, such that those who received the vaccine last year were twice more likely to contract a breakthrough case of the coronavirus disease.

According to the data, which Moderna released Wednesday, a "study shows lower risk of breakthrough infection in participants vaccinated more recently (median 8 months after first dose) than participants vaccinated last year (median 13 months after first dose)."

A Moderna trial conducted over the summer, labeled Phase 3 COVE Study, revealed that "88 breakthrough cases of COVID-19 occurred in the more recently vaccinated group (49.0 cases per 1000 person-years) compared to 162 cases in the group vaccinated last year (77.1 cases per 1000 person-years)."

Across both groups, Moderna highlighted that "only 19 severe cases were observed." While there was a "numerical trend toward a lower rate of severe cases in the groups vaccinated more recently." Moderna insisted that the number of cases was low enough that the trend was "not significant."

The research found that those who were vaccinated earlier on had a 50% higher rate of symptomatic breakthrough cases during the months of July and August compared to those who had received the vaccination later.

In a statement issued along with the data, Moderna CEO Stéphane Bancel insisted that the data "supports the need for a booster" shot.

"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evidence adding to the growing body of data on the effectiveness of the Moderna Covid-19 vaccine," Bancel said of the unpublished analysis. "The increased risk of breakthrough infections in COVE 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.

Moderna has also requested authorization from the U.S. Food and Drug Administration for a third-dose booster shot, which will be one-half the dose of its existing vaccine.

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