(WXIN) – Moderna released information this week indicating protection from its COVID-19 vaccine wanes over time as U.S. regulators try to determine the need for booster shots.

The U.S. drugmaker shared information from a phase three study showing that breakthrough cases were less frequent in those who’ve been more recently vaccinated.

Researchers compared about 14,000 people in Moderna’s 2020 vaccine study who had gotten a first dose about a year ago with another 11,000 vaccinated last winter, roughly eight months ago. As delta surged in July and August, Moderna concluded the more recently vaccinated group had a 36% lower rate of “breakthrough” infections compared with those vaccinated longer ago.

According to Moderna’s data, there were 88 breakthrough cases out of 11,431 people vaccinated between December 2020 and March 2021. The company identified 162 breakthrough cases out of 14,746 people vaccinated in July 2020 through October 2020.

There were also fewer severe cases of COVID-19 in individuals who had been more recently vaccinated, Moderna said.

The company believes the results show the need for booster shots, as the vaccine’s efficacy appears to wane over time. The analysis still needs to be peer reviewed.

Pfizer-BioNTech is also seeking approval of an additional booster shot of its COVID-19 vaccine. A key Food and Drug Administration vaccine advisory panel will convene this week to examine the need for booster shots in the U.S.

Pfizer said protection against COVID-19 is holding in the U.S. However, the company gave an extra dose to 306 people six to eight months after they received their second dose; the booster shot resulted in a threefold increase in virus-fighting antibodies.

Support for the booster shot has been mixed. While the Biden administration hoped to begin distributing doses on Sept. 20, the FDA has taken a cautious tone thus far. The agency will have the final say on the booster campaign and doesn’t necessarily have to follow the recommendations of its advisory panel. Booster shots have been approved for individuals with compromised immune systems.

The Associated Press contributed to this story.