Moderna's (MRNA  ) mRNA COVID-19 vaccine generated more than double the antibodies when compared to a similar shot developed by Pfizer (PFE  )-BioNTech (BNTX  ), based on a new letter to the Journal of the American Medical Association.

The study of almost 2,500 health care workers at a major Belgium hospital system found that antibody levels among employees who had no history of COVID infection before getting both doses of the Moderna vaccine averaged 2,881 units per milliliter, while those who received both Pfizer-BioNTech shots averaged 1,108 units.

The study also found that antibody levels negatively correlated with age among participants, with the highest levels seen in those younger than 35 years old. Still, regardless of age, participants who received the Moderna vaccine had higher antibody levels compared to those vaccinated with the Pfizer-BioNTech shot.

The results, published in the letter on Monday, suggested that the key differences between the two similar vaccines may be explained by the higher amount of active ingredient that Moderna uses in its shot--100 micrograms compared to Pfizer-BioNTech's 30--and the longer dosing interval between the two doses--four weeks for Moderna versus three weeks for Pfizer-BioNTech.

Regardless of which vaccine an individual chooses to protect against the coronavirus, however, new data presented to a Centers for Disease Control and Prevention committee showed more evidence that the COVID vaccines used in the United States (Moderna, Pfizer-BioNTech, and Johnson & Johnson (JNJ  )) provide high levels of protection against severe disease, according to the New York Times.

Dr. Sara Oliver, a CDC scientist, presented unpublished data from COVID-net, a hospital surveillance system, to the CDC committee's meeting on Monday, the NYT reports, showing data that all three vaccines remained highly effective at preventing hospitalizations from April through July. The data also suggests that all three vaccines are effective against the highly contagious Delta variant, which became the dominant strain in the U.S. during the summer months.

Oliver said that for adults under the age of 75, the vaccines were at least 94% effective at preventing hospitalizations, NYT reports. Moreover, while protection did wane for those aged 75 years and older, it still remained above 80%.

Both new sets of vaccine data come as the U.S. is debating the need for nationwide COVID booster shots ahead of the coming colder seasons. The data presented before the CDC committee did suggest that protection against infection or mild disease does appear to have declined throughout the data, which would suggest the need for booster shots in the near-term.