Moderna’s COVID-19 vaccine generates more than twice as many antibodies as a similar shot made by Pfizer and BioNTech, according to a new real-world study from a major Belgium hospital system.
The research, published Monday as a letter in the Journal of the American Medical Association, suggests that antibody levels among people who hadn’t been infected with COVID-19 before receiving two doses of the Moderna vaccine averaged 2,881 units per milliliter, compared with 1,108 units per milliliter in a similar-sized group who got the Pfizer-BioNTech shot.
A total of 1,647 people participated in the study. A group of 688 people were vaccinated with Moderna’s mRNA-1273 shots, while 959 received two shots of Pfizer’s BNT162b2. All of them are health care workers at the Ziekenhuis Oost-Limburg in Belgium, a tertiary care center.
The notable difference in antibody levels might be explained by a higher amount of mRNA content in the Moderna vaccine and the longer interval between doses, according to the study. Each Moderna dose contains 100 micrograms of active mRNA ingredient, while the Pfizer-BioNTech shot contains only 30 micrograms of similar content. The Moderna injections were administered four weeks apart, compared with three weeks for Pfizer-BioNTech.
A higher antibody level suggests that Moderna’s vaccine is more protective against breakthrough infections, or infections in people who have been fully inoculated.
The Moderna shots also appear to be more effective than Pfizer at blocking mutations of the coronavirus, such as the delta variant. A separate U.S. study released earlier this month found that Moderna’s overall effectiveness against COVID-19 dropped only slightly to 76 percent in July from the 86 percent recorded in January 2021 before the delta variant emerged, while Pfizer’s overall efficacy fell from 76 percent to 42 percent over the same period.
That study included more than 50,000 participants in the Mayo Clinic Health System.
Both Moderna and Pfizer are studying the effect of adding a third booster to their two-shot structure as breakthrough infections rise globally. The FDA is expected to authorize the additional booster shot in September. The agency has already approved a third booster shot for people with compromised immune systems.