A study into the immune responses of the two mRNA COVID-19 vaccines found that Moderna’s vaccine created twice as many antibodies as the Pfizer-BioNTech vaccine.
Researchers analyzed the antibody levels of Belgium health care workers after they received both doses of the vaccines, including 688 vaccinated with Moderna and 959 who received the Pfizer shots, in the study published in the Journal of the American Medical Association on Monday.
Among those who had not been previously infected, the Moderna recipients averaged 2,881 units per milliliter, compared to the Pfizer recipients who counted 1,108 units per milliliter.
Participants who previously contracted COVID-19 reported higher antibody levels, raising the overall average among all participants to 3,836 units per milliliter for Moderna and 1,444 units per milliliter for Pfizer.
The antibody levels in those who received Moderna were higher in infected, uninfected and across age categories, according to the study.
The researchers said the difference in antibody levels could potentially be attributed to the higher mRNA content within the Moderna vaccine and the longer interval between the initial and second shots. The second vaccine of Moderna is given four weeks after the first shot, while the Pfizer vaccine is administered three weeks following the initial shot.
The antibody testing was conducted before vaccination and six to 10 weeks after the second dose. The study found the levels to be negatively correlated with age in those who hadn’t been previously infected, with the highest antibody levels among those younger than 35.