SAN ANTONIO — The Moderna vaccine generated nearly triple the COVID-19 antibodies that Pfizer's vaccine created in a new study published to the Journal of the American Medical Association.
The research examined 1,647 Belgian health care workers 6-10 weeks after they were inoculated with either of the shot series.
Previously uninfected doctors and nurses who took Moderna's doses produced 3,836 antibody units per milliliter. Previously uninfected doctors and nurses who took the Pfizer vaccine produced 1,444 antibody units per milliliter.
The Moderna shot outperformed Pfizer's in participants who were previously infected, as well.
But doctors are not yet certain whether the new data is medically relevant.
"Both shots generate more than enough antibodies to protect you," Dr. Michael Almaleh, medical director for WellMed's vaccine sites, said Tuesday. "Antibodies don't tell the whole story."
Almaleh notes that the body uses other tools, including cell-generated immunity, to fight off infections. It is possible, he said, that Pfizer's vaccine boosts cellular immunity more than Moderna's.
He added that scientific limitations make it harder to compare the vaccines' impacts on cellular immunity.
It is almost impossible to distinguish between the two mRNA vaccines' overall performance against the virus, according to Centers for Disease Control data. Moderna's shot is slightly more effective, though the gap between the two is negligible.
"They both work extremely well," Almaleh said, making reference to a CDC study on previously vaccinated people in Massachusetts who caught the virus anyway. "There were very similar numbers of individuals who had Moderna versus Pfizer that had breakthrough infections."
The Belgian study suggests the antibody concentration may be higher in Moderna's vaccine because the Moderna series contains a greater amount of vaccine. It's not clear why Moderna's vaccine requires more material.
Vaccine makers have published their shots' ingredients, but will not publish their shots' recipes. Because the companies will not reveal exactly how they produce their vaccines, it is hard to compare each company's doses.
Scientists will have to conduct more research to determine whether Moderna's shot is more effective, long-term. There is no evidence now that suggests a dramatic difference between the shots' efficacy.