Research published in JAMA found the Moderna’s COVID-19 vaccine drove an antibody response that was more than two times greater than that of Pfizer’s.

Specifically, the Moderna mRNA-1273 vaccine generated post-second-dose antibody levels of 2,881 units per milliliter. Those who received the Pfizer-BioNTech BNT162b2 vaccine had antibody levels measuring 1,108 units per milliliter.

The study involved 1,647 fully vaccinated healthcare workers in Belgium.

Immune protection, however, involves more than antibody levels. Pfizer researchers found that recipients of their vaccine have immune protection 12 days after vaccination when there are low antibody levels, according to a STAT article.

In volunteers who had previously contracted COVID-19, the Moderna vaccine recipients generated antibody levels of 3,836 units per milliliter, while antibody levels in Pfizer-BioNTech vaccine recipients were 1,444 units per milliliter.

Some 688 volunteers received the Moderna vaccine. A total of 959 got the Pfizer-BioNTech vaccine.

The higher antibody levels in Moderna recipients could have resulted from the longer window between doses (28 vs. 21 days) or the larger quantity of mRNA in the Moderna vaccine (100 µg in the Moderna vaccine versus 30 µg in the Pfizer).

Researchers performed serologic testing six to ten weeks after receipt of the second dose of the vaccine.

The study was carried out from April 27 to May 20 — long before the rise of the Delta variant.

The mean age of recipients of the mRNA-1273 vaccine was 43.2 years old. BNT162b2 recipients skewed slightly older with a median age of 44.7.

A separate preprint study also found that the Moderna vaccine appeared to be more effective than the BNT162b2 against the Delta variant.