Moderna vaccine generates twice as many antibodies as Pfizer: study

Pfizer and Moderna vaccines
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People who are fully vaccinated with Moderna's two-dose COVID-19 vaccine may have significantly higher amounts of antibodies than those who received the Pfizer vaccine.

A study published Monday in the Journal of the American Medical Association indicates that the Moderna vaccine generates more than double the antibodies of Pfizer's vaccine.

Researchers compared the antibody levels of 1,647 health care workers at a Belgium hospital system to reach their conclusion. A total of 688 received Moderna's vaccine and 959 received Pfizer's vaccine. Testing was performed prior to vaccination as well as six to 10 weeks after the second dose.

The study found that on average, those vaccinated with the Moderna shot had antibody levels of 3,836 units per milliliter, versus 1,444 units per milliliter for those vaccinated with the Pfizer shot.

The researchers broke the data down even further to separate participants who were previously infected with the coronavirus from those who had never been infected. In both groups, they found that those who received the Moderna vaccine had higher antibody levels than those who received the Pfizer vaccine.

For participants who were previously uninfected prior to vaccination, antibody levels averaged 2,881 units per milliliter for individuals who got the Moderna vaccine compared to 1,108 units per milliliter for those who got the Pfizer vaccine.

For participants who were previously infected before getting vaccinated, antibody levels averaged 10,708 units per milliliter for individuals who got the Moderna vaccine compared to 8,174 units per milliliter for those who got the Pfizer vaccine.

As for why the Moderna vaccine seems to cause higher antibody levels compared to the Pfizer vaccine in infected as well as uninfected participants, and across age categories, the study offered two explanations.

One possibility is that the Moderna formula has a higher mRNA content -- the key active ingredient in both vaccines -- than Pfizer's formula. Another possibility is the longer interval between doses of the vaccine. Recipients are advised to wait four weeks between doses of Moderna's vaccine, versus three weeks between doses of Pfizer's vaccine.

The researchers point out that the study has limitations, including whether the observed difference in antibody levels translates to a difference in the duration of protection. The study says further research should be explored.