Antibodies Persist Through 6-Months Following 2 doses of Moderna COVID-19 Vaccine

A correspondence published in the New England Journal of Medicine today reports on findings which suggest that 2 doses of the Moderna mRNA-1273 vaccine elicited antibodies for COVID-19 which persist through 6 months.

The study, a phase 1 trial analyzing mRNA-1273-elicited binding and neutralizing antibodies at 180 days after the second dose of 100 μg, has included 33 healthy adult participants who have been stratified according to their age.

Findings from the study demonstrated that antibody activity in all of the participants remained high at day 209. In the participants aged 18-55, binding antibodies had geometric mean end-point titers of 92,451. In those aged 56-70, end-point titer levels were 62,424 and in the 71+ age group, titer levels were 49,373.

A majority of the participants had detectable activity in a pseudovirus neutralization assay, with 50% inhibitory dilution (ID50) GMTs of 80, 57 and 59, respectively.

Additionally, all of the participants had detectable activity on the live-virus focus-reduction neutralization mNeonGreen test, with ID50 GMTs of 406, 171, and 131, respectively. The GMTs in this test were seen to be lower in the older age groups than in the 18-55 cohort.

Binding antibody half-life was estimated to be 52 days for all participants after day 43 using an exponential decay model, and 109 days using a power-law model.

“Although the antibody titers and assays that best correlate with vaccine efficacy are not currently known, antibodies that were elicited by mRNA-1273 persisted through 6 months after the second dose, as detected by three distinct serologic assays,” the authors wrote. “Ongoing studies are monitoring immune responses beyond 6 months as well as determining the effect of a booster dose to extend the duration and breadth of activity against emerging viral variants. Our data show antibody persistence and thus support the use of this vaccine in addressing the Covid-19 pandemic”