COVID-19 Antibodies Rapidly Decline 6 Months After Vaccination

Antibodies attacking coronavirus particle
Antibodies attacking a coronavirus particle, illustration.
Researchers assessed antibody responses among health care workers 9 months after COVID-19 vaccination.

Results of a longitudinal study confirmed that anti-receptor binding domain (RBD) antibodies conferred by COVID-19 mRNA vaccination decrease over time. In addition, women were more likely to produce antibodies at months 1 and 9 following COVID-19 vaccination compared with men. These findings were published in the International Journal of Infectious Diseases.

Researchers quantified the production of immunoglobulin (Ig) G antibodies among a cohort of 1343 health care workers who received 2-doses of the Pfizer-BioNTech COVID-19 (BNT162b2) vaccine between February and October 2021. The SARS-CoV-2 IgG II Quant assay by Abbott Laboratories (North Chicago, IL) was used to quantify antibodies at 1-, 6- and 9-months after receipt of the vaccine.

The cohort comprised 402 (29.9%) men and 941 (70.1%) women with a median age of 51 (range, 24-68) years. The median concentration of anti-RBD IgG was most increased 1 month after vaccination (1432 binding antibody units [BAU]/mL; range, 0.1-11,360 BAU/mL). At months 6 and 9, the median concentration of anti-RBD IgG antibodies among the participants decreased to 194.3 and 79.3 BAU/mL, respectively. There were significant differences between median anti-RBD IgG concentrations observed at all 3 timepoints (P <.0001), as well as between men and women at months 1 (P =.0373) and 9 (P =.0291). After stratification of participants by age and sex, no significant difference in the mean concentration of antibodies was noted at month 6.

The researchers noted the need for additional studies to clarify the ways in which patient sex affects the cellular and molecular pathways associated with COVID-19 infection.

According to the researchers, “…these data support the importance of [additional]… vaccine doses, considering also the recent findings that underscore the importance of receiving a third vaccine dose to prevent moderate and severe COVID-19, especially when the Omicron variant is predominant and the effectiveness of [2] doses of [the] vaccine is reduced against this variant.”


Bordi L, Sberna  G, Piscioneri CN, et al. Longitudinal dynamics of SARS-CoV-2 anti-receptor binding domain IgG antibodies in a wide population of health care workers after BNT162b2 vaccination. Int J Infect Dis. Published online May 31, 2022. doi: 10.1016/j.ijid.2022.05.061

This article originally appeared on Infectious Disease Advisor