Antibody Response to Omicron Variant Reduced 8 Months After COVID-19 Vaccination

Antibodies against Omicron BA.1 saw a reduction as time went on post vaccination, according to a study published in The Journal of Infectious Diseases. Researchers found that antibody responses to BA.2 and BA.5 were also reduced.

Omicron became the dominant variant of concern in December 2021, with 6 infectious subvariants: BA.1, BA.2, BA.3, BA.4, BA.5, and a recombinant form of BA.1/BA.2. Personnel from the Department of Defense in the United States are at a higher risk of contracting COVID-19 due to proximity in training, deployments, and operations abroad. This study aimed to assess how effective the Moderna vaccine and booster for Omicron subvariants BA.1, BA.2, and BA.5 were in active-duty personnel who were in the Indo-Pacific Command Area of Responsibility.

Participants were gathered from 4 US Navy vessels and a 3D Marine Logistics Group. A cross-sectional study of the 5 study sites occurred from February to September of 2021. All participants completed a questionnaire that included information on demographics, travel, clinical symptoms in the last 60 days, vaccination history, and current medicine. Participants also self-reported their vaccination dates.

A recombinant COVID-19 spike protein that was produced in house and a nucleocapsid protein (N protein) were used to coat ELISA plates. Microplates were coated with 2 mcg/mL of antigens for COVID-19 immunoglobin G (IgG) ELISAs. Pseudoviruses were created for the ancestral strain.

There were a total of 707 participants in this study: 49 were unvaccinated, 96 were partially vaccinated, and 562 were fully vaccinated. A total of 21.4% identified as women and had equal representation in the unvaccinated, partially vaccinated, and vaccinated groups. The median (IQR) age for the unvaccinated group was 25 (19-41) years; partially vaccinated group, 26 (19-53) years; and the unvaccinated group, 27 (19-59) years. All samples were collected between February 3 and August 13 or September 15 in 2021.

The researchers measured immunoglobin M (IgM) and IgG to N protein, where the N IgM/IgG positivity was found to be 15.8%, 36.73%, 31.25%, and 22.9% in the prepandemic panel and the unvaccinated, partially vaccinated, and fully vaccinated groups, respectively. N prevalence was higher in the unvaccinated and partially vaccinated groups compared with prepandemic levels. The fully vaccinated group had lower N prevalence than the unvaccinated group.

Antibody neutralization was performed on 306 randomly selected samples. Levels in these samples ranged from below detection to 4.472 LOG, with a decrease over time. Reduction in months 7 and 8 was 11.6 times compared with the first 60 days. Antibody responses were maintained over 8 months but reduced over time.

The neutralizing antibody response to BA.1 was tested with 126 individuals who were fully vaccinated and made up the participants whose samples were taken 1 to 230 days after their second dose. There was a significant reduction in antibody response for BA.1 for all time periods. The amount of individuals who were able to maintain an antibody response decreased from 46% during days 0 to 60 to 8% by days 181 to 240.

Limitations on these findings include that the study population was younger, with a median age of 27 years, and men comprised most of the population. T-cell data were also lacking due to peripheral blood mononuclear cells not being collected.

The researchers concluded that the 2-dose Moderna vaccine has waning neutralizing antibody response over time. The researchers suggest that additional doses of the vaccine be administered that target Omicron variants.

Reference

Sun P, Balinsky CA, Jiang L, et al. Antibody responses to the SARS-cov-2 ancestral strain and omicron variants in Moderna mrna-1273 vaccinated active-duty U.S. navy sailors and marines. J Infect Dis. Published online March 1, 2023. doi:10.1093/infdis/jiad054