Estimated COVID-19 vaccine effectiveness against seroconversion from SARS-CoV-2 Infection, March-October, 2021.

Area of Science:

• Immunology
• Public Health
• Infectious Diseases

Background:

• Ongoing monitoring of COVID-19 vaccine effectiveness (VE) against SARS-CoV-2 infection is essential for public health.
• Estimating VE using serological evidence of infection offers an alternative measure of vaccination benefits.

Purpose of the Study:

• To estimate mRNA COVID-19 vaccine effectiveness against SARS-CoV-2 infection using serological markers.
• To assess VE during the predominance of the Delta variant in the United States.

Main Methods:

• A case-control study design was employed using data from March-October 2021.
• Participants' vaccination history was collected via electronic surveys, and blood samples were analyzed for antibodies.
• SARS-CoV-2 infection was identified by the detection of new anti-nucleocapsid antibodies.

Main Results:

• Estimated VE against SARS-CoV-2 infection seroconversion was 88.8% after any mRNA vaccine (BioNTech: 87.8%, Moderna: 91.7%).
• VE was lower beyond 3 months post-vaccination and in older individuals or those with underlying health conditions.
• VE estimates using antibody detection aligned with previous studies using virologic confirmation.

Conclusions:

• mRNA COVID-19 vaccines provide substantial protection against SARS-CoV-2 infection.
• Findings support recommendations for individuals to stay up-to-date with COVID-19 vaccinations.