A sub-cohort of Virus Watch participated in monthly at-home capillary blood sampling to test for antibodies to SARS-CoV-2. Anti-spike and nucleocapsid antibody titers were measured using Elecsys anti-spike and -nucleocapsid electro-chemiluminescent immunoassays.
A breakthrough infection was defined as a positive SARS-CoV-2 test in double-vaccinated individuals occurring at least 14 days after the second vaccination. First, antibody waning was estimated by comparing anti-spike antibody levels in ChAdOx1 and BNT162b2 recipients by sex, age, clinical vulnerability, and time since vaccination.
Nearly 25,000 samples from more than 9400 individuals were included in the analysis of anti-spike antibody decay; most people (5960) received a second dose of ChAdOx1, and 3490 received BNT162b2, and 2% of the cohort received different first and second doses.
The study found that anti-spike antibody levels peaked after three- or four weeks post-administration of the second dose, with the geometric mean being nine-fold higher for BNT162b2 than ChAdOx1. A substantial waning of anti-spike levels was evident after administering either vaccine. Notably, higher anti-spike levels were associated with a lower risk of vaccine breakthrough infection.
The team included 9244 subjects in the analysis of the effect of anti-spike antibody levels on SARS-CoV-2 infection risk. There was no association between second dose vaccine type and anti-spike levels. Overall, the antibody waning analysis findings suggested that ChAdOx1 recipients were at an elevated risk of breakthrough infection. This was further confirmed by the test-negative case-control analysis, which revealed that recipients of two ChAdOx1 doses had 1.64 increased odds of breakthrough infection relative to double-vaccinated BNT162b2 recipients.
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For a link to the full article please see: https://www.nature.com/articles/s41467-022-32265-5