Rationale
Neutralizing immunity toward severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) wild type (WT) and variant viruses decreases with time after vaccination and/or infection. However, the relative rates of decrease are not known. This is important for the timing of booster vaccinations and preventing viral reinfections.
Methods
We examined a 653-subject cohort with sera collected three times at 3-to-6-month intervals from April 2020 to June 2021 before the advent of the Delta variant. Individuals were categorized according to SARS-CoV-2 infection and vaccination status. Pseudoviral neutralization was performed on all samples using HEK-293T cells infected with SARS-CoV-2-pseudotyped lentiviral particles for WT, B.1.617.2 (Delta), and B.1.1.529 (Omicron) variants. Individuals with a history of infection without any vaccination or a history of vaccination without any infection were analyzed over time. A cohort that had both infection and vaccination was also studied for comparison. Linear mixed effects models of log-transformed IC50 values analyzed the role of time since infection or vaccination.
Results
Viral neutralization titers of infected-only subjects showed no significant decrease over time for all variants, for up to 270 days after infection. Solely vaccinated individuals showed decreasing neutralization titers in the WT and Delta variants. Titers to Omicron were initially low in this vaccine group and therefore the rate of decline could not be determined.
Conclusions
Time since vaccination had a much greater impact on neutralization titers compared to time after infection. Neutralization is more durable in the setting of prior infection with or without vaccination compared to a 2-dose vaccination regimen alone.
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