Abstract
Background: Before the SARS-CoV-2 Delta variant arrived in Vietnam, case rates suggested seroprevalence of SARS-CoV-2 was low. Beginning in March 2021, we assessed different dosing schedules and adverse events following immunization (AEFIs) for ChAdOx1 nCoV-19 vaccine among healthcare workers (HCWs).
Methods: We performed a prospective cohort study to estimate the prevalence of IgG antibodies to SARS-CoV-2 before and after ChAdOx1 nCoV-19 vaccination. We conducted antibody testing among HCWs in February 2021 (baseline), before the second dose (June-July 2021), and 1 and 3 months after the second dose. We detected antibodies to SARS-CoV-2 using Tetracore® FlexImmArray™, and surrogate neutralizing antibodies using GenScript cPass™. Neither assay can distinguish natural from vaccine-induced antibodies. We assessed AEFIs through interview post-dose 1 and 1 month post-dose 2.
Results: Before vaccination, 1/617 participants (0.16%) had antibodies to SARS-CoV-2. Of these 617, 405 were vaccinated with ChAdOx1 nCoV-19 with 4-8- (60%), 9-12- (27%), or ≥13-week (13%) intervals between the 2 doses. Three months following series completion, 99% and 97% of vaccinated participants had ≥1 sample with detectable antibodies and surrogate neutralizing antibodies against SARS-CoV-2, respectively. We observed no significant differences among those with different dosing intervals at last follow-up. All participants reported PCR testing for SARS-CoV-2 during the study; 2 (0.5%) were laboratory-confirmed. AEFIs were more frequent post-dose 1 (81%) vs post-dose 2 (21%).
Conclusions: In this population, regardless of dosing interval, ChAdOx1 nCoV-19 induced antibodies within 3 months of the second dose. These findings may offer flexibility to policymakers when balancing programmatic considerations with vaccine effectiveness.
Keywords: SARS-CoV-2; seroprevalence; vaccination.
【저자키워드】 SARS-CoV-2, Seroprevalence, vaccination., 【초록키워드】 neutralizing antibody, Vaccine, Antibody testing, vaccination, antibody, prospective cohort study, delta variant, immunization, healthcare worker, Prevalence, PCR testing, IgG antibody, HCWs, adverse event, Effectiveness, Follow-up, ChAdOx1 nCoV-19, ChAdOx1 nCoV-19 vaccine, HCW, no significant difference, second dose, vaccine-induced antibodies, participant, doses, laboratory-confirmed, offer, dosing interval, Genscript, performed, detected antibody, reported, detectable, conducted, suggested, interval, All participant, baseline, cPass™, dosing schedule, the SARS-CoV-2, 【제목키워드】 coronavirus 2, respiratory, ChAdOx1 nCoV-19, Dosing, worker, interval, Presence,