Safety, Tolerability and Immunogenicity of Oxford-AstraZeneca ChAdOx1 Vaccine Among Polish School-Teachers

Background: Polish teachers, as the priority group, were offered the ChAdOx1-S vaccine since February 2021. The objective was to investigate safety, tolerability and immunogenicity of this vaccine following two vaccine doses. Methods Teachers were invited for serological testing ≥8 weeks after second vaccination. Quantitative post-vaccination anti-spike antibody responses were measured using the Abbott SARS-CoV-2 IgG II Quant assay (detection threshold: ≥7.1 BAU/ml). Multivariable logistic regression methods were used to identify predictors of immunogenicity. Results Of 192 teachers, mean age 50.5±8.3 years, 83.9% were females. Median (range) dosing interval was 50 (14-95) days; median interval between the second dose and immunogenicity test was 69 days (range: 57–111). More than a half of teachers (58.3%) reported they would change the product for another (mostly mRNA) vaccine if there was such an opportunity. Adverse reactions after receiving the vaccine (either the first or the second dose) were reported by 79.2% teachers, more frequently after the first dose (84.9%), and were similar in nature to those previously reported: feeling feverish (44.8%), headache (41.7%), malaise, chills (both: 38.0%), injection-site tenderness (37.5%) and pain (32.3%). Less males than females (54.8% vs 80.1%) and older (aged ≥50 years) than younger teachers (65.7% vs 90.4%) reported side effects (p<0.002; p<0.0001, respectively). By ≥8 weeks after the boost dose, all teachers had neutralizing antibody responses. The median (range) anti-spike IgG reading was 525.0 BAU/mL (20.6-5680.0 BAU/mL); 1008.02 (115.3–5680.0) BAU/mL in teachers with evidence of prior infection and 381.42 BAU/mL (20.6–3108.8) in those without (p=0.001). Previous infection with SARS-CoV-2 and longer dose interval were both positive predictors of higher immunologic response (p<0.0001; p=0.01, respectively), with no evidence of differences by age, gender, BMI, smoking or comorbidities. Conclusions The results demonstrated good safety, tolerability and immunogenicity of the ChAdOx1-S vaccine. Immunization led to detectable anti-spike antibodies in all teachers. Our study justifies the longer dose interval as an important factor to enhance higher antibody response. Findings suggest that in immunocompetent vaccine recipients with an evidence of previous infection a delay regarding the second dose could be considered when careful management in the use of vaccine resources is needed.