HelCoVac: Comparison of Different BNT162b2 and ChAdOx1-S COVID-19 Vaccination Intervals and Combinations on Reactogenicity and Humoral Immunogenicity in Adults

The basic immunizations (first and second vaccination) were performed from January to June 2021 using the m-RNA vaccine BNT162b2 (BioNTech/Pfizer, B)9 and the vector-based vaccine ChAdOx1-S (AstraZeneca, A). BNT162b2 was used to boost vaccine all study population. The time interval between the basic immunisation and the boost vaccination varied.

Four vaccine-groups could be distinguished:

Group 1 received BNT162b2 with the second vaccination 3 weeks after the first vaccination.

Vaccinees of groups 2 and 3 received AZD1222/ChAdOx1-S as first vaccination and could choose after 12 weeks whether second vaccination with BNT162b2 or AZD1222/ChAdOx1-S should be carried out. This results in homologous (first: AZD1222/ChAdOx1-S, second: AZD1222/ChAdOx1-S) and heterologous (first: AZD1222/ChAdOx1-S, second: BNT162b2) vaccine combinations.

Group 4 received BNT162b2 with the second vaccination 6 weeks after first vaccination.

Blood samples were collected at six time points: four weeks, three and six months after completion of the basic immunization, immediately before boost vaccination, four weeks and three months after boost vaccination.

Reactogenicity after first, second, and boost vaccination was assessed using questionnaires to determine vaccine-induced adverse drug reactions (ADR) within seven days after the respective vaccinations.

In addition, demographic data (age, gender, occupational group, allergies) were collected, local and systemic vaccination reactions are differentiated and the need for medication and inability to work as a result of vaccination reactions are prospectively recorded.