Outcome after single dose of ChAdOx1 vaccine against SARS-CoV-2 infection at 16 weeks post-vaccination among healthy adults in Saudi Arabia

BACKGROUND:
The rate of severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) infection and immunogenicity of a single dose of ChAdOx1 vaccine at 16 weeks post-vaccination among young and healthy participants remains unclear in Saudi Arabia.


OBJECTIVES:
Assess the rate of subsequent infection and immunogenicity of a single dose of ChAdOx1 vaccine at 16 weeks post-vaccination in a sample of healthy and young participants.


DESIGN:
Cross-sectional study


SETTING:
Academic teaching hospital in Riyadh, Saudi Arabia


SUBJECTS AND METHODS:
Healthy participants 18–50 years of age, who received one dose of ChAdOx1 vaccine and had no history of SARS CoV-2 infection were recruited, and blood samples were obtained 16 weeks after vaccination to assess immunogenicity using a commercially available kit.


MAIN OUTCOME MEASURES:
The rate of SARS-CoV-2 infection within 16 weeks post-vaccination.


SAMPLE SIZE:
385 participants with median (IQR) age of 34 (29-38) years.


RESULTS:

Eleven (2.8%) participants acquired polymerase chain reaction (PCR)-confirmed infection within 16 weeks after a single dose of ChAdOx1 vaccine (mean [SD] 42.5 [28] days post-vaccination). No hospital or intensive care unit admissions occurred among the subjects in this sample. Females were significantly over-represented in PCR-confirmed cases of SARS-CoV-2 infection, with 10 of 11 infections occurring in females (
P
=.006). Antibody response against anti-spike IgG were detectable in 92.7% of subjects at 16 weeks’ post-vaccination. The median anti-spike IgG level after vaccination was 273.1 (IQR 107-1052 AU/mL). However, the anti-nucleocapsid IgG antibody demonstrated a sensitivity of only 20%.



CONCLUSION:
A single dose of ChAdOx1 vaccine in healthy and young individuals was associated with a low, single-digit rate of PCR-confirmed infection, most of which were mild.


LIMITATIONS:
Small sample size and single-center.


CONFLICT OF INTEREST:
None.