• Ahlam Alghamdi, Nasser Alsanea, Mohammed Alraey, Mercy Joseph, Mohammed Aboud, Thamer Almangour, Wasaef Alharbi, Hind Alhumidan, Abdalrhman Alanizi, and Ahmed Al-Jedai.
• From the Department of Pharmacy Practice, College of Pharmacy, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.
• Ann Saudi Med. 2022 Jul 1; 42 (4): 223-228.

BackgroundThe 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.ObjectivesAssess 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.DesignCross-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 MeasuresThe rate of SARS-CoV-2 infection within 16 weeks post-vaccination.Sample Size385 participants with median (IQR) age of 34 (29-38) years.ResultsEleven (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%.ConclusionA 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.LimitationsSmall sample size and single-center.Conflict Of InterestNone.

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