Effectiveness of COVID-19 Vaccines: Eight Months Post Single Dose Vaccination

Objectives: To describe the real-world data on the effectiveness of Pfizer-BioNtech BNT162b2 and AstraZeneca-Oxford AZD1222 vaccines against COVID-19 in a large cohort in the Kingdom of Saudi Arabia (KSA). Methods: A total of 18,543 subjects received a single-dose of either of the vaccines at one vaccination centre in KSA, and were followed up for three to eight months. Clinical data from medical records, adverse events (AEs) from a self-reporting system, and COVID-19 infection data from the national databases were retrieved and analysed. Results: Subjects median age was 33 years old with an average of 27.3 body mass index and the majority were male (60.1%). 92.17% of the subjects had no COVID-19 infection post-vaccination. Diabetes mellitus (p=0.0325), organ transplantation (p=0.0254), and morbid obesity (p=0.0014) were risk factors for infection post-vaccination. Unlike vaccine type, being Saudi, male, or obese was more likely to get the infection earlier. AE reports from 1084 subjects included injection site pain, fatigue, fever, myalgia, headache. Conclusion: Single-dose COVID-19 vaccines in KSA showed an effectiveness rate of 92.17% up to eight months follow-up. The rate for AZD1222 was higher than what have been previously reported. Side effects and AEs were within what has been reported in clinical trials.