Real-world effectiveness of COVID-19 vaccines: A retrospective cohort study of vaccinated individuals in Jazan, Saudi Arabia

BACKGROUND: COVID-19 (Coronavirus Disease 2019) vaccinations are a critical control measure for the coronavirus pandemic that began in 2019. Several COVID-19 vaccines have been developed, and their effectiveness will almost certainly vary. OBJECTIVE: This study aimed to assess how effective two doses of the Pfizer and Oxford-AstraZeneca vaccines were in preventing SARS‐CoV‐2 infection six months after administration. METHODS: This is a retrospective cohort study of adult individuals from the Jazan Region of Saudi Arabia who received their second dose of the COVID-19 vaccine [Pfizer and Oxford-AstraZeneca (ASZ)] between April and June 2021. The monitoring and follow-up period continued until the end of January 2022. Data were retrieved from the Health Electronic Surveillance Network and National Vaccination Records. Logistic regression was performed to assess the risk of COVID-19 infection among the vaccinated subjects. RESULTS: This study included randomly enrolled 4458 participants in Jazan who received two doses of the COVID-19 vaccine during the research period. The majority of them received the Pfizer vaccine (3136/4458; 70.3%), while the remaining received the ASZ vaccine (1322/4458; 29.7%). The study participants’ mean age was 59.7 years, with a male-to-female ratio of 1.9:1.0 (2920:1538). The results showed that the Pfizer and ASZ vaccines’ protection against infection decreased from 93.2% and 90.2%, respectively, during the first three months, to 68.5% and 68.1% after a six-month interval. In the current study population, being Saudi Arabian, younger as well as having longer intervals between vaccines or crossing a 6-month period after the second vaccine dose were factors linked to higher rates of breakthrough infections. CONCLUSION: Our findings revealed variations in the efficacy of different COVID-19 vaccine types against COVID-19 breakthrough infections. The Pfizer (mRNA-based) vaccine was found to be relatively more effective than the ASZ (DNA-based) vaccine.