Assessing the Effectiveness of COVID-19 Vaccines in Pakistan: A Test-Negative Case-Control Study

Background: There is a dearth of data on real world effectiveness of COVID-19 vaccines outside of a clinical trial setting in developing countries. In Pakistan, inactivated vaccines were first introduced in February 2021 as part of the national vaccination efforts. Later, mRNA and viral vector vaccines were added to the program.Methods: We used a test negative case control design to describe the effectiveness of various COVID-19 vaccines in Pakistan. Adult residents of Karachi tested for COVID-19 using RT-PCR at the Aga Khan University Hospital testing facility between June-September 2021 were contacted via phone calls. People who were symptomatic within a week prior to the test and provided verbal consent were enrolled in the study. Detailed information was collected on exposure, symptom history and vaccination status. Individuals who were positive on PCR were classified as cases and those negatives were classified as controls. Effectiveness of different vaccines were calculated by comparing vaccination rates between cases and controls after adjusting for known confounders.Findings: In total, 1597 cases and 1590 controls were enrolled. Among cases, 38·1% were fully vaccinated and 53·3% among controls were fully vaccinated. Sinopharm was the most used vaccine (61·6%) followed by Sinovac (25·6%) with adjusted vaccine effectiveness estimates of 33·8% (95% CI:18·6% - 46·1%) and 49·3% (95% CI: 34·8% - 60·6%) respectively. The highest vaccine effectiveness estimate was for the mRNA vaccines at 67·4% (95% CI: 1·8-89·2%).Interpretation: We report inactivated COVID-19 vaccines were moderately effective against symptomatic infection in adult Pakistani population. The mRNA vaccines had higher effectiveness comparable to that observed in other parts of the world.Funding Information: This study was funded by the Infectious Diseases Research Laboratory (IDRL) at the Aga Khan University.Declaration of Interests: All authors declare no conflict of interest.Ethics Approval Statement: Ethical approval was obtained from the Aga Khan University’s Ethics Review Committee (AKU ERC).