Effectiveness of COVID-19 vaccines on hospitalization and death in Guilan, Iran: a test-negative case-control study

•Sinopharm was most effective at 56% against death 4 months after receiving two doses.•AstraZeneca was most effective, up to 90% against death 5 months after receiving two doses.•COVIran Barekat was most effective against death at 90% 4 months after receiving two doses.•Sputnik V was most effective against death and was up 90% 6 months after receiving two doses. The present study was conducted to estimate the effectiveness of (BBIBP)-CorV (Sinopharm), ChAdOx1-S/nCoV-19 (AZD1222, Oxford-AstraZeneca), rAd26-rAd5 (Gam-COVID-Vac, Sputnik V), and BIV1-CovIran (COVIran Barekat) and BBV152 COVAXIN (Bharat Biotech) vaccines against hospitalization and death of COVID-19 in Guilan Province of Iran from May 22 to December 21, 2021. This test-negative case-control study was conducted on the population aged 5 years and above by extracting information from local databases (The Medical Care Monitoring Center and The Integrated Health System). A logistic regression analysis was performed to estimate the effectiveness of the vaccines against COVID-19 hospitalization and death. The total study population was 42,084, including 19,500 cases (with a positive Reverse Transcriptase-Polymerase Chain Reaction test admitted to hospitals in Guilan Province) and 22,586 controls (with a negative Reverse Transcriptase-Polymerase Chain Reaction test). Among the admitted patients, 1887 deaths occurred. The maximum effectiveness of BBIBP-CorV (Sinopharm) in preventing temporary hospitalization and regular hospitalization was observed 151 days after receiving the second dose, 95% (95% CI: 67-99.4%) and 85% (95% CI: 77-91%) respectively. The maximum effectiveness of the BBIBP-CorV (Sinopharm) vaccine 91-120 days after receiving the second dose against death was showed 56% (95% CI: 33-71%). The maximum effectiveness of ChAdOx1-S/nCoV-19 (AZD1222, Oxford-AstraZeneca) and BIV1-CovIran (COVIran Barekat) in preventing regular hospitalization and death was observed 121-150 and 61-90 days (respectively) after receiving the second dose, reaching 98% (95% CI: 94-99%) and 92% (95% CI: 48-99%), respectively for ChAdOx1-S/nCoV-19 and 95% (95% CI: 91-97%) and 89% (95% CI: 55-98%) respectively, for BIV1-CovIran. For almost all vaccines, the study observed an increase in effectiveness against hospitalization and death over time.