Background: As the global number of confirmed cases rises past 640 million, vaccination remains the most effective measure in controlling COVID-19. Studies have shown that two doses of vaccination can significantly reduce hospitalization and mortality rates among patients, but the effectiveness of booster doses is also important. We aimed to evaluate the role played by the type of the 3rd dose of vaccination by comparing the safety and efficacy of two common vaccination histories differing only in the 3rd received dose. Methods: We conducted a cross-sectional study on patients with respiratory symptoms suspected of having SARS-CoV-2 infection using Real-time PCR. We also collected information on the age, gender, and type of vaccine received for the third dose. Results: Out of 346 cases with respiratory symptoms, 120 cases tested positive for SARS-CoV-2 and had received two doses of Sinopharm and a different booster dose of either AZD1222 (AstraZeneca) or BIBP (Sinopharm). Among these 120 patients, vaccination with AZD1222 as a booster dose resulted in fewer symptoms compared to those vaccinated with three doses of BIBP. Conclusions: Our study demonstrates that booster doses can help reduce hospitalization and the severity of infection, and it appears that a combination of different vaccines may be effective against severe COVID-19 infection.
