As Bangladesh is now administering four types of Covid vaccines without joining the trial of anyone, health experts suggest conducting a comprehensive study to know their comparative performances and the longevity of antibodies they produce. They said some small studies have been conducted by different organisations in the country with insignificant sample size, mainly on the efficacy of AstraZeneca vaccine, but there is no study on other vaccines -- Pfizer, Moderna and Sinopharm. The analysts think an inclusive study will help understand which vaccine is most suitable and effective in Bangladesh as the efficacy of vaccines varies from country to country and race to race. Read India to restart Covid vaccine exports to COVAX, neighbours Besides, the analysts also said a nationwide serosurveillance also should be conducted to know how much people gained natural antibody through Covid infection and its durability as they believe a good portion of the population has already been infected with the virus.