'Full-proof' study needed before choosing Covid vaccine: Mamata tells PM Modi in meeting over vaccine rollout West Bengal CM Mamata Banerjee submitted that optimal number of trials and "full-proof" studies through such trials were needed before vaccinations were unequivocally advised in favour of both the vaccines. The Bengal chief minister also requested the Union government to clarify whether there might be any side effects, post vaccination. advertisement West Bengal CM Mamata Banerjee. (File photo: PTI) West Bengal Chief Minister Mamata Banerjee on Monday stressed on the need for obtaining adequate scientific opinion before confirming the safety and efficacy of both the vaccines chosen by the Government of India in the fight against Covid-19.