Updated: January 03, 2021 12:04 IST The immune responses of people to natural infection can be modified by immune evasion mechanisms of the virus Share Article AAA Protection level: Asymptomatic infections may result in low antibody levels or even no antibodies being measured in up to 20% of people. | Photo Credit: zoranm The immune responses of people to natural infection can be modified by immune evasion mechanisms of the virus As on January 1, nearly 10.3 million SARS-CoV-2 cases have been reported in India, and in all about 50% of people in large urban cities and about 30% of those across India would have already been infected. The four high-risk groups that would receive the vaccine on priority in India alone amount to 300 million people, meaning 600 million doses would be required to vaccinate them.