Studies to understand the duration of persistence of SARS-CoV-2 antibodies have been undertaken in India and abroad by multiple independent investigators and vaccine manufacturers and scientific evidence on it is still evolving, the Rajya Sabha was informed on 7 December.

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In a written reply to a question in the Upper House of Parliament, the Minister of State for Health said that in addition to antibodies, other immune mechanisms like cellular or T cell-based immune response and memory B cells are created because of vaccination and are responsible for protection against infection. She was responding to the question of whether the government has conducted any studies to check if there is a case of declining vaccine immunity amongst the elderly population.

Asked whether the government is considering giving booster shots to improve immunity, she said, "The National Technical Advisory Group on Immunization (NTAGI) and the National Expert Group on Vaccine Administration for COVID-19 (NEGVAC) are deliberating and considering scientific evidence related to dose schedule of COVID-19 vaccines and the need for a booster dose." Adequate doses to vaccinate all eligible first dose and due second dose beneficiaries aged 18 years and above by December 2021 have been made available to states and union territories, she said.