Those who have weaker immunity or are on a medicine that affects their immune system and people with allergies must not take the Covaxin shot, vaccine-makers Bharat Biotech warned on Monday in a fact-sheet, two days after India began mass vaccinations against Covid.Earlier, the government had said that patients who are on immuno-suppressants or suffer from immune deficiency could take the vaccine but the response would be less effective in such individuals. Usually, cancer patients who are on chemotherapy, HIV-positive people and those who are on steroids are immune-suppressed.