To ensure that a vaccine is safe, we need to try it on a large number of people. The vaccine developers have not reduced the sample size at any stage of clinical trials rather it was bigger than what we usually test a vaccine on.

When a vaccine is tested, most of the adverse events or unwanted effects, if any, occur in the first four to six weeks of its administration. So, in order to ensure that it is safe, we keep a close watch, for the first two-three months, on the people it has been given to. This data help us decide if a vaccine is safe. All concerned in the line of vaccine development, testing and evaluation have followed these procedures to the T. Both Indian vaccines are considered safe on this yardstick.

As for the efficacy of the vaccine, we need time to tell how effective a vaccine is. All the global agencies have set the benchmark that only those vaccine candidates which show an efficacy of at least 50-60% will be considered. Most of the vaccines have shown an efficacy of 70-90% within the short period of two to three months of observation. Besides when a vaccine is given an emergency use authorizations/permission for restricted use, as in the case of the COVID-19 vaccine, the trial follow-up continues for one-two years to assess the total duration of protection the vaccine will provide.

Longevity of the immune response in vaccinated individuals is yet to be determined. Hence, continuing the use of masks, handwashing, physical distancing and other COVID-19 appropriate behaviours is strongly recommended.

Both the vaccines are safe but in case of any discomfort or complaint, ask the beneficiary to visit the nearest health facility and/or call the health worker whose phone number is given in the Co-WIN SMS received after vaccination.

As per experts, there is no evidence of alcohol impairing the effectiveness of the vaccine.

COVID-19 affects all age groups; however, morbidity & mortality is several times higher in adults particularly in those above the age of 50 years. Children have either asymptomatic or mild infection. The general practice is to first evaluate any new vaccine in older population and then age reduction is done to assess the safety and effectiveness in paediatric population. The currently available vaccines have not been evaluated in children so far. There are some clinical trials now underway to test the effectiveness and safety of the COVID-19 vaccines in children.

When an increasing number of people get vaccinated in the community, indirect protection through herd immunity develops. The percentage of people who need to be immune in order to achieve herd immunity varies with each disease. For example, its 95% for measles, however the proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity is not known.

Chronic diseases and morbidities like the cardiac, neurological, pulmonary, metabolic, renal and malignancies etc. are not contraindicated. In fact, the benefit of COVID-19 vaccines to reduce the risk of severe COVID-19 disease and death is for those who have these comorbidities.