No one can answer that now. My guess is that mRNA vaccines may be safest and most efficacious. Both Moderna and Pfizer vaccines are using this method. Here, vaccines make use of messenger RNA molecules to tell the body’s cell what proteins to build to fight the virus.
But, both Pfizer and Moderna are out of reach for Indians, so ‘Killed virus’ vaccines may be equally safe though efficacy needs to be measured. I expect very high efficacy, equal to mRNA vaccines. In a “killed virus” vaccine, a chemically-inactivated virus is used and it does not infect, but it retains the spike protein. Covaxin by Bharat Bio is an example of this kind of vaccine candidate. We do not have data, but I am guessing from a safety point of view, neither the mRNA vaccine, nor the killed virus vaccine will introduce alive virus into the body. Hence, likely to be quite safe. Many killed virus vaccine such as for Hepatitis A, Polio IPV, rabies, influenza have been highly successful.
Adeno-vectored vaccines such as AstraZeneca/Oxford vaccine and Sputnik V vaccine, are introducing a virus into the body. At the moment, we are unclear about safety and efficacy. Here the safety has to be documented.
DNA vaccines, such as the vaccine candidate from Zydus Cadila, may be safe but probably less efficacious than others. Many DNA vaccines have been tried, but they don’t do quite well. Efficacy has not been up to the mark. Proof of the pudding is in its eating. Let the cooking of the pudding be over.