India will soon start trials to test the safety, immunogenicity and efficacy after mixing doses of different brands of Covid-19 vaccines. While the trials will currently include Covaxin, Covishield and Sputnik-V, which currently have emergency use authorisation in the country, going forward the trials may also include jabs that are in the pipeline, senior officials said. Some studies in the UK and Spain have shown mixing of Pfizer and AstraZeneca vaccines to be safe and immunogenic. However, officials in India maintain that though the concept is scientifically feasible, it cannot be allowed without adequate evidence and therefore, a study has to be conducted. “It is scientifically possible and it is a good thing, especially in a country like ours, such a thing (mixing of doses) will really help boost the vaccination programme. But it is currently not allowed under the vaccination protocol and there is no question of allowing it to happen without adequate evidence generated through trials. Therefore, we have decided to have studies to test the same,” a senior official said. The decision has also been endorsed by the National Technical Advisory Group on Immunisation (NTAGI). The study — expected to start soon and likely to take about two months — will be conducted by the government in collaboration with vaccine manufacturers. Apart from testing the safety and feasibility of mixing doses of different vaccines, the study will also evaluate whether mixing of doses of different vaccines help boost immune response to the virus.