Significant adverse effects are "unlikely" if an individual's second Covid vaccine dose is different from the first, the centre said Thursday afternoon, in response to controversy over a group of Uttar Pradesh villagers being given mixed doses at a government hospital in Siddharthnagar district. "This should be looked into. We will have to wait for more scientific understanding... but even if two doses of two different vaccines are given, this should not be a cause of concern," Dr VK Paul, the Chair of NEGVAC (National Expert Group on Vaccine Administration for COVID-19), said.