An expert panel of the World Health Organization has said that it is best to administer two doses of the same COVID-19 vaccine; however, mixing and matching seems good for countries which face supply issues.

Alejandro Cravioto, the panel’s chairman, said that the best approach seems to be using the same vaccine for the two doses in the primary series. Using vaccine combinations, by mixing and matching, could be beneficial for low- and middle-income countries which are dealing with vaccine shortages amid the spread of the Omicron variant. 

Cravioto stated that if countries consider a mix of vaccines, it is best to administer a second dose of a messenger RNA or vector-based vaccine if the first jab was that of an inactivated vaccine. Messenger RNA vaccines can be followed by vector-based shots... (NDTV – Bloomberg, December 9, 2021)