"There is a good scientific basis for expecting" heterologous vaccination "to be safe and effective when applied against Covid-19."
This is what we read in the joint note released today by Ema and Ecdc.
"We are not in a position to make a definitive recommendation on the use of different vaccines for the two doses - note Ema and Ecdc - but despite this, the preliminary results of the studies conducted in Spain, Germany and the UK suggest a satisfactory immune response and no problem of safety".