Scientists have not yet revealed whether different mRNA jabs would cause a conflicting bodily response.
But they remain dedicated to producing as many different types as possible, given potential differences in cost and effect.
For example, the Pfizer and Moderna jabs provide 95 percent protection but require storage in specialised refrigerators.
The Oxford vaccine, which is faintly less effective than its American cousins, costs less and needs storage only in a traditional fridge.