Vaccine scarcity has prompted researchers and public health officials to examine strategies such as mixing two different shots.

Mixing of doses of COVID vaccines resulted in side effects such as fatigue and headaches.

According to the researchers from the University of Oxford, a first dose of AstraZeneca's vaccine followed by Pfizer's vaccine four weeks later showed short-lived side effects.

Trials are going on to ascertain whether the mixing of vaccines could benefit patients.

In India doctors are advising not to mix vaccines.