No data yet on changing jabs between doses: WHO

The World Health Organization has called for studies on so-called mixing and matching between vaccines, but said there was no comprehensive data so far on which it could make any recommendations.

The UN health agency therefore recommends that the same product should be used for both doses.

In February, the WHO's Strategic Advisory Group of Experts on Immunization (SAGE) issued its recommendations on how the AstraZeneca-Oxford vaccine should be used, WHO spokeswoman Margaret Harris told reporters.

"There is not adequate data to be able to say whether this is something that could be done," she said.

Several clinical trials are looking at the efficacy of combining two types of vaccine.

Europe's medicines regulator said this week that the AstraZeneca vaccine could cause very rare blood clots among some recipients, prompting several countries to scale up restrictions on the jab.

France yesterday said under-55s who received a first injection of the AstraZeneca Covid-19 vaccine should be given a jab from a different producer for their second dose, in a ruling affecting 533,000 people.