Janssen single dose Covid vaccine is 66% effective - is it enough protection?

The Janssen developed Covid vaccine is 66 per cent effective and can be fully administered through just one dose, the Belgian company has announced.

The UK has already pre-ordered 30 million doses of the vaccine.

The announcement comes after Novavax revealed its Covid-19 jab was 89 per cent effective from one dose.

A vaccine’s efficacy is estimated by comparing the numbers of new cases in vaccinated and unvaccinated people. This is normally done through a randomised control trial, which sees volunteers receive an injection. At random, volunteers receive either the actual vaccine or a placebo jab, not knowing which they are getting.

A 66 per cent efficacy means a 66 per cent reduction in new cases of the disease in the vaccine group, compared with the placebo group.

Both vaccines will need to be reviewed by regulators before they can be distributed for immunisations.