The Covid-19 vaccine developed by Pfizer and BioNTech is effective at preventing symptomatic and severe disease in people with some chronic illnesses, like diabetes and heart disease, the biggest real-world study showed.

The analysis of almost 1.2 million people by Israel's largest healthcare provider will offer further hope for countries as they get shots into citizens' arms, particularly those considered vulnerable, and curb the pandemic that has killed more than 3.1m people.

The vaccine was 80 per cent effective against symptomatic infection for people with heart or chronic kidney diseases, 86pc for people with type 2 diabetes, 75pc for cerebrovascular disease, and 84pc for people suffering from immunodeficiency, according to the Clalit Research Institute study.