The Astrazeneca initial trials of various COVID-19 vaccines were large, but they took place before the Delta variant had emerged.

Now that millions of people globally have been vaccinated, we have learned about how AstraZeneca’s jab performs in a world where Delta is the predominant strain, Nick Wood from the National Centre for Immunisation Research and Surveillance said.

“What we know now is that … two doses of the AstraZeneca or the Pfizer vaccine will give you very good protection against the severe disease, like hospitalisation or even death,” Dr Wood said.

“Even a single dose would give you some good protection against the Delta strain.”

This understanding of how the vaccines perform is mostly based on data that has recently come from the UK and Canada.

Two doses of the AstraZeneca vaccine was about 92 per cent effective against hospitalisation from the Delta variant, a Public Health England analysis of about 14,000 cases found.

That’s comparable with the 95 per cent effectiveness against hospitalisation offered by the Pfizer jab.

A recent study from Canada, which is yet to be peer-reviewed, found even just one dose of AstraZeneca’s vaccine was about 88 per cent effective against hospitalisation or death from the Delta variant.

AstraZeneca  jab does help reduce the risk of transmission

Neither the AstraZeneca nor Pfizer vaccines totally eliminated the risk of catching COVID, passing it on, or developing mild illness — but they do reduce the risk, Professor Baxter said. A person who becomes infected after being vaccinated is half as likely to pass the virus on to the people they lived with.

Data from the UK shows both AstraZenecca and Pfizer vaccines stop about 80pc of infections.

The current situation in England is a good example of this. Cases have gone up, even among people who have been vaccinated, but hospitalisation rates are nowhere near the levels seen pre-vaccination.

That’s also a point made by Tony Kelleher, a clinician scientist and director of the medical research organisation The Kirby Institute.

“If you define its efficacy against preventing people getting sick enough to go to hospital, it is as effective as any of the other vaccines,” Professor Kelleher said