Pfizer’s jab relies on a live piece of genetic code which must be kept at -70C, making it less convenient and more expensive than Oxford’s traditional vaccine. 

Pfizer Inc and German partner BioNTech SE had produced over 70 million doses of their Covid-19 vaccine by the end of 2020. Overall, the UK has ordered 40 million doses.

BioNTech said on Jan 11 the companies were raising the 2021 delivery target for their Covid-19 vaccine to 2 billion doses, up from 1.3 billion, as they add new production lines and as more doses can be extracted per vial.

Though, deliveries of the Pfizer vaccine to the UK will be cut by between 15 and 20 per cent from Jan 25, due to delays in shipments because of work to increase capacity at its Belgian processing plant, sources said.

Why is there a delay between the first and second Pfizer jabs?

The decision to widen the gap between the doses has faced criticism from GPs and scientists, after some elderly and vulnerable people were told they would have to wait longer for their second jabs.

Regulators had previously said that two doses should be administered between four and 12 weeks apart. 

However, Professor Chris Whitty said that extending the gap between the first and second jabs would mean the number of people vaccinated could be doubled over three months.

“If over that period there is more than 50 per cent protection, then you have actually won. More people will have been protected than would have been otherwise,” he told a No 10 news conference.

“Our quite strong view is that protection is likely to be a lot more than 50 per cent.”

However, on Jan 20 the UK’s chief scientific adviser said the UK will have to look “very carefully” at the effectiveness of a single dose of the Pfizer/BioNTech coronavirus vaccine,  after reports from Israel suggested the protection it provides may be much lower than shown in trials.

Responding to Israel’s claims that efficacy from the first dose of the Pfizer vaccine may be as low as 33 per cent, Sir Patrick Vallance said studies showed that from day 10 after vaccination to 21 days and beyond, it was “much more like 89 per cent”.

Meanwhile, Professor Anthony Harnden, deputy chair of the JCVI, said they are advising people should have a second dose of another vaccine, rather than no second dose, if supply issues make it impossible to have two doses of the same medicine.

He told BBC Breakfast on Jan 29: “The key thing at the moment from the JCVI perspective is to try and get the same vaccine for the second dose as the first dose.

“We are recommending a second dose because that’s important for long-term protection and it will be interesting to see on the supply side whether we can deliver that.

“If we can’t deliver that, JCVI advice is that it’s better to have a second dose of a different vaccine than no second dose at all, and there’s no theoretical reason why you can’t mix vaccines, just the studies are ongoing at the moment.”

What’s the latest on Oxford’s AstraZeneca vaccine? 

The Oxford vaccine was approved by the Medicines and Healthcare products Regulatory Agency on Dec 30 and started to be rolled out from Jan 4.

Brian Pinker, 82, was the first person to be administered with the vaccine, at Oxford University Hospitals NHS Foundation Trust’s Churchill Hospital.

He said: “I am so pleased to be getting the Covid vaccine today and really proud that it is one that was invented in Oxford”.