Covid Vaccine: What The Results Of The Oxford Trial Tell Us

The first ever peer-reviewed study of a coronavirus vaccine has confirmed that the Oxford University/AstraZeneca jab that could go to millions of Brits is “safe and efficacious”.

Interim results from phase 3 trials – the final stage of a vaccine trial, where it is administered to thousands of people – were published in medical journal The Lancet on Tuesday, confirming the jab has “a good safety record and efficacy”. Previously, only the most top-line results had been published, not the underlying data.

The data have also been submitted to the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) for approval. The UK government has already ordered 100m doses of the vaccine.

These results are the first to be published in a peer-reviewed paper, meaning that the data have undergone extensive scrutiny by other scientific experts. Interim results from the Pfizer and Modern vaccines have so far been published only in press releases. 

Here’s what the results published today tell us.

The trials involved a total of 23,745 participants

Tuesday’s safety results are based on 23,745 adult participants in four trials that took place in the UK, Brazil and South Africa, monitored over a median period of 3.4 months.

The clinical efficacy results are based on 11,636 volunteers across the UK and Brazil.

All participants in the trial continue to be monitored for safety.

It has “a good safety record and efficacy”

Writing in the Lancet, researchers said the phase three trials showed the Oxford vaccine “is safe and protects against disease”.

No hospitalisations or severe disease was reported in the participants who received the vaccine, they added.

“Our findings indicate that our vaccine’s efficacy exceeds the thresholds set by health authorities and may have a potential public health impact,” said Oxford’s Professor Andrew Pollard, a lead author of the study.

“Control of the pandemic will only be achieved if the licensing, manufacturing and distribution of these vaccines can be achieved at an unprecedented scale and vaccination is rolled out to those who are vulnerable.”

It has an overall efficacy of 70.4%

This figure was reached by pooling the results from two different dosing regimens.

One month apart, one set of volunteers received two identical doses while the other received a half-dose, and then a full dose. In the first group, the efficacy was 62%. In the second, 90%.

The combined analysis from both dosing regimens resulted in an average efficacy of 70.4%.

“Following the demonstration of vaccine efficacy in many preclinical studies, we now have clear evidence of efficacy in the trial results presented in a peer-reviewed publication today,” said Professor Sarah Gilbert, professor of vaccinology at the University of Oxford.

“Now under regulatory review, we hope that this vaccine will shortly be in use to start saving lives.”

Here’s an explanation of what vaccine “efficacy” really means.

Most of the participants were young and white

Most of the participants in the earlier trials (82%) were aged 55 and under, with researchers saying older participants were only recruited later.

Out of the 11,636 people in the analysis of vaccine efficacy, only 12% were older and 83% were white. 

As a result, researchers said more detail is needed on how effective the vaccine is on older people.

This is particularly important as people aged 55 and over are particularly vulnerable to severe Covid-19.

Study author Dr Merryn Voysey, from the University of Oxford, said: “Since recruitment of older adults started later than in younger adults there has been less follow up time for these cohorts and less time to accrue Covid-19 cases. This means we have to wait longer to have sufficient data to provide good vaccine efficacy estimates in smaller subgroups.

“In future analyses, with more data included as it becomes available, we will investigate differences in key subgroups such as older adults, various ethnicities, doses, timing of booster vaccines, and we will determine which immune responses equate to protection from infection or disease.

How does it work?

The Oxford vaccine – called ChAdOx1 nCoV-19 – uses a harmless, weakened version of a common virus which causes a cold in chimpanzees.

Researchers have already used this technology to produce vaccines against a number of pathogens including flu, Zika and Middle East respiratory syndrome (Mers).

Scientists have transferred the genetic instructions for coronavirus’s specific “spike protein” – which it needs to invade cells – to the vaccine.

When the vaccine enters cells inside the body, it uses this genetic code to produce the surface spike protein of the coronavirus.

This induces an immune response, priming the immune system to attack coronavirus if it infects the body.

The virus is genetically modified so it is impossible for it to grow or cause disease in humans.