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Jab study Oxford Covid-19 vaccine is 'safe and up to 90pc effective', latest trial results reveal

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The UK has ordered 100 million doses of the Oxford/AstraZeneca vaccine (John Cairns/University of Oxford/PA)

The UK has ordered 100 million doses of the Oxford/AstraZeneca vaccine (John Cairns/University of Oxford/PA)

The UK has ordered 100 million doses of the Oxford/AstraZeneca vaccine (John Cairns/University of Oxford/PA)

NEW interim results of the Oxford Covid-19 vaccine trials state that the jab is safe and up to 90pc effective, depending on how it is administered.

It is stated to be effective against Covid-19 symptomatic disease in 70pc of cases – with vaccine efficacy of 62pc for those given two full doses, and of 90pc in those who received a half dose and then a full dose.

The results, published in The Lancet this afternoon, are the first full peer-reviewed efficacy results to be published for a Covid-19 vaccine.

It comes as the roll-out of the Pfizer BioNTech vaccine got under way in Northern Ireland and mainland UK this morning.

Ireland has an advance purchase agreement to buy 3.3 million of the Oxford vaccine, which is produced with AstraZeneca. It has yet to be submitted for regulatory approval.

Today’s results say the vaccine was found to be safe, with only three out of 23,745 participants, over a median of 3.4 months, experiencing serious adverse events that were possibly related to a vaccine.

All participants have recovered or are recovering, and remain in the trial.

Study author, Dr Merryn Voysey, University of Oxford, said: “The results presented in this report provide the key findings from our first interim analysis. 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.”

Study lead author, Professor Andrew Pollard, University of Oxford, says: “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.

"Our findings indicate that our vaccine’s efficacy exceeds the thresholds set by health authorities and may have a potential public health impact.”

The Oxford Covid-19 vaccine uses a chimpanzee adenovirus viral vector that cannot cause disease in humans and expresses the SARS-CoV-2 spike protein.

This means the vaccine delivers the spike protein genetic code into vaccinated people’s cells, which then produce the protein, and teaches the immune system to recognise and attack the virus. Past trial results have found that the vaccine induces antibody and T cell immune responses, and is safe in adults aged 18 years and over, including older adults .

For the new study, the authors analysed data from 23,745 adults in the UK, Brazil and South Africa (11,730, 10,002, and 2,013 in each country, respectively).

The interim analysis published today pools the data from these for analysis, providing greater precision for efficacy and safety outcomes than possible in individual trials and giving a broader understanding of the use of the vaccine in different populations

In the trial, half of the participants were given the Covid-19 vaccine and the other half given a control – either a meningococcal conjugate vaccine or saline .

The trial was originally designed to assess a single dose of the vaccine, but a review of the immune response data in the UK phase 1/2 study found a second dose boosted immune response.

Another dose was added to the trial protocol and then, once approved, second doses were given to participants.

Participants in the Covid-19 vaccine group received two doses each containing a standard dose.

However, a subset (1,367 people) in the UK received a half dose as their first dose, followed by a full second dose. This was because of differences in the results of quantification methods between batches of the vaccine.

The low-dose/standard-dose group did not include adults over the age of 55 years as the low dose was given in an early stage of the trial before recruitment of older adults had commenced.

The authors used the numbers of cases of symptomatic and asymptomatic infection to determine vaccine efficacy.

Overall, most participants were aged 18-55 years as people aged 56 years and older were recruited later and will be studied in future analyses of the trial.

In the 11,636 people included in the vaccine efficacy against symptomatic disease analysis, 12pc were older adults and most were white .

Safety was monitored for a median of 3.4 months in all 23,745 participants from the UK, Brazil and South Africa. Out of 23,745 participants, 168 experienced a total of 175 severe adverse events over the period, but 172 events were unrelated to the Covid-19 or control vaccines.

One event was in the control group (a case of haemolytic anaemia), one event was in the Covid-19 vaccine group (a case of transverse myelitis considered possibly related to the vaccine), and a case of severe fever was reported in South Africa in a participant who remains masked to group allocation and recovered rapidly without an alternative diagnosis and was not hospitalised.

All three participants have recovered or are recovering, and continue to be part of the trial.

The primary outcome of the study was to determine how many cases of symptomatic Covid-19 disease (confirmed by positive test, and the participant having a fever, cough, shortness of breath, or loss of smell or taste) there were in participants who had received two doses of the vaccine (with the first dose being either low or standard dose, and the second dose being standard dose), compared with controls.

Only cases that occurred 14 days after the second vaccination had been given were included (11,636 participants in the UK and Brazil trials).

There were 131 cases of symptomatic Covid-19 disease more than 14 days after the second vaccine dose in these 11,636 people. This included 0.5pc cases in the vaccine group and 1.7pc cases in the control group, which equates to a vaccine efficacy of 70%.

The authors completed exploratory subgroup analyses at the request of peer-reviewers to study the difference in efficacy against symptomatic disease in the low-dose/standard-dose group and two standard-doses group.

These were to help understand whether the difference was related to the dose or other factors (participant age and time between vaccine doses).

They found that, irrespective of age or time between doses, their analysis suggested higher efficacy in the low-dose/standard-dose group. However, these exploratory analysis provide a suggestion, and will require further research as more data becomes available from the trial.

Five cases of symptomatic Covid-19 disease occurred in people aged over 55 years, but vaccine efficacy in older age groups could not be assessed as there were too few cases. The authors say that this analysis will be completed in future.

“In order to assess vaccine efficacy, we need to have a sufficient number of Covid-19 cases among participants to indicate that the vaccine is protecting them from disease.

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.” says Dr Voysey.


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