Watch: Oxford Covid-19 vaccine has good safety record and efficacy, according to study
A late-stage study into the University of Oxford-AstraZeneca’s coronavirus vaccine has suggested the candidate protects against severe disease.
Interim results were met with both enthusiasm and scepticism after the team reported the jab was 70% effective at warding off the infection.
Surprisingly, the two-dose regimen was reported to have up to 90% efficacy when the first vaccine was given at a half dose, followed by a full dose 28 days later. When both jabs were full dose, efficacy was reported at 62%.
Many experts were perplexed that the 62% and 90% figures were pooled to create an overall efficacy outcome of 70%, despite different doses being administered to achieve these percentages.
Nevertheless, a full read-out of the preliminary results from the ongoing study has confirmed the above findings. This may be sufficient for approval given vaccine regulators set the efficacy threshold for a coronavirus jab at 50%.
The results have also revealed no cases of hospitalisation or severe disease have arisen to date among those receiving any dose regimen of the jab, according to data published in the prestigious medical journal The Lancet.
This is the first time complete efficacy findings for a coronavirus vaccine candidate have appeared in a peer-reviewed paper, despite the approved Pfizer-BioNTech jab already being rolled out to care home residents and staff in the UK.
Stressing the importance of “transparency”, the scientists have submitted their results to vaccine regulators around the world, including the Medicines and Healthcare products Regulatory Agency, the UK-approval body.
“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,” said lead author Professor Andrew Pollard.
“Our findings indicate our vaccine’s efficacy exceeds the thresholds set by health authorities and may have a potential public health impact.”
The government has pre-ordered millions of doses of different coronavirus vaccines, including Pfizer’s, the Oxford-AstraZeneca collaboration’s and a fellow front-runner from Moderna, which is also yet to be approved.
Variations in how the different vaccines were developed means the Oxford-AstraZeneca candidate can be stored in a domestic fridge, while the Pfizer and Moderna jabs require temperatures of around -80C (-112F) and -20C (-4F), respectively.
Many have flagged this as being a logistical set back for the Pfizer and Moderna vaccines, particularly when it comes to immunising rural residents in less developed countries.
Watch: Can you catch coronavirus twice?
Critics previously accused the Oxford-AstraZeneca team of muddled dosing, after it emerged some of the participants received an initial half dose of the jab, despite two full doses being listed on the trial’s protocol.
It later came to light some of the vaccine vials used in the trial did not contain the full concentration of the jab due to a manufacturing error, which was only identified when some of the participants experienced milder side effects than expected.
The Oxford-AstraZeneca team claim they discussed the dosing error with vaccine regulators, who gave the green light for some of the participants to receive one half dose and the remainder to have two full doses as planned.
A pooled analysis, which led to the 70% efficacy outcome, was also agreed with regulators.
When asked whether the pooled result will affect approval, Professor Pollard said: “It is entirely up to the regulators to look at the data.”
The efficacy results are based on trials with more than 11,000 participants in the UK and Brazil.
When it comes to testing the jab’s safety, over 23,000 participants are being monitored in studies in the UK, Brazil and South Africa.
The results have so far shown the jab to be safe, with just three of the participants experiencing serious side effects that were “possibly related to a vaccine” over a three-month period.
All these participants remain in the trial and have recovered or are recovering.
When it comes to the trials being carried out around the world, critics previously argued regulatory approval tends to be granted off the back of a single large study, as was the case for the Pfizer vaccine.
The Oxford scientists have stressed their global approach was discussed with regulators and “strengthens the impact” of their results, given the vaccine was tested on “diverse populations”.
Oxford-AstraZeneca’s efficacy results
The ongoing trial set out to uncover whether the vaccine protects against symptomatic coronavirus; defined as a positive test along with a fever, cough, shortness of breath, or loss of smell or taste.
When pooling the two vaccine regimens, 30 people who received the jab developed a symptomatic infection 14 days after the second dose, compared to 101 cases in the control group.
This equates to a 70% efficacy, which can be broken down to 62% for the double full-dose regimen, and 90% when the vaccine is given at a half dose followed by a full dose.
An effective jab has long been hailed as a route back to life as we knew it, however, the scale of the pandemic means no single pharmaceutical company can roll out enough doses to stem the outbreak.
While the Oxford scientists stressed there is no competition between pharmaceutical firms, their trial is unique in that more than 6,000 of the UK participants had a weekly swab to test for the coronavirus.
This should allow the team to gauge the number of people who catch the infection but develop no symptoms.
The results reveal 69 cases of asymptomatic coronavirus emerged, of which 29 were among those who had the vaccine, compared to 40 in the control group.
This suggests the jab’s overall efficacy against asymptomatic transmission is 27%.
When broken down according to the low dose then full dose or double full dose regimens, the results come in at 59% and 4%, respectively.
“Data are most compelling for the cohort who got half a dose of the vaccine in their first jab,” said Dr Simon Clarke, from the University of Reading.
“Not only does this seem to confer greater protection against disease, it is in this group there is a reduction in asymptomatic transmission of the virus, something which is essential if herd immunity is to be obtained to get wider protection of the population.
“Unfortunately, this cohort was relatively small, reducing the reliability of the findings.”
Among the more than 23,000 participants, 10 people from the control arm were hospitalised with the coronavirus from 21 days after the first placebo dose, including two severe incidents and one death.
This is compared to no hospitalisations or severe disease cases among those having the jab. Co-author Professor Sarah Gilbert stressed this could have a “huge impact on health systems”.
The scientists added, however, the trial was not designed to specifically measure asymptomatic transmission or hospitalisation. Further research is therefore required.
‘For regulators to decide’ vaccine’s fate
Statistics have repeatedly flagged elderly people are significantly more likely to develop coronavirus complications.
In the ongoing Oxford study, the low-dose then full-dose group initially did not include participants over 55 due to the first vaccine being administered early in the trial, before older adults had been recruited.
The double full-dose regimen was given to participants of a range of ages.
Some experts previously suggested the low-dose, high-dose regimen may appear to be more effective due to the participants’ youth, rather than this being the optimal immunisation plan.
Professor Pollard argued the scientists analysed the vaccine’s effectiveness according to the participant’s age after it was requested by The Lancet.
“The difference between those groups holds up,” he said.
The initial half-dose’s efficacy does not therefore appear to be an “age phenomenon”, with this dose perhaps “priming the immune system” ahead of a full vaccine.
The scientists agreed, however, further analysis is required.
“In order to assess vaccine efficacy, we need to have a sufficient number of COVID-19 [the disease caused by the coronavirus] cases among participants to indicate that the vaccine is protecting them from disease,” said co-author Dr Merryn Voysey.
“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.”
Like with all the coronavirus vaccines, the duration of immunity is unclear.
Professor Pollard added: “All of the data gets put in front of the regulators and it’s for them to decide whether the body of data is sufficient.”
Watch: What is long COVID?