The Oxford Covid-19 vaccine has been 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 three participants have recovered or are recovering, and remain in the trial, Prof Andrew Pollard from the University of Oxford, who is the lead author of the study, said while addressing a virtual media conference following the publication of the interim results of the Oxford Covid-19 vaccine trials in The Lancet on Tuesday.
The results are the first full peer-reviewed efficacy results to be published for a Covid-19 vaccine. According to the results, the vaccine protects against symptomatic disease in 70 per cent of cases, with vaccine efficacy of 62 per cent for those given two full doses, and of 90 per cent in those given a half, and then a full dose .
The Oxford vaccine uses a chimpanzee adenovirus viral vector that can’t 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, teaching the immune system to recognise and attack the virus.
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, said Prof Pollard. Those are events that investigators considered medically significant and ranged from a broken leg to a heart attack, he said.
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 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, study authors have said in The Lancet.
Data was analysed from 23,745 adults in the UK, Brazil and South Africa (11,730, 10,002, and 2,013 in the three countries, respectively). The interim analysis pools the data, 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, said Prof Pollard.
The primary outcome of the study was to determine how many cases of symptomatic Covid-19 disease 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 one 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 0.5 per cent cases in the vaccine group and 1.7 cent cases in the control group, which equates to a vaccine efficacy of 70 per cent. Cases of severe disease and hospitalisation were monitored for in all 23,745 participants. From 21 days after the first dose, there were 10 cases hospitalised for Covid-19, all in the control arm, and two were classified as severe, including one death. These are also secondary outcomes and will require additional confirmation, said study co-author Professor Sarah Gilbert from University of Oxford.
“Despite global spread of Covid-19, a large proportion of the population in many countries have not been infected and are not immune. Vaccines may play an important role in increasing immunity, preventing severe disease, and reducing the health crisis, so the possibility that more than one efficacious vaccine may be approved for use in the near future is encouraging. Here, we have shown for the first time that an adenoviral vectored vaccine – a type of vaccine technology which has been in use since 2009 – is efficacious and could contribute to disease control in the Covid-19 pandemic,” she said.
Writing in a linked Comment in The Lancet, Dr Maria Deloria Knoll and Dr Chizoba Wonodi, Johns Hopkins Bloomberg School of Public Health, USA (who were not involved in the study), say, “Oxford–AstraZeneca’s US$2–3 per dose agreement with the COVAX facility holds good promise for equitable access for low and middle-income countries, compared with the high cost of the two mRNA vaccines that have also reported more than 90 per cent efficacy.”
“Despite the outstanding questions and challenges in delivering these vaccines, it is hard not to be excited about these findings and now the existence of three safe and efficacious Covid-19 vaccines, with 57 more in clinical trials. With a range of manufacturers, a very large global investment in production and cooperation in procurement and distribution, it seems likely that 2021 will see Covid-19 vaccines made available to all countries in the world. Perhaps by this time next year, we can celebrate the global control of SARS-CoV-2, in person,” they said.
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