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The Sars-CoV-2 vaccine developed by the University of Oxford demonstrated average efficacy of 70.4%, according to results of clinical trials.
The interim analysis of phase 2/3 trials in the UK and Brazil found efficacy of 62% following two full doses given at least one month apart.
However, vaccine efficacy was 90% when ChAdOx1 nCoV-19, also known as AZD1222, was given to a subset of participants as a half dose, followed by a full dose at least one month later.
No hospitalisations or severe cases of the disease were reported in participants who received the vaccine, Oxford’s partner AstraZeneca said in a press release this morning.
The data also suggested a half dose and full dose regime could help to prevent transmission of the virus, according to a press release from the University of Oxford.
Sarah Gilbert, professor of vaccinology at Oxford, said: “The announcement today takes us another step closer to the time when we can use vaccines to bring an end to the devastation caused by SARS-CoV-2.”
The announcement follows promising interim data from Pfizer-BioNTech and Moderna, which recently demonstrated protection of around 95% against developing COVID-19 with their messenger RNA (mRNA) vaccines
However, the Oxford vaccine is cheaper to produce, and unlike the other vaccines that require a demanding cold chain storage, can be kept at standard refrigerator temperatures of between 2C and 8C.
Prof Andrew Pollard, director of the Oxford Vaccine Group, said: “These findings show that we have an effective vaccine that will save many lives.
Excitingly, we’ve found that one of our dosing regimens may be around 90% effective and if this dosing regime is used, more people could be vaccinated with planned vaccine supply.”
Asked why giving a half dose followed by a full dose appeared to be more effective, Prof Pollard told a briefing hosted by the Science Media Centre: “We think that by giving a smaller first dose that we’re priming the immune system differently, we’re setting it up better to respond.”
He added: “What we don’t know at this moment is whether that difference is in the quality or the quantity of the immune response, and that’s something we are doing to be digging into.”
Pascal Soriot, AstraZeneca’s chief executive Officer, said using a halved first dose and a standard second dose would mean “we can vaccinate more people, faster”.
AstraZeneca Prepares to Seek Regulatory Approval
The company said it would immediately prepare regulatory submission of the data to authorities around the world.
Trial results will be submitted to a scientific journal for peer review.
The pooled analysis included data from the COV002 Phase 2/3 trial in the UK and COV003 phase 3 trial in Brazil, and involved more than 23,000 participants.
Dr Zania Stamataki, viral immunologist at the University of Birmingham, commented: ” People will be tempted to compare efficacy between the different vaccines but we must remember that these are early data designed to achieve approval. Efficacy is not the same as effectiveness and the early numbers will change as the vaccines are rolled out.”
Dr Gillies O’Bryan-Tear, chair of policy and communications at the Faculty of Pharmaceutical Medicine, said: “The level of efficacy seen with this vaccine is well over the threshold set for these vaccines, and at the threshold required for herd immunity provided there is sufficient take-up.
“It is unquestionably more good news for the COVID pandemic, and given its much lower price than the mRNA viruses, this could be the vaccine that reaches more parts of the global community than the mRNA vaccines.”
The UK Government has ordered 100 million doses of the Oxford vaccine. That is more than the 40 million doses of the Pfizer-BioNTech vaccine, and the five million of the Moderna vaccine.
The Prime Minister described today’s announcement from AstraZeneca as “incredibly exciting”. In a tweet, Boris Johnson said: “There are still further safety checks ahead, but these are fantastic results.”