牛津大学新冠疫苗公布第三期临床试验结果，有效率70.4%
11月23日，牛津大学与阿斯利康联合宣布了其开发的新冠候选疫苗ChAdOx1 nCoV-2019（AZD1222）三期试验的中期试验数据，分析显示，该疫苗在调整至适当剂量后有效率可高达90%，并且可在2-8℃的正常冷藏温度下实现六个月内进行存储、运输和处理。
试验表明，当1个月内两次注射全剂量时，有效率为62%；而采取第一次一半低剂量、第二次全剂量的注射方式，其有效率达到90%。上述两种给药方案的综合有效率为70.4%。
今年8月6日，阿斯利康与康泰生物签署中国内地市场独家授权合作框架协议，根据约定，康泰生物作为技术受让方，将确保在2020年底前达到至少1亿剂新冠疫苗AZD1222的年产能，并在2021年底前将该疫苗设计产能扩大至年产至少2亿剂。
目前，英国政府已预订牛津疫苗1亿剂，预计足够5000万人接种。
The COVID-19 vaccine developed by the University of Oxford in collaboration with the pharmaceutical giant AstraZeneca could be up to 90% effective, according to data from late-stage trials.
The interim analysis from trials in the UK and Brazil, is yet another victory in the battle against COVID-19, following positive results from the Pfizer and Moderna trials, respectively, as well as the development of Chinese and Russian vaccines.
AstraZeneca, which began to manufacture the Oxford University-developed vaccine in June, said it will have as many as 200 million doses by the end of 2020 – around four times as many as Pfizer will have of its vaccine. Seven hundred million doses could be ready globally as soon as the end of the first quarter of 2021.
The vaccine was 90% effective in preventing COVID-19 when it was administered as a half dose followed by a full booster dose administered at least a month later.
Developed with the help of chimps
AstraZeneca's vaccine candidate uses a modified version of a chimpanzee common cold virus to deliver instructions to cells to fight the target virus, a traditional approach to vaccine development.
The vaccine's architect, Sarah Gilbert, from the University of Oxford, says the technology used to develop the vaccine, on which her team has been working for the past several years, is "very adaptable." She adds: "We can quickly turn to a different purpose to make a vaccine against a new pathogen."
More than 10 years ago, the technology was being used to develop a vaccine for influenza, while Gilbert's team had developed a vaccine against Middle East respiratory syndrome (MERS), another coronavirus.
The work the team did on MERS, showed Gilbert "that they could make a [coronavirus] vaccine with this technology that would induce good immune responses against a coronavirus spike protein."
The vaccine, derived from the chimp virus, initially is modified so it cannot multiply in humans. Scientists then add the genetic instructions for the coronavirus's specific spike protein, which emit from the surface of the virus and is used to invade human cells.
Once injected, the vaccine uses this genetic code to produce the spike protein, which is then detected by a subject's immune system causing an antibody response. The response can also attack the real virus should a subject become infected in the future.
Half-dose/full-dose
The effectiveness of AstraZeneca's vaccine depended on the dosing, and fell to 62 percent when given as two full doses rather than a half-dose first.
Scientists have cautioned against seeing this as evidence that it would be less useful than rivals. Vaccines from Pfizer and Moderna each prevented about 95 percent of cases according to interim data from their late-stage trials.
Andrew Pollard, director of the Oxford Vaccine group, which invented the vaccine, said that work is ongoing to determine exactly why the half-dose/full-dose worked better.
"We think that by giving a smaller first dose we are priming the immune system differently, we are setting it up to respond. What we don't know in this moment is whether that difference is in the quality or the quantity of the immune response."
Pascal Soriot, AstraZeneca's CEO, said the information showing that an initial half dose was more effective than two full doses was good news, as more people could be vaccinated faster with a limited supply.
'Fridge temperatures'
The vaccine's developers explicitly want their product to be "for the world," rather than for wealthier countries with developed infrastructure for administering the drug.
That the AstraZeneca vaccine can be stored at "fridge temperatures" should make its distribution far easier in the global south. Especially when compared with Pfizer's candidate, which needs to be shipped and stored at -70 degrees Celsius, the sort of temperature typical of an Antarctic winter.
The vaccine's manufacturing will now be ramped up, according to Soriot, so AstraZeneca can provide hundreds of millions of doses starting from January 2021. The UK is well placed to receive the vaccine should it be approved, ordering 100 million doses in July, an early signal of confidence in the University of Oxford's work.
Cheaper than its rivals
The vaccine is also set to be cheaper than its rivals, in part due to its reliance on established technology. AstraZeneca, one of the world's leading biopharmaceutical companies, has pledged not to profit from the vaccine "during the pandemic" and has its price at around $2.50 a dose. Based on its agreements with the U.S. government, Pfizer's vaccine is set to cost around $20 a dose and Moderna's between $15 and $25.
AstraZeneca will now immediately prepare regulatory submission of the data to authorities around the world that have a framework in place for conditional or early approval.
It will also seek an emergency-use listing from the World Health Organization to speed up availability in low-income countries. In parallel, the full analysis of the interim results is being submitted for publication in a peer-reviewed journal.