A COVID-19 vaccine made by AstraZeneca and Oxford University appears to prevent disease and can reduce coronavirus transmission.
In studies of more than 22,000 people in the UK and Brazil, the vaccine was 90 per cent effective in preventing COVID-19 when people received a half dose of the vaccine followed by a full dose a month later, AstraZeneca said on November 23. in a news release.
When participants received two full doses of the vaccine one month apart, its effectiveness dropped to about 62 percent, the company reported. It is unclear why the half dose followed by a full dose worked better than two full doses. Overall, the combined results showed that the vaccine had an average effectiveness of 70 percent among those who received the vaccine, compared with people in a control group who received a meningococcal vaccine or a placebo.
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The vaccine is the third in recent weeks to demonstrate safety and efficacy in clinical trials. The AstraZeneca vaccine may be easier to distribute than those of Pfizer and its German collaborator BioNTech and Moderna because the vaccine does not need to be frozen as the other two do (SN: 16/11/20; SN: 18/11/20; SN: 20/11/20). It can be stored at temperatures that are in normal refrigerators, unlike the special freezers needed for the Pfizer vaccine.
AstraZeneca says it has the capacity to produce 3 billion doses of its vaccine by 2021.
In the new AstraZeneca / Oxford analysis, there were 131 cases of the disease. No hospitalizations or serious cases of the disease were reported among people who received the vaccine, AstraZeneca said. The results were reported in a press release and have not yet been reviewed by independent scientists.
Unlike the Pfizer and Moderna vaccines, the AstraZeneca / Oxford vaccine is not based on mRNA, a cousin of DNA. Instead, Oxford researchers and a university-derived company called Vaccitech began with a weakened version of an adenovirus that causes colds in chimpanzees. This same chimpanzee adenovirus has been used to make a vaccine against Ebola. To fight the coronavirus, chimpanzee virus was designed to infect, but not replicate, human cells.
When it infects cells, the engineered chimpanzee virus provides instructions for making the iconic “spike” protein of SARS-CoV-2, the virus that causes COVID-19. Human cells make the ear protein, which prepares the immune system to attack the coronavirus if the person finds it later.
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It’s encouraging that all types of vaccines seem to work well in protecting against COVID-19, says Rajesh Gandhi, an infectious disease doctor at Massachusetts General Hospital and Harvard Medical School in Boston.
Moreover, the AstraZeneca / Oxford vaccine reduces the transmission of the virus by reducing the number of asymptomatic infections, vaccine developers have reported. “That’s critical because we know that a lot of SARS-CoV-2 transmission comes from asymptomatic people,” Gandhi said during a Nov. 23 news conference at the Infectious Diseases Society of America. It is unclear whether Pfizer or Moderna vaccines reduce transmission.
The FDA recommends that COVID-19 vaccines be at least 50 percent effective, meaning that one vaccine should halve COVID-19 cases compared to a placebo (SN: 10/4/20). Pfizer, Moderna and now AstraZeneca / Oxford have recorded rates above the 50 per cent threshold.
“I am delighted that several vaccines appear to be showing (effectiveness) at higher rates than we (set) as a benchmark,” Gandhi said. "They go far beyond that, so I think that's great news."
The AstraZeneca vaccine is still being tested in the United States, Japan, South Africa, Kenya, Russia and Latin America with future trials planned in other European and Asian countries. Previously, trials were stopped briefly because of a neurological disease in a volunteer in the UK trial, but were resumed after regulatory agencies deemed it safe to do so (SN: 9/9/20).
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