Introduction On November 9th, 2020, Pfizer announced that its vaccine “was found to be more than 90% effective in preventing COVID-19 in participants without evidence of prior SARS-CoV-2 infection” (Ref 1). That was the first such announcement from any of the number of trials trying to develop a vaccine for the virus SARS-CoV-2, which can cause the disease Covid-19. The press release reported that 43,538 participants had been enrolled and that 94 cases of Covid-19 had been confirmed among the participants (Note 2). On December 10th, 2020, an academic paper followed the Pfizer announcement (Ref 3). It was called “Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine”. The Oxford/AstraZeneca announcement followed a month later and it was accompanied by an academic paper published in The Lancet on December 8th, 2020 (Ref 4). The paper in The Lancet was a follow-up to another paper in the same journal published on July 20th, 2020 (Ref 5). The Oxford/AstraZeneca team also published a paper on November 18th, 2020, which reported on a trial specifically undertaken in younger and older adults than those studied in the July and December papers (Ref 6). This note primarily reviews the Lancet publications about the safety and efficacy of ChAdOx1 nCoV-19, the Oxford/AstraZeneca vaccine. References to the Pfizer vaccine are also made where appropriate. The two vaccines are different and both use new techniques. ChAdOx1 nCoV-19 is a chimpanzee adenovirus vaccine vector. Coronaviruses have spikes on their outer coats (which is why they look like a crown and which is where they get their "corona" name from). The Oxford/AstraZeneca vaccine contains the genetic sequence of the surface spike protein. When the vaccine enters cells in the body, it uses this genetic code to produce the surface spike of the coronavirus to induce an immune response (Ref 7). The first adenovirus-based vaccine (a vaccine for Ebola, made by Johnson & Johnson) was approved for general use in July 2020 (Ref 8).
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