The second vaccine, made by Oxford/AstraZeneca, is based on technology that has been successfully used before: a harmless chimp cold virus tweaked so that it carries genetic material containing the instructions for the spike protein.Ĭlinical studies evaluating the Oxford-AstraZeneca vaccine did include spacing doses by two to three months, which appeared to trigger a stronger immune response. There is some evidence that delaying the second dose of the Oxford/AstraZeneca vaccine could be beneficial Meanwhile, the companies themselves issued a statement saying: ‘There is no data to demonstrate that protection after the first dose is sustained after 21 days.’Ģ. However, UK officials suggested that in the trial most of the ‘vaccine failures’, where people got Covid-19 despite having been vaccinated, were in the period shortly after the first dose. Between day 15 and 21, the observed efficacy against symptomatic Covid-19 was estimated at 89%, leading officials to conclude that ‘short term protection from dose 1 is very high from day 14 after vaccination’.īut scientists have underscored that the levels of so-called neutralising antibodies - which immunologists contend are the most formidable weapons of the immune arsenal - appear to increase dramatically only after the second dose. In a peer-reviewed study, the companies showed that the efficacy of the vaccine was 52.4% between the first and second dose - which were spaced 21 days apart. Trials for this vaccine did not test different dose gaps, nor did they evaluate the impact of one versus two doses. Two weeks after the second dose, the vaccine showed a spectacular efficacy of 95%. The first vaccine - from Pfizer/BioNTech and now being rolled out across Europe - uses new technology that introduces genetic material, called mRNA, which contains the instructions to make the so-called spike protein of the coronavirus into the body to elicit an immune response. When UK officials announced the new guidelines, two vaccines had been authorised for use. There is little trial evidence to show what impact this will have on the Pfizer/BioNTech vaccine Here are five things to know about the evidence and potential implications of delaying vaccine doses.ġ. However critics question the wisdom of moving away from the timetable tested during clinical trials. The rationale is that, with the virus raging alongside uncertainty about vaccine supply, vaccinating a greater number of people with a single dose would be more effective at preventing deaths and hospitalisations than if a smaller number of people received two doses.
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