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Oxford-AstraZeneca COVID-19 vaccine 70% effective: Lancet

Vivek Punj     December 9, 2020

Medical journal Lancet has reported that the coronavirus vaccine developed by British-Swedish pharmaceutical company AstraZeneca and Oxford University is 70.4 per cent effective against the coronavirus. This is the first time that the efficacy result of a COVID-19 vaccine candidate has been published in a scientific journal.  

The Lancet report noted that the Oxford-AstraZeneca chimpanzee adenovirus vectored vaccine against coronavirus christened ChAdOx1 nCoV-19 or AZD1222 was found 70.4 per cent effective 14 days after two standard doses which had a gap of 28 days between them.  

Interim efficacy results were reported for ongoing trials in the UK and Brazil involving 11,636 participants. Out of them, 131 volunteers contracted COVID-19 - 30 from the group that received the vaccine and 101 from the control group. A group in UK trials had received half-dose of the vaccine as the first dose, followed by a standard dose.

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The publication pointed out that surprisingly the vaccine candidate was 90 per cent effective when a low dose was followed by a full dose (LD/SD cohort). Two standard doses (SD/SD cohort) yielded efficacy of only 62.1 per cent.  

Similar efficacy was observed after 21 days from the first standard dose, suggesting there was at least short-term protection with one dose. As for asymptomatic cases, the vaccine efficacy was significantly lower - 58.9 per cent when administered in a low dose/standard dose combination, and only 3.8 per cent in standard dose/standard dose group, and only 3.8 per cent in a standard dose-standard dose combination.  

The results nonetheless provided some hope that COVID-19 vaccines might be able to interrupt some asymptomatic transmission, although fewer data were available with this outcome and more data is needed to confirm, Lancet noted.  

"Only 1,418 (12.1 per cent) of those assessed for efficacy were older than 55 years (none of whom were in the LD/SD cohort), meaning that from the interim analysis of these trials, we cannot yet infer efficacy in older adults, who are the group at greatest risk of severe COVID-19 outcomes," the article stated.  

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Lancet noted that there were 175 serious adverse events - 84 in the vaccine group and 91 in the control group. Three of these were possibly related to the intervention, including transverse myelitis occurring 14 days after a ChAdOx1 nCoV-19 booster vaccination, haemolytic anaemia in a control recipient, and fever higher than 40-degree Celsius in a participant still masked to group allocation, the journal added.  

Two additional transverse myelitis cases, considered unlikely to be related to the intervention, also came to light - one 10 days after the first dose of the Oxford-AstraZeneca vaccine, another one in a control group that occurred 68 days after vaccination. The transverse myelitis cases resulted in a temporary halt to the trial and all participants have recovered or are recovering, the journal said.  

This is a positive development for India, as the country is expecting the Oxford-AstraZeneca vaccine to be one of the first vaccines to get emergency use authorisation (EUA). Pune-based Serum Institute of India (SII) has collaborated with AstraZeneca and Oxford University for manufacturing and distribution of the vaccine as Covishield in India. The company has already filed for emergency use authorisation for the vaccine. 

Also Read: Pfizer seeks approval for emergency use in India after nod in UK, Bahrain


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