New analyses of the AstraZeneca/University of Oxford COVID-19 vaccine revealed that a single standard dose efficacy from day 22 to day 90 post vaccination of 76%, with protection not falling in this three-month period.
South Africa has recently received its first consignment of one million doses of the Covishield vaccine from India. This vaccine is based on the AstraZeneca/University of Oxford vaccine.
This vaccine is based on a chimpanzee adenovirus vaccine vector. This is a harmless, weakened adenovirus that usually causes the common cold in chimpanzees.
It was chosen as the most suitable vaccine technology for a COVID-19 vaccine as it has been shown to generate a strong immune response from one dose in other vaccines.
It has been genetically changed so that it is impossible for it to grow in humans. This also makes it safer to give to children, the elderly and anyone with a pre-existing condition such as diabetes.
Chimpanzee adenoviral vectors are a very well-studied vaccine type, having been used safely in thousands of subjects.
The AstraZeneca/University of Oxford vaccine has previously been shown to have an efficacy of between 63% and 90% on two doses.
An analysis of further data has now shown that the vaccine efficacy is higher at longer prime-boost intervals, and that a single dose of the vaccine is 76% effective from 22 to up to 90-days post vaccination.
The effect of dosing interval on efficacy is pronounced, with vaccine efficacy rising from 54.9% with an interval of less than six weeks to 82.4% when spaced 12 or more weeks apart.
A single standard dose of the vaccine is 76% effective at protecting from primary symptomatic COVID-19 for the first 90 days post vaccination, once the immune system has built this protection 22 days after the vaccination, with the protection showing little evidence of waning in this period.
Professor Andrew Pollard, chief Investigator of the Oxford Vaccine Trial, said this finding supports the policy recommendation for a 12-week prime-boost interval.
The exploratory analyses suggest that it is the dosing interval and not the dosing level which has a great impact on the efficacy of the vaccine.
This is in line with previous research supporting greater efficacy with longer prime-boost intervals done with other vaccines such as influenza, Ebola, and malaria.
Further good news is that the vaccine has the potential to reduce transmission of the coronavirus, based on swabs obtained from volunteers in the UK with a 67% reduction after the first dose of the vaccine.
The researchers hope to report data regarding the new variants in the coming days, and expect the findings to be broadly similar to those already reported by fellow vaccine developers.