Adding more colour to the race for a COVID-19 vaccine, developers of the Russian vaccine candidate Sputnik V called on AstraZeneca to experiment combining vaccines with theirs. The Russian vaccine developers in a tweet late on Thursday said AstraZeneca should try combining its experimental shot with the Russian Sputnik V to boost efficacy and combining vaccines may prove important for revaccinations.
Sputnik V's comment came right after reports that AstraZeneca is likely to run an additional global trial to assess the efficacy of lower dosing regimen of its vaccine. Bloomberg News quoted AstraZeneca CEO Pascal Soriot as saying that it is looking to conduct an additional global trial instead of adding a trial arm to its ongoing trials in the US, after questions were raised over the results from its late-stage study.
Sputnik V said, "Current full dose AstraZeneca regimen resulted in 62% efficacy. If they go for a new clinical trial, we suggest trying a regimen of combining the AZ shot with the Sputnik V human adenoviral vector shot to boost efficacy. Combining vaccines may prove important for revaccinations."
In an interim analysis of late-stage trials, AstraZeneca had reported 90% vaccine efficacy for a lower dosing regime and 62% for two full vaccine doses. It later admitted that lower dosing was not by design but an error in the trial, drawing strict criticism on the transparency of trial protocols and push for the company to attempt fresh trials.
Sputnik V had last week in its second interim report assessed 39 COVID-19 confirmed cases among trial participants and reported 95% efficacy 40 days after the first dose. However, most experts say it is a very small pool of confirmed cases to extrapolate vaccine efficacy results and Russia needs to wait for more cases to accrue to make an informed decision on efficacy.
This is Russian vaccine developers' second call to AstraZeneca for combining vaccines. On November 23rd when AstraZeneca reported its interim analysis, Sputnik V developers had said, "Sputnik V is happy to share one of its two human adenoviral vectors with AstraZeneca to increase the efficacy of AstraZeneca vaccine. Using two different vectors for two vaccine shots will result in higher efficacy than using the same vector for two shots."
"The possible reason for 62% efficacy of AstraZeneca’s full dose regiment is that immunity to chimpanzee adenoviral vector from the 1st shot makes 2nd shot not effective. Sputnik V addresses this issue by using two different human adenoviral vectors for two shots (92% efficacy)," it added.
AstraZeneca’s vaccine candidate is based on chimp adenovirus vector. Viruses that cause common cold in chimpanzees are genetically modified to insert Sars-Cov2 protein codes to stimulate an immune response in the human body when administered.
Sputnik V vaccine alternatively is based on human adenoviral vector. Human adenoviruses are similarly genetically modified with Sars-Cov2 spike protein codes to trigger an immune response in the body. The Russian vaccine uses two different strains of human adenoviruses (rAd26 and rAd5) for the first and second vaccination dose, to boost the effectiveness of the vaccine.
Johnson & Johnson's single-dose vaccine under development is also based on an adenovirus vector. There are more than 13 vaccine candidates in late-stage human trials across the world.
AstraZeneca and Oxford University have partnered with Pune-based Serum Institute of India (SII) for the manufacturing of its coronavirus vaccine and the Indian partner is also conducting a bridge Phase 2/3 trial in India. Sputnik V has tied-up with Indian drug maker Dr Reddy's Labs for a similar arrangement.