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| Russia’s Sputnik V vaccine against coronavirus. Photograph: Kirill Kudryavtsev/AFP/Getty |
UK and Russian scientists are to test whether combining shots of the Oxford/AstraZeneca and Sputnik V coronavirus vaccines could result in better protection than two doses of the same one.
Trials will start by the end of the year, the Russian Direct Investment Fund (RDIF), which funded the development of the Sputnik V vaccine by Russia’s Gamaleya Institute, said on Friday. AstraZeneca confirmed that it was considering how it could assess combinations of different vaccines, and would soon begin exploring with the Gamaleya Institute whether their two vaccines could be successfully combined.
Like the Oxford/AstraZeneca vaccine, the Russian Sputnik V shot is based on a modified version of adenovirus, a common cold virus. This “vector” is stripped of any disease-causing genes and modified to carry genetic instructions for making the coronavirus spike protein, which it passes to human cells. The manufactured coronavirus spike protein then triggers an immune response that protects against the Covid-19 disease.
A potential problem with such vaccines, however, is that of “anti-vector immunity”, where if the immune system has previously encountered the type of adenovirus used in the vaccine, it may destroy it before the vaccine can trigger an immune response. This is why the Oxford University group chose to use a chimp adenovirus, rather than a human one. However, anti-vector immunity could also reduce the efficacy of booster shots, if this involves injecting the same virus for a second or third time.
Mixing and matching different vaccines may provide a solution. This concept is known as a heterologous prime-boost, and has been used in vaccination programmes against other diseases.
Unlike AstraZeneca’s vaccine, Sputnik V uses two different human adenovirus vectors to try to trigger a stronger and longer-term immune response. It is not yet clear which of these components will be tested alongside the AstraZeneca vaccine.
Anti-vector immunity could also provide a possible explanation of why the AstraZeneca vaccine appears to work better when given as a half-dose followed by a full one, rather than two full doses.
Earlier this week, the outgoing chair of the UK’s vaccine taskforce, Kate Bingham, announced that a trial of AstraZeneca’s vaccine in combination with the Pfizer shot was likely to begin in January. “It’s to do with trying to trigger the immune response and the durability [of the response],” she said.
RDIF said it approached AstraZeneca about the possibility of combining its vaccines on 23 November.
“This could eventually extend the duration of immunity and possibly also protect against people receiving the same vector repeatedly and having a less robust response,” said Beate Kampmann, the director of the vaccine centre at the London School of Hygiene & Tropical Medicine. “But for now these are all theoretical concepts that need to be carefully tested before they can be extended to population use.”
Russia is likely to see the move as a vote of confidence by a western manufacturer in Sputnik V, which is already being used to immunise medical workers, teachers and social workers. Russian officials previously announced that the vaccine had more than 95% efficacy, giving it a success rate comparable to vaccines being developed by Pfizer and Moderna.
“The decision by AstraZeneca to carry out clinical trials using one of two vectors of Sputnik V in order to increase its own vaccine’s efficacy is an important step towards uniting efforts in the fight against the pandemic,” said Kirill Dmitriev, chief executive of RDIF. “We hope that other vaccine producers will follow our example.”
Dr Stephen Griffin, associate professor in the school of medicine, University of Leeds, said: “The importance of a second jab should not be underestimated as it is important for the longevity, specificity and effectiveness of the response to most vaccines.”
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