Phase one human trials of a Covid-19 vaccine being developed by researchers at the University of Oxford suggest it triggers two types of immune response, unnamed sources working on the vaccine told ITV’s Robert Peston. Not only does the jab trigger the production of antibodies – proteins that can bind to the virus, preventing it from entering cells and flagging it to immune cells – but it also seems to result in the production of “killer” T cells – immune cells that attack infected human cells.
Is it surprising?
“Virtually any vaccine inevitably does this,” Danny Altmann, a professor of immunology at the Imperial College London, told the Guardian. Dr Zania Stamataki, a senior lecturer in viral immunology at the University of Birmingham, said questions remained, but the findings were prompting sighs of relief among immunologists. “What we do know, is that the vaccines are able to elicit the right type of immune response. This is a very encouraging sign,” she said.
Why is it exciting?
The results offer further hope that the Oxford vaccine could work against Covid-19. “When immunologists study protective immunity against any pathogen, they’re actually studying many different readouts from different cell types and mediators of the immune system. It can be hard to define, of all these, which is the absolute ‘correlate of protection’ – the level your vaccine would need to attain to maximise protection,” said Altmann.
“The results from Oxford yesterday add some detail to this discussion, with the good news that the two most obviously key parts of immune protection are effectively induced: antibodies that can neutralise virus entry, and T cells that can recognise and attack infected cells.”
It is not the only vaccine that appears to trigger both antibody and T-cell responses: a different type of vaccine, produced by the US company Moderna and based on viral RNA, also appears to stimulate both paths.
What does this mean for immunity?
So far, that is unclear, and some scientists have been unwilling to comment on the findings on the Oxford vaccine, at least until the full study is published in the Lancet on Monday. But one thing is for sure: there is still a long way to go to show that the Oxford vaccine can guard against Covid-19, despite hopes that it could be ready by September. “The big next steps will be to head into appraisal of actual protection,” said Altmann.
Stamataki agreed, noting that the two key questions were whether the immune responses generated by the various vaccines under development can protect against severe disease, and if so, for how long.
One issue is that recent studies have found that antibodies in people who have had Covid-19 drop off steeply over a three-month period after infection. A key question is whether the same drop off is seen in antibodies triggered by the vaccine.
Altmann said both the Moderna and Oxford vaccines triggered an immune response in a different way to natural infection, meaning this would not necessarily be expected. But even if antibodies do wane, the body might still be able to produce them much faster next time, while T cell response tends to last longer and so might offer longer-lasting protection.
“The duration of antibody and T cell responses is different for every vaccine and cannot be predicted accurately,” Stamataki said. “It is also different for any natural infection, so we have to wait and see how long our volunteers carry antibodies and T cells specific for Sars-CoV-2.”