New research has revealed that some forms of the common cold can offer protection against Covid-19, thanks to residual infection-fighting T-cells that prevent the virus from taking hold.

The study, by University College London (UCL) and published in the journal Nature, monitored a group of 750 healthcare workers in the first wave of the pandemic and found that 58 never tested positive, despite being in a high risk environment. 

 “We think people (who resisted the infection) already had some T-cells from previous infections and that allowed them to mount a very quick response that could abort the infection,” explains Professor Mala Maini, study co-author from UCL. “We’ve identified T-cells, which are able to target an inner part of the virus involved in the replication in the early steps of the life cycle.”

Does this mean that we should be actively courting the common cold in order to boost our immunity against Covid?

“No, definitely not,” says Professor Mala Maini. “Only 10 per cent of what we recognise as common colds are actually caused by coronaviruses, so just because you had a common cold doesn’t mean you’ve actually had a coronavirus. Also, the T-cell response you get is quite variable, depending on your genetic background, and wouldn’t necessarily be strong enough to fight off the new variants that we’ve got now. 

“We don’t want the message to be, oh, if you’ve had a common cold, you can fight off Covid, because that is quite misleading. It’s that by studying that group, we’ve been able to pick out a type of immune response that isn’t currently being harnessed but could be going forward.”

If I’ve already had Covid does that mean I will have these ‘pre-emptive’ T-cells?

 “If you’ve had a sort of classical Covid infection, you’re not as likely to have T-cells that target this stage – the inner replication machinery of the virus – as those who resisted the infection and who just got this abortive type of infection,” explains Prof Maini. “But you will have all sorts of other useful immune responses – both antibodies, B cells and T cells – that target the different parts of the virus.”

What is the classic immune system response to Covid?

 “There is an antibody response – antibodies are made by the B cells – which is supported by the T-cells,” explains Prof Mala Maini. “It’s really ideal if you have all those components working together.

“Antibodies are very good at preventing infection from getting into the cells but, if some of the virus gets into your cells, the T-cells can do a great job at clearing those infected cells. That’s why it’s important to think about the two working hand-in-hand.

“People have always thought of T-cells as being a secondary line of defence that comes later on. But what’s interesting is our work and several other studies on Covid, are showing that they can actually act very, very early on. And we think the way they’re doing that is because they’ve already been primed by a previous infection. So they’re in a state where they can kick into action much quicker than normal.” 

How are the vaccines we have at the moment, such as the AstraZeneca and Pfizer, working on our immunity?

“All the vaccines we have are focused on the protein spike (of the virus). So they coat the surface of the spike and stop it entering the cell.”  The study suggest that vaccines could be even more effective if they include other regions of the virus. She adds: “The replication complex is a particularly exciting region to include because it’s expressed in the first step of the life cycle.”

Could we soon see a new type of vaccine that’s better at preventing infection?

“The current vaccines do reduce infection rates, but looking forward it’s about trying to do an even better job. It’s about adding another layer of protection by targeting and generating T-cells to the (early) inner replication machinery.

“What we’re saying is let’s specifically target both the spike, which we’re already doing, and this new area. It is still really important to have those antibodies to the spike, because they’re very good at preventing the virus from getting into the cell. They are also reducing infection rate, but not as much as we ideally would like.”

How effective are the current jabs at preventing infection?

“All the vaccines we have in the UK are surprisingly effective,” says Prof Charles Bangham, Professor of Immunology, Imperial College London. “Each study shows a slight difference, but generally, after two doses of any of the vaccines, it seems that you have roughly 90 per cent protection against the existing variants, and often between 70 and 90 per cent, even against the Delta.

“But more recently, the estimates of protection against Delta have gone down.The apparent decrease in protection might be caused by a combination of three things, either because the Delta variant is more infectious and grows to a higher level, because the immunity that was elicited by the vaccine is waning or because people are now mixing more than earlier in the pandemic. Probably all three factors contribute but we don’t know which one is more important. So that is still a question that has not really been properly answered.”

How quickly does our immunity wane after an infection or a vaccine?

“It’s not clear whether the level of immunity is really waning or whether more people are getting infected.  Either it’s that we’ve got more people mixing now than we did in the summer and children have gone back to school, or it’s because the Delta variant is now the one that’s dominant and more infectious,” says Prof Bangham. “My own belief is that it is probably more down to increased mixing and the Delta variant rather than waning immunity, but we need proper data.”