Could having a common cold protect you against Covid-19? The intriguing prospect has been raised by a team from the La Jolla Institute for Immunology in California. They were researching the response of human T cells – which play a vital role in the immune system – in patients who have recovered from Covid-19. The response they detected, however, also showed up in 40 to 60 per cent of a control group that had not been exposed to Covid-19. In a paper published in the journal Cell they write: 'This may be reflective of some degree of crossreactive, pre-existing immunity to Sars-CoV-2 in some, but not all, individuals'. Sars-CoV-2 is the virus which causes Covid-19.
In other words, if you have a common cold – which, like Covid-19, is caused by coronaviruses – that can lead you to develop an immune response to that particular coronavirus. But that immunity then also protects you, to some extent, to infection by Sars-CoV-2. The team does then add 'Whether this immunity is relevant in influencing clinical outcomes is unknown', but it does raise the possibility that many of us might have some natural degree of protection against Covid-19 – contradicting the presumption of government scientific advisers that 80 per cent of the population would catch the virus if it were allowed to rip through the population without lockdowns of social distancing. In the one real-life accidental experiment into the spread of Covid-19 – the cruise ship the Diamond Princess, where the virus was allowed to spread unchecked for a fortnight – only 17 per cent of the 3,711 passengers and crew contracted the virus.
The La Jolla team notes that crossreactive immunity from other influenza viruses helped protect the population during the outbreak of H1N1 swine flu in 2009 – which was declared a pandemic by the World Health Organisation but turned out to be far milder than many people feared.
The La Jolla study backs German research suggesting that 34 per cent of the population have T cells that recognise Sars-CoV-2, without previously having encountered the new virus. The virologists behind that work were keen to stress that this did not mean a third of us are immune from Covid-19 but it could explain why some people have only very mild symptoms or are asymptomatic.
The main point of the La Jolla research was to help understand the human immune response in order to develop new vaccines.