What is cross immunity? Thanks for asking!

Until recently, it’s been assumed that nobody had pre-existing immunity to COVID-19. Experts and world leaders such as Angela Merkel warned that the virus could go on to infect up to 70% of a country’s population, if it wasn’t eliminated. But studies are suggesting some people may already be resistant. We’ve already talked about herd immunity in a previous episode. Some countries like Sweden opted not to enforce strict lockdown measures, in the belief herd immunity would come about naturally. That scenario still seems a long way off, but scientists are looking into another kind of immunity, known as cross immunity. Basically, some of us may already be immunised against covid-19, due to past viral infections.

But Covid-19 is a new disease. How could we have already encountered it in the past?

SARS-COV-2, the strain which causes COVID-19, is a novel coronavirus. So no-one had ever been exposed to it before it appeared in late 2019. But it is just one member of the coronavirus family. Human coronaviruses were first discovered in the 1960s, so they have existed for many decades. Our bodies defeat viruses thanks to the antibodies created by our immune systems. Generally speaking, any one type of antibody is effective against a unique type of antigen. But sometimes, antibodies are able to bind to other types of antigens with similar structures. This is described as cross reactivity. Recent research looked at antibodies recovered from survivors of the SARS epidemic of the early 2000s. That was caused by SARS-CoV-1, which is closely related to the current coronavirus strain. In-vitro tests found the antibodies had a ‘robust’ cross-reactive immune response to SARS-CoV-2.

Well SARS only affected 8,000 people; what about the rest of us? In under 3 minutes, we answer your questions!

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