By Dr Lindsay Broadbent, PhD, Queen’s University Belfast — The Conversation, 18 May 2022
More than 60% of people in the UK have tested positive for COVID at least once. But even taking into account people who have had COVID and not realised it, there is still likely a group of people who have never been infected. Due to the high level of community transmission, particularly with the extremely transmissible Omicron variants, it’s very unlikely that someone going to work or school, socialising and shopping hasn’t been near someone infected with the virus. Yet there are people who have experienced high levels of exposure, such as hospital workers or family members of people who have had COVID, who have somehow managed to avoid testing positive. The reason why some people appear immune to COVID is one question that has persisted throughout the pandemic.
One theory is that although these people are exposed to the virus, it fails to establish an infection even after gaining entry to the airways. This could be due to a lack of the receptors needed for SARS-CoV-2 to gain access to cells. There’s also the possibility that a quick and robust immune response could prevent the virus from replicating to any great degree. Scientists studying severe COVID have identified a genetic cause in nearly 20% of critical cases. Just as genetics could determine disease severity, genetic makeup may also hold the key to resistance to SARS-CoV-2 infection. In research on nasal cells from human donors, one donor’s cells could not be infected with SARS-CoV-2 at all, with interesting genetic mutations identified that could explain why — including a mutation in a gene involved with sensing the presence of a virus previously shown to confer resistance to HIV infection.
There’s also the possibility that previous infection with other types of coronaviruses results in cross-reactive immunity, where our immune system may recognise SARS-CoV-2 as similar to a recently encountered virus and launch an immune response. If you’ve managed to avoid COVID to date, maybe you do have natural immunity to SARS-CoV-2 infection, or perhaps you’ve just been lucky. Either way, it’s sensible to continue to take precautions against this virus that we still know so little about. This article has been republished under Creative Commons licence.