Why have some people never caught Covid? The answers could help protect us all
Zania Stamataki
I’m a Covid researcher, but I’ve never tested positive. Studying variations in immune systems could lead to better vaccines
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A doctor injecting a patient with the Covid-19 vaccine.
‘There is also a possibility that different immune systems respond differently to the virus.’ A doctor injecting a patient with the Covid-19 vaccine. Photograph: Westend61 GmbH/Alamy
Mon 7 Mar 2022 03.00 EST


I’m one of the fortunate people who is yet to test positive for Covid. This is despite the fact that I work with live replicating Sars-CoV-2 (the virus that causes Covid) for my research, teach face-to-face at university, and have school-age children.

My fully vaccinated healthy friends of the same age were not so lucky, and some have suffered from more than one case of Covid in the past couple of years. What does this reveal about my immune system?

First, we have to consider a number of scenarios. There is a very small chance that I have never come into contact with the virus. But given the duration of the pandemic, and the number of highly transmissible variants, this is unlikely. Then there is the chance that I have come into contact with Sars-CoV-2, but it was cleared from my body quickly before it developed into the disease Covid (abortive infection). At the start of the pandemic, and before I was vaccinated, I could have caught the virus but I could have been one of the small number of people who did not display symptoms and therefore did not test for it.

Some people may clear the virus quickly because they have pre-existing antibodies and memory immune cells that recognise the virus. These could be cross-reactive memory T-cells generated previously to fight similar coronaviruses that cause the common cold. There is evidence of higher prevalence of endemic (non-Covid) coronavirus infections in the young and reduced cross-reactive T-cell presence in older people.

When vaccines became available, I received my first and second doses, along with a booster shot. Vaccines work by introducing our immune system to the virus spike protein, and setting off an early arsenal of specific antibodies and T-cells. These leave memory cells behind, which can persist for years and spring into action to prevent reinfection.

Although Covid vaccines still protect from severe disease, each time there is a new variant we scientists frantically search for any evidence of vaccine escape in real-life data. We can’t predict vaccine escape because we are not observing stepwise virus evolution, where emerging strains add new mutations to their predecessors; the now-prevalent Omicron variant has few similarities with Delta, which was spread widely last year. Natural infection does not offer long-term protection, and the more potent vaccine-induced immunity needs a booster to protect against variants.-- excerpt, rest at link above --