BELIEVE it or not, there is still a huge chunk of people who claim to never have had Covid.
You likely know at least one person who has dodged the virus despite having plenty of opportunity to be infected.
Or perhaps you are part of the no-Covid club yourself.
This club is around 30 million strong, according to modelling from Cambridge University in February.
They said around half of the UK’s adults are still yet to have the bug for the first time, MailOnline reported.
Many of us will be familiar with this scenario during the pandemic; one member of the family starts to experience the telltale signs of coronavirus, gets tested, and returns a positive result.
Others in the same home get struck down.
But there is one lucky soul who manages to avoid catching it entirely.
But why does this happen?
Experts, including Richard Stanton, professor of virology at the School of Medicine at Cardiff University, gave some explanations.
1. Genetics
Immunity differs from one person to the next partly due to their genetic makeup.
Prof Stanton said: “People have differences in how good their immune system is due to having different genes.
“Some people’s immune systems are just ‘better’ at fighting off the virus.”
A number of studies have made links between genetics and immunity during the Covid crisis.
For example, researchers at Oxford University poinpointed a chunk of DNA that doubles the risk of Covid death – and people from South Asian heritage are more likely to carry it.
Imperial College London have found that variations between people’s immune systems “makes a difference at least to whether or not you get symptomatic disease”.
The research is focused on different human leukocyte antigen (HLA) genes, with some HLA types linked to a higher or lower risk of symptomatic Covid illness.
Danny Altmann, professor of immunology at Imperial, said: “The key genes that control your immune response are called HLA genes.
“For example people with the gene HLA-DRB1*1302 are significantly more likely to have symptomatic infection.”
Another team theorised that people who are good looking have better immunity, and are therefore less likely to have had Covid so far.
2. Previous infections
Immunity built from prior infection is not something you can measure.
But it could be the reason why your friend has still avoided a bout of Covid illness.
Prof Stanton said: “It’s possible that a previous infection with certain common cold viruses can leave you with enough immune ‘memory’ to handle Covid better.”
Studies have suggested that there is some crossover between protection against a common cold, and protection against Covid.
It would suggest that, even if somebody is exposed to Covid, and picks it up, their immune system boot it out before it can cause symptoms.
Imperial College London scientists found that common coughs and sneezes boost vital white blood cells called T cells, which can recognise a range of viruses.
Immunity against bugs generally dropped massively due to lockdowns, so it’s not clear how relevant this layer of protection is.
3. Variants
We’ve seen a number of Covid variants over the past two years – Alpha, Delta, Omicron and Beta to name a few.
Some strains have biological advantages that make them more easily spread, including in households.
By the same token, it may explain why the people you live with did not pick up the bug.
Prof Stanton said: “Omicron is more transmissible than Delta and so we see that family members are more likely to be infected if someone in the household has Omicron compared to Delta.”
The current dominant strain, Omicron BA.2, has high secondary attack rates, meaning it is more likely than previous variants to jump from person-to-person.
4. Chance
“Finally, it might just be chance, based on how much virus the infected person has in their mouth, and how often (and how closely) others interact with them,” Prof Stanton said.
It is hard to believe that after two years, someone has had the luck to avoid Covid illness.
There are a number of factors that will play into their odds, however.
For example, someone who is able to work from home, lives alone and does their food shopping online may be less likely to have had Covid.
Whereas a frontline worker, such as in a shop, a care home or hospital, or someone who lives with a number of people, is much more likely to have had it.
5. Protection from vaccines
The large majority of people have now had a Covid vaccine (or two, or three, or four…).
This will alter immunity from one person to the next, as antibodies against Covid are highest around three weeks after a dose.
They start to weaken over the following months, hence why booster jabs are expected annually for the rest of time.
Andrew Freedman, an academic in infectious diseases at Cardiff University, told CNBC the reasons why some people get Covid and others don’t “presumably relates to immunity from vaccination, previous infection, or both”.
He added: “We know that many people have still caught (mostly mild) Omicron infection despite being full vaccinated, including [having had] a booster.
“However vaccination does still reduce the chance of catching Omicron and responses do vary from person to person. So some people catch it and others don’t despite very significant exposure.”
6. You’ve actually had it
Many people dumbfounded by the fact they’ve not had Covid often deduce that they have had it, but shown no symptoms.
Around a third of people with the virus do not seem to get tell-tale signs.
Testing helps to spot those that are “asymptomatic”.
However, there is also the notion that people have different viral loads, which contributes to how much virus they shed.
It appears that in people with low viral loads – where the virus has not replicated as dramatically in their body so they have fewer virus particles – PCR tests can give a false negative result.
People who are vaccinated are much more likely to produce low viral loads and milder symptoms if infected.
Investigations
The so-called “never Covid” cohort has spurred scientists on to conduct research.
Infectious disease specialists across the globe are looking at why some people’s bodies appear to be naturally protected.
Dr Rhia Kundu, first author of the Imperial study, said that “being exposed to the SARS-CoV-2 virus doesn’t always result in infection and we’ve been keen to understand why”.
However Dr Kundu also cautioned that no one should rely on the idea that they are super-immune to Covid, if they’ve yet to have it.
She said: “Instead the best way to protect yourself against Covid-19 is to be fully vaccinated, including getting your booster dose.”
Covid vaccines have been proven to reduce severe infections, hospitalisations, and deaths and remain largely effective against known variants of the virus.
Three doses have been shown to be the only effective way of preventing illness with Omicron stains.
However, vaccine immunity wanes over time, hence why older and more vulnerable adults are being told to come forward for a spring booster.
