Why are you Covid-free?

It was St Patrick’s Day and Wellington’s J J Murphy bar was pumping with a live band, and staff were struggling to stop the crowd from dancing. A tipsy stranger planted a kiss on my cheek. I headed home, sure I was going to wake next day with a corona hangover. But no.

In the past couple of months I have been to numerous parties and dinners, squeezed into a crowded spa pool, shared drinks and hugs. So far so good.

We passed one million confirmed cases of Covid-19 last week, and the vast majority of them were added in the past three months as Omicron swept the nation. The real infection count may be 2-4 million. That leaves plenty of us still free of the virus. So what made us the lucky ones?

Some of us have actually had it, but not shown any symptoms, which is really the dream scenario aside from the fact you could have infected others while you were asymptomatic.

Most of us were vaccinated, social-distancing, mask-wearing and hand-washing, which formed crucial defences. Many just got lucky, skirting our invisible foe, oblivious to the danger we faced.

But some people were in the thick of it, living with a sick spouse or children, or working closely with Covid patients. How did they sail through?

A study published in January found that people who had come into contact with the virus but not been infected, had high levels of T cells in their bodies, which they amassed from previous coronavirus infections in the form of the common cold. T-cells are part of our immune system and help the body fight infection.

When it comes to our genetic makeup, there is a historic precedent that may help us find an answer. A small number of humans have natural immunity to HIV, the virus that causes AIDS, as well as malaria, norovirus and some other infectious diseases. Studies are seeking to discover if some of us are literally built to fend off a SARS-CoV-2 infection.

A major paper published in the journal Nature last year identified 13 genetic markers that seem to play a role in how susceptible we are to Covid, or how severely it affects us.

The genetic information of 50,000 Covid-19 patients was compared with that of healthy volunteers obtained from blood banks and clinical studies. One genetic marker scientists identified is DPP9, a gene linked to lung cancer and pulmonary fibrosis. Researchers believe the role those genes play could be as influential on how susceptible we are to Covid as the effects of obesity or diabetes, raising the prospect of developing treatments to suppress or ‘‘silence’’ specific genes we know are associated with this virus and future ones. That’s still some way off.

In the meantime, don’t assume your genes have saved you. There is plenty of scope for a nasty surprise, courtesy of Covid.