The communication nor-mally arrives via text or email. Just as you’ve taken off your coat at work, or put on your coat to meet a friend for dinner, a message will flash up on your phone…‘So sorry...’

Someone’s ill again. Floored by a tummy bug / nasty cold / chesty cough / raging flu. And while you do your level best to be sympathetic, isn’t it always the same people who seem to catch every bug going?

For me, the apologies for absence always spark a slight pang of jealousy.

‘There is a gene mutation that is present in around one in 400 of the population that is thought to protect against influenza,’ says Professor Openshaw (file photo)

Convulsion-inducing high fevers and hospital dashes aside, there’s something distinctly comforting and indulgent about a genuine ‘sickie’: The duvet hauled down from the bed upstairs. Hot water bottles. Hot blackcurrant. Heinz tomato soup and Lucozade. Flannelette pyjamas. Old re-runs of Columbo and Murder, She Wrote on TV.

No wonder sick leave costs British employers £29 billion each year, with workers taking an average 9.1 days each, the highest rate in the world, and nearly double that in the U.S.

Yet, I genuinely struggle to remember the last time I was among them.

I’ve never experienced full-blown influenza — the odd cold, yes, but nothing that’s confined me to bed — and I’ve never had a flu vaccination.

As an adult, I’ve been prescribed antibiotics probably half a dozen times, and most of them have been dental infections caused by injuries I sustained in a car accident years ago.

Viruses seem to bounce off me, and I travel on the Tube every day, with people literally sneezing and coughing in my face.

The theory is the bigger or more sociable a family is, the more bacteria and viruses you come into contact with at a young age and the more resilient your immune system is as a result (file photo)

As young things, my husband John and I travelled around Asia together. John was a vegetarian at the time, and very careful about what he ate.

I, meanwhile, with the gung-ho arrogance of youth, devoured everything going. Anyone for a dodgy, unidentified dead thing on a stick served by a street vendor followed by an abundance of unwashed fruit?

But guess which one of us ended up with an appalling dose of food poisoning? His, not terribly romantic phrase for me, after that holiday was ‘Teflon guts’.

Often having a strong immune response to one illness or infection will have a pay back — being less robust in the face of another infection

My children, Lois, who’s 19, and Joe, 16, seem to be heading in the same direction. They regularly got awards for 100 per cent attendance at school. Apart from a nasty bout of glandular fever when she was 12, Lois has never experienced anything worse than a sniffle.

You’re probably irritated by me at this point, and expect me to launch into a chia seed and kale inspired sermon on how I’m reaping the rewards for clean eating, but honestly, I’m no Gwynnie.

I drink too much. I definitely eat too much, and have an appalling habit of cadging cigarettes when tipsy.

The only good thing I do is exercise, I run 10k two or three times a week, swim and practise yoga at weekends, and walk half an hour every day to and from the train station.

Yet viruses and bacteria attack indiscriminately, and we all catch them the same way. They don’t care if we’re in running gear or size-20 velour lounge pants. All they need is a moist surface on which to latch and they invade.

An example often quoted is that the genes that helped some of those in Ireland survive the hardships and diseases of the potato famine are the same that increase the risk of cystic fibrosis — which is why that country has among the highest rates of the disease in the world (file photo)

The common cold, for example, is spread when droplets containing microscropic bugs known as rhinoviruses (there are up to 200 different strains of these) are transferred between humans when an infected person sneezes or blows their nose.

They attach themselves to the nasal lining and invade the blood stream, injecting their genetic material into host cells, reproducing, then bursting out of the cell, killing it.

The immune system goes into emergency mode, sending out ‘killer’ white blood cells to engulf and obliterate the virus, raising the temperature of the body in the process to create a more hostile environment for it, and inhibit its spread.

Bacteria are spread in much the same way, but, unlike viruses, can be treated with antibiotics. They are responsible for infections ranging from tonsillitis to tuberculosis.

There will be some unlucky souls who don’t smoke, who exercise and do all the right things and still get ill (file photo)

So what explanation do the experts give for viruses and bacteria not ‘getting’ certain people? I have a nasal lining like everyone else. Or could it be that the viruses do get me, but my killer cells deal with them before I’ve had a chance to plug in the kettle for my first Lemsip? Probably the latter, it would seem.

Certainly ‘super immunity’ is a subject that fascinates immunologists: ‘We all recognise that there are some people who drift from illness to illness while there are others who never seem to catch a thing,’ says Dr Nick Beeching, a consultant in infectious diseases at the Royal Liverpool University Hospital.

‘The tricky thing is pinning down why certain people are this way.’

Certainly there is a lengthy list of things that can impact on how likely you are to catch an infection.

This includes everything from how often you wash your hands (in my case, not very often) to if you mix with young children, who invariably pick up every bug going (not any more) to the medication you take: antacids make people more vulnerable to stomach infections for example (I don’t take them).

It could even go back to childhood. The theory is the bigger or more sociable a family is, the more bacteria and viruses you come into contact with at a young age and the more resilient your immune system is as a result.

Here, I think Dr Beeching may have struck a chord. My mother was the nurse at the local doctors’ surgery, where she came into daily contact with all manner of horrible bugs, all of which she brought home, and never got ill herself.

She was also of hardy, farming stock who thought antibiotics were for wimps, hence my sister and I were left to fight off all but the most severe illnesses without medical intervention. Frame of mind can influence your chance of getting ill, too, say experts.

For it seems how well your immune system functions can even depend on whether you are a glass half-full or glass half-empty type.

‘If your psyche is good — if you are in a positive state of mind — then that does seem to help,’ says Dr Beeching.

'For it seems how well your immune system functions can even depend on whether you are a glass half-full or glass half-empty type,' writes Julia Lawrence (file photo)

‘People who are often stressed and feel run down by that stress are more likely to get ill. It’s possible that is because it has an effect on the endocrine system, i.e. how our hormones, such as the stress hormone cortisol, behave.’

Here, the argument doesn’t stack up for me, for I have a very stressful job and consider myself a natural born pessimist. Yet Professor Peter Openshaw, president of the British Society for Immunology, argues that in some cases, stress can actually bolster defences.

If your psyche is good — if you are in a positive state of mind — then that does seem to help

‘There was a study done with dental students in the run up to exams that found that the immune system could be rather empowered by a certain amount of stress for a short amount of time — but after the exams they crashed.’

But as our moods can come and go, the most likely explanation for my life-long good health is that I was born with lucky genes.

‘We are increasingly recognising that genetics are involved in the efficiency of the immune system — and some people are, in effect, pre-programmed to fend off illness better than others,’ says Dr Beeching.

The fact that I can fight off tummy bugs as well as colds means I must have especially lucky genes, according to Professor Openshaw.

Yet scientists are only just starting to unravel the true impact genetics have on our immune system.

‘Over the past five years we have been trying to identify certain genes in the digestive tract that help regulate the surface lining of the gut — as these are thought to be very important in fighting infections there,’ adds Dr Beeching,

We are increasingly recognising that genetics are involved in the efficiency of the immune system — and some people are, in effect, pre-programmed to fend off illness better than others (file photo)

Meanwhile, there is a whole different set of genes said to protect us from flu. ‘There is a gene mutation that is present in around one in 400 of the population that is thought to protect against influenza,’ says Professor Openshaw.

The gene controls a protein that defends the body against infection by crowding around cells, making it harder for the flu virus to penetrate.

‘When we did a study of people in hospital with severe influenza we found only six per cent of those patients had this gene,’ adds Professor Openshaw.

So it sounds very likely that I am a fortunate carrier, and have passed the gene onto my children. But even ‘lucky genes’ can have their drawbacks.

People who are often stressed and feel run down by that stress are more likely to get ill

‘Often having a strong immune response to one illness or infection will have a pay back — being less robust in the face of another infection,’ says Professor Openshaw.

An example often quoted is that the genes that helped some of those in Ireland survive the hardships and diseases of the potato famine are the same that increase the risk of cystic fibrosis — which is why that country has among the highest rates of the disease in the world.

Aside from genes, the other thing that could be going in my favour is the fact that I exercise.

‘There are all sorts of changes — short and long term — to the immune system that can be brought about through exercise,’ adds Professor Openshaw.

‘Even if you go for a run around the park you can bring about a moderate improvement in the number of white cells — or killer cells that are circulating in your blood.’

‘Being inactive and being obese have all been found to have an adverse effect on the immune system’ adds Dr Beeching.

There is a whole different set of genes said to protect us from flu (file photo)

And happily, experts play down the impact that diet has on our immunity. ‘It’s a tempting idea that single nutrients can improve your immunity but the evidence for this is a little weak,’ says Professor Openshaw.

‘Yes, if you are actually deficient in certain nutrients — and living on burgers and chips — then your diet is unlikely to provide the full range of nutrients you need.

'But if you eat the basic essentials of a balanced diet most of the time then that is likely to be adequate for the needs of your immune system.’

Yet there will be some unlucky souls who don’t smoke, who exercise and do all the right things and still get ill.

‘As an infectious diseases specialist, I get referred people who have, for example, recurrent tonsillitis and often I can find no good reason why this is happening to them,’ adds Dr Beeching.

‘We check for any severe immune deficiencies and in the vast majority of cases can find nothing to explain why this individual is getting ill — clearly there may be subtle things playing a part that we have yet to identify.’

Could tempting fate be one of them? As I write, I am picturing the viruses and bacteria lining up, desperate to teach me a lesson and wipe the smug look off my peachy, healthy face.

The irony is just too tempting. Maybe I’ll get my duvet day after all.