If you thought losing your sense of taste and smell for a week or two over Christmas was bad, you’ve got to feel sorry for those with more lasting symptoms. Currently, more than a million people in the UK have long Covid – symptoms of coronavirus such as fatigue, headaches and a cough that last longer than three weeks.
But why do some people recover from Covid after just five days, while others suffer for weeks and months? A new study, published by the medical journal Cell, might have some answers.
The study took blood tests and nasal swabs from 209 patients who were infected with the coronavirus during 2020 and 2021. Researchers found four potential factors that could increase the risk of contracting long Covid: the presence of certain autoantibodies, viral load, reactivation of Epstein-Barr virus (a virus that usually infects young people and then becomes dormant) and Type-2 diabetes.
According to Dr James Heath, lead investigator of the study, among patients reporting three or more symptoms 95 per cent had one or more of these biological factors.
While the study’s findings are significant, some experts have questioned the limited observational period of 2-3 months and one pointed out that 71 per cent of the subjects had been hospitalised with Covid, which could skew the findings.
Nonetheless, research into what increases your risk of developing long Covid is growing all the time. Here are the major risk factors we know about:
A September 2021 report by the Office of National Statistics (ONS) showed that long Covid was most prevalent in adults who were 50 to 69 years old at both four weeks and 12 weeks after contracting the virus (19.1 per cent and 15.7 per cent respectively). Likewise, a longitudinal study from King’s College London found a 3.02 per cent rise per decade with age for Covid symptoms lasting four or more weeks.
“It’s very strongly associated with age – we’ve seen that in almost every study,” says Dr Claire Steves, clinical senior lecturer at King’s College London.
This could be due to changes in the immune system as one gets older, where it becomes “non-specially reactive so it’s less good at removing viruses and infections quickly”, says Dr Steves. As you get older, you are also more likely to have autoimmune conditions which, she adds, could make you more prone to long Covid.
2. Being a woman
Women are more likely to report long Covid symptoms at both four and 12 weeks after infection, according to ONS data. After 12 weeks, 13.4 per cent of women were still reporting symptoms compared to 9.8 per cent of men. Previous studies, including a study published in Nature journal and a separate study by Imperial College, had similar findings.
“There’s been a slight tendency towards female gender,” observes Amitava Banerjee, professor in clinical data science at University College London. Scientists don’t yet know why this is the case, he says. “There are hypotheses kicking around; is it to do with the oestrogen axis, is it hormonal? For some autoimmune conditions, there’s a female preponderance – we don’t know why.”
3. Poor mental health
Those with greater “psychological distress” before catching Covid are more likely to have symptoms after four or more weeks, according to the King’s College study.
“There are quite strong links between mental distress and your immune system,” Dr Steves explains. “For example, if you’re in mental distress then your immune system is potentially less responsive and reactive – your glucocorticoid system can be hyper-reactive and that leads you to be slightly immuno-suppressed.” This would impair your ability to fight infections.
There is a strong link between asthma and long Covid. A recent study published in the journal Nature found 94 per cent of individuals with a history of asthma bronchiale developed long Covid – that’s compared to 59 per cent who developed long Covid and did not have a history of asthma.
Other studies, including the King’s College longitudinal study, have also backed up these findings.
This could be because asthma is a respiratory disease – and Covid-19 enters via the respiratory system.
“Asthma ticks several boxes,” says Prof Banerjee. “You’ve got an autoimmune angle, you’ve also got the inflammation as well, as well as the shortness of breath and respiratory disturbance.”
5. Type 2 diabetes
In the study published in Cell, approximately a third of those with long Covid had type 2 diabetes. Researchers said this could be just one of several medical conditions that increases the risk of long Covid, which would become more apparent in a larger study sample.
This finding does not surprise Dr Steves. “We saw the suggestion of some signals, in our multi-cohort paper, with diabetes,” she says, referring to King’s College London’s longitudinal study. “So I wouldn’t be surprised if it comes out as a finding.”
6. The Epstein-Barr virus
Epstein-Barr is a virus that infects most people when they’re young (it is the virus that causes glandular fever) and then becomes dormant in their blood. The Cell journal article found a strong link between long Covid and patients who had traces of Epstein-Barr in their blood.
This does not surprise Dr Steves (who was not involved in the study). “The symptoms of Long Covid could be partly due to reactivation of other viruses,” she says.
7. Having several initial symptoms
If you have five or more symptoms in the first week of contracting Covid, you’re more likely to develop long Covid, according to Nature’s May 2021 study. It was the second-strongest predictor of long Covid (16.3 per cent). In the journal’s more recent study, those with more Covid-19 symptoms during primary infection were more likely to develop long Covid.
Likewise, symptoms of long Covid were between two and 6.5-fold more frequent in severe Covid-19 cases compared to mild cases (excluding those with loss of taste and smell), according to the same study.
This is to do with how the body responds to the virus. “If you’ve got a very active, quick-acting immune system, you knock it on the head quickly and you don’t get very many more symptoms […] whereas if you’ve got more symptoms, it’s gotten more into your body – that probably means it’s had an impact on your immune system in a different way,” says Dr Steves.
8. Viral load
The Cell article also found that a third of those presenting with long Covid symptoms had a higher level of coronavirus RNA in the blood early in the infection – also known as “viral load”.
This could explain why frontline workers are more likely to get long Covid, according to Prof Banerjee.
“Long Covid seems to be more common in healthcare workers and frontline workers, which tends to suggest that people who are in the firing line for higher concentrations of virus are more likely to have long-term consequences,” he says. However, he admits that these workers are also more likely to come into contact with the virus – and thus more likely to catch Covid in the first place, which could explain the higher proportions of long Covid.
The most influential factor in developing long Covid is the appearance of autoantibodies, according to the recent study in Cell. These autoantibodies are antibodies that mistakenly attack tissues in the body as they do, for instance, in auto-immune conditions like rheumatoid arthritis and lupus.
Autoantibodies were present in two-thirds of the cases of long Covid, according to Dr Heath.
Vaccines significantly reduce the risk
Being fully vaccinated could reduce your risk of long Covid, according to ONS data released this week. In a sample of UK adults aged 18 to 69 years, receiving two doses of a vaccine at least two weeks before contracting the virus was associated with a 41.1 per cent decrease in symptoms 12 weeks later.
Likewise, a previous study at The Lancet found that two vaccine doses approximately halved the odds of having symptoms for 28 days or more after infection.
“Vaccinations reduce the risk of long Covid,” adds Dr Steves.
It’s not entirely clear why but vaccines make the disease “less severe to start with”, Dr Steves says. “It’s also potentially primed the immune system to get on with its job”.
However, a vaccine won’t completely protect you from long Covid. “It reduces the risk but it doesn’t annihilate it,” she says.
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