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How to tell if you've already had coronavirus without realising

Photo credit: Getty Images
Photo credit: Getty Images

While we all hoped the coronavirus pandemic might just be a difficult couple of months in 2020, the virus proved to be in it for the long haul and in the UK, we welcomed the arrival of 2021 with news of another lockdown. Now, four months later, we're steadily working our way out of it, and hope to be rid of our social distancing rules by 21 June. But despite some sense of normality being within reach (largely thanks to the vaccine roll out), it's still hard to think of anything but COVID right now.

For many who have already been struck down by the virus, they're clear on exactly when they had it and how long it lasted. But others might not be so sure. We know it's possible that some people can contract COVID-19 without realising - in fact, around 17%-20% of cases are estimated to be asymptomatic - so if you're wondering whether you might fall into this group, how can you tell? Here’s everything you need to know, including how the COVID vaccination might be able to inform you whether you've had the virus previously or not.

Have you had coronavirus without realising?

You could very possibly already have had coronavirus. Dr Dominic Pimenta, a cardiologist based in London who founded HEROES to provide wellbeing and financial support to NHS workers, tells Cosmopolitan: "We are all aware of the typical symptoms of COVID (high fever, dry cough) but many patients have very mild or no symptoms at all. When symptoms do occur, fever and cough are present in around 50% and 60% patients, respectively.”

Aside from the key symptoms we all know so well, there are some other signs that you may not have recognised as indicators of coronavirus. Such as:

You had recurring headaches

70% of people suffer headaches with coronavirus, according to Dr Pimenta - but it’s not one of the most talked-about symptoms. If you're the type to suffer regularly with headaches, you may not have thought anything of them - but that's not to say they weren't a signal that something else was going on.

You felt tired

If you felt like an entire week had been wiped out due to tiredness, it could have been a sign of COVID. Around 63% of people diagnosed report fatigue as a symptom.

You had a sore throat

A sore throat could easily pass as a cold, or even being a bit run-down - but it actually could be a sign that you have coronavirus. In fact, 52.9% of sufferers have a sore throat, so don't immediately disregard it.

You had vomiting and diarrhoea

It's not talked about as a symptom, but stomach pains, sickness and diarrhoea could be signs of coronavirus, although rarely on their own - only four percent of people were diagnosed with theses as a sole condition.

Other common symptoms are:

Can the vaccine reveal if you've had COVID before?

We're now well into the vaccine roll-out in the UK, and while none of the vaccines on offer (Pfizer, AstraZeneca and Moderna) can explicitly confirm whether or not you've had a previous case of the virus, research suggests they may inadvertently be able to provide a clue. In one recent study into vaccine side effects, carried out by the National Institute for Health Research in conjunction with the ZOE COVID Symptom Study app, experts concluded that "individuals vaccinated with a single dose of [the vaccine] were more likely to report systemic [side] effects if they had a previous SARS-CoV-2 positive test, than were those without known past infection. Local effects were similarly higher in individuals previously infected than in those without known past infection."

What it suggests is if you react to your vaccine with systemic side effects (which are symptoms that affect the wider body) or with local side effects (symptoms local to the area where the jab was given, so in this case the arm), you are more likely to have had a previous case of COVID. Common systemic side effects of the vaccine include fatigue and headache, while the most widely reported local side effect of the coronavirus vaccine is a sore arm.

Photo credit: Vladimir Mandic - Getty Images
Photo credit: Vladimir Mandic - Getty Images

How do antibody tests work?

There is a more firm way to increase your chance of knowing whether you've been infected in the past: by taking an antibody test.

"When you become infected with any virus your body fights back with two different systems," Dr Pimenta explains. "The first is the 'innate' immune system, and is like a shotgun, ready to attack a new pathogen straight away but in a very blunt, scattershot fashion. Meanwhile, the body kicks in the 'acquired' immune system, which is a slower but a targeted, sniper-like attack, built specifically to the invading bug, through antibodies.

Photo credit: Yulia Reznikov - Getty Images
Photo credit: Yulia Reznikov - Getty Images

"Once established, these antibodies stick around, although they take up to a month to reach peak levels after infection.

"The antibody test looks for reaction to these antibodies, by showing them bits of the virus on a plate and assessing whether they stick. We can measure how much of these antibodies stick and that gives us an idea of the number of antibodies. Unfortunately, these antibodies can sometimes disappear again after several months, so it's unclear how useful these tests are to the public at this point in time.

Getting hold of an antibody test isn't easy, either. Free antibody tests have only really been available for certain people who work in primary care, social care or education - or for those involved in health studies. You can test privately, but it's important to make sure you go through a system such as BUPA so you can be sure it's legitimate.

What about a lateral flow test?

Rather than focussing on whether you might have had coronavirus in the past, it's better to focus on the here and now. If you have symptoms, sign up to take an NHS coronavirus test in your nearest area. You'll get the results back within a day or two and should take steps to isolate before getting your results just to be on the safe side.

Alternatively, lateral flow testing is now freely available for everyone in the UK, which allow you to undergo a test and get the results back within the hour. You can get hold of one either via collecting a box from certain pharmacies, by requesting them to be delivered to your home, or by visiting a local testing site (find out exactly how to get them via all the different options here).

Photo credit: georgeclerk - Getty Images
Photo credit: georgeclerk - Getty Images

It's worth noting, however, that the lateral flow tests are designed to detect people who are asymptomatic and so you should only take this test if you are not displaying COVID symptoms. Otherwise, you need to do a lab-analysed PCR test which you can request from the NHS online.

In the meantime, let's all carry on sticking to the rules that remain in place, get our vaccines when we're offered them, and hope that we really are nearing the end of the worst of the pandemic.


The information in this story is accurate as of the publication date. While we are attempting to keep our content as up-to-date as possible, the situation surrounding the coronavirus pandemic continues to develop rapidly, so it's possible that some information and recommendations may have changed since publishing. For any concerns and latest advice, visit the World Health Organisation. If you're in the UK, the National Health Service can also provide useful information and support, while US users can contact the Center for Disease Control and Prevention.


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