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When’s best to take a PCR test? COVID incubation times and isolation guidelines explained.

When’s best to take a PCR test? COVID incubation times and isolation guidelines explained.

As of the date of publishing (28/06/2022), the UK Government no longer requires self-isolation after travel or once you have tested positive for COVID-19. However, it is a recommended course of action if you have tested positive. Here’s our guide of what to do when testing for COVID:

When is the best time to take a COVID test?

Studies have reported that the highest coronavirus viral load (the total amount of virus a person has inside them during infection) is seen in the throat and nasal passage when your symptoms begin to show.

So if you have one or more of the following, it’s recommended to take a COVID test if you are able to:

  • New continuous cough
  • High temperature
  • Loss of – or change in – your normal sense of taste or smell (anosmia).

This time of early symptoms is not only the best time to test if you think you might have the virus.

Why is it best to test when you’re beginning to show symptoms?

The reason the onset of early symptoms is such a good time to test is because it’s when the virus is showing in very high quantities in the nose and throat. So if you swab at this point, there’s a higher chance of collecting viral particles on the swab successfully which improves the likelihood of detecting its presence in the laboratory using a molecular testing kit.

What to do if you are positive?

Earlier, the Government mandated 10 days of self-isolation. This is because it typically takes this duration to go from infected to no longer testing positive for the disease. Some people actually test positive for longer – some shorter – but this seems to be the average. This 10-day rule applies even if you don’t have symptoms.

Now, it is recommended that you try to self-isolate for 5 days and avoid contact with high-risk people for 10 days.

What is all this based on?

It comes down to what we understand about how COVID progresses. So far, the science indicates that the virus passes through two stages:

Incubation period – 4-5 days

Symptomatic period – 5-15 days

What is the incubation period?

This is the time when you might have COVID, but you don’t realise it yet. You feel normal, but if you have been exposed to the virus and your immune system hasn’t fought off the attack, it is multiplying in your body. In these early days, it’s more difficult to diagnose – though not impossible, when you choose the most sensitive tests such as molecular PCR test. The incubation period seems to last around 5 days.

What is the symptomatic period?

The symptomatic period is when you start to show symptoms – until those symptoms have gone and you are no longer infectious. This period can last from 5-15 days, though as your infection progresses, you will show less and less virus when you get tested (the ‘viral load’ is lower). However, this doesn’t necessarily mean that you are less infectious – it’s just that the virus is harder to spot.

So when are people most infectious?

It’s less about ‘infectiousness’ and more about how we behave when we might be contagious. So far, it has been estimated that nearly 50% of COVID-19 infections have been passed on from people who were in the incubation phase – when ‘presymptomatic’. This means they did not have symptoms at the point they passed the virus on to others, and were out and about behaving normally.

This is what makes the virus very efficient at spreading; people are less likely to know they are infected at the point where they are feeling healthy, out in public and possibly spreading it to others unwittingly.

When is the best time to test before visiting loved ones?

In an ideal world, you would isolate for a full 14 days, then test to be 100% sure that you’re COVID clear. But being realistic, isolating for 5 days – to allow any virus you might have picked up to incubate – is a good option before testing.

Is it worth testing if you don’t isolate?

Though you won’t be as sure that you’re COVID free, it is worth testing even without an isolation period if you choose a high sensitivity test, such as molecular PCR. These tests are analysed in a unique way that means even the tiniest traces of the virus’s genetic material can be detected – so you’re less likely to get a ‘false negative’. Read more about different types of tests here (insert link).

Should I get tested if I have no COVID-19 symptoms?

Even if you do not develop any COVID-19 symptoms at all, you may still be infected and pass the virus on to others without knowing it. This is called asymptomatic COVID. That’s why – if you want to visit someone vulnerable – it can be a good idea to isolate and take a private COVID test.

What can I do if I don’t want to get tested?

Whatever your circumstances, it’s really important to follow local guidelines, and the national advice:

  • Wash hands – regularly with soap or use sanitiser
  • Cover face – with a mask that you change regularly
  • Make space – 2 metres where possible

It’s also a good idea to meet outside if you’re allowed to do so, and to be mindful that all family members (however small!) should regularly sanitise or wash hands. Staggering festive meetings to give time for any symptoms to show is also sensible if feasible.

REFERENCES:,smell%20 (anosmia).