9th August, 20227 min read

Coronavirus reinfections: what’s the risk and why do they happen?

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If you’ve had

COVID-19
, you might think you won’t get it again. But unfortunately, as with other illnesses caused by viruses – such as colds and flu – you can get it more than once, and even multiple times.

This is known as ‘reinfection’. It means you’ve been infected by the coronavirus that causes COVID-19, recovered, then been infected again at a later date. And as we continue to live with coronavirus, reinfections are becoming increasingly common.

So what’s the risk of reinfection, why is it happening, and what part do virus ‘variants’ such as Omicron play? While we don’t have all the answers yet, read on to learn what the latest science tells us – including the best ways to help protect yourself from reinfection.

What’s the risk of getting COVID-19 more than once?

Earlier in the pandemic, coronavirus reinfections were rare. And research found that being infected gives you some level of protection against being infected again:

  • in 2020, a large, UK-wide study of health workers found that a previous infection was associated with an 84% lower risk of getting infected again
  • at the end of 2021, the evidence suggested that, for most people, the risk of reinfection was low for at least 5 to 6 months after a previous infection

But the virus has changed over time, with several new ‘variants’ appearing – and variants can increase the risk of reinfection. This is particularly true of the Omicron variants, the first of which appeared in South Africa in late 2021:

  • a large South African study published in March 2022 found that the risk of reinfection increased quickly after Omicron arrived – including the risk of getting infected for a third time
  • in the UK, figures from the Office For National Statistics (ONS) show a large increase in reinfection rates since the Omicron variants became the most common – with the risk of reinfection being about 7 times higher than when the Delta variant was dominant
  • as of 19 May 2022, more than 1 million reinfections had been recorded in the UK – at a rate of about 1 reinfection for every 17 first infections

Research also suggests that certain things can increase your risk of reinfection. The ONS found that, between July 2020 and June 2022, people were more likely to be reinfected if they:

  • hadn't had a
    COVID-19 vaccine
  • were younger
  • had a mild first infection
  • didn't have symptoms (were asymptomatic) when they were first infected

Why do reinfections happen?

Your risk of getting COVID-19 is reduced by both infection and vaccination, because they trigger your body to make infection-fighting proteins called ‘antibodies’. These are designed to attack infected cells and kill the virus. And after you’ve recovered, they stay in your body to form part of your protection (immunity) from future infections.

But you can be reinfected if your immunity stops being effective. This can happen for 2 main reasons:

Decreasing antibodies

Antibodies to the virus that causes COVID-19 can be found in the blood of people who have recovered from COVID-19, as well as people who have been vaccinated. While we don’t know exactly how long these antibodies last, evidence suggests that they may be present for at least 6 months after infection.

However, your level of antibodies will decrease over time. So even if antibodies are still present, there may be a point when they decrease below a level that provides effective protection against infection. This is known as the ‘threshold of protection’.

Virus mutations

When new variants of coronavirus appear, they have changes or ‘mutations’ that make them work differently to previous variants. This means your immune system might not be able to recognise and fight the virus, even if you’ve been infected before, and you can get infected again.

The Omicron variant has been found to be likely to avoid or ‘evade’ immunity from vaccination or a previous infection – which helps to explain the increase in reinfections seen in the UK since it became the dominant variant.

How soon can reinfection happen?

As mentioned above, it used to be thought that your risk of reinfection was low for at least 5 or 6 months after an infection.

But the virus variants have changed this, too. Because they can ‘evade’ your immunity from a previous infection, they can reinfect you sooner, before your COVID-19 antibodies have waned.

In a report published in April 2022, the US Centers for Disease Control and Prevention (CDC) looked at 10 people who were reinfected with the Omicron variant within 3 months of being infected with the Delta variant – the shortest time between infections was just 23 days.

What’s more, the new BA.4 and BA.5 Omicron ‘subvariants’ are thought to be particularly good at evading immunity, leading to reinfections happening sooner.

At the end of June 2022, Professor Tim Spector, who leads the Zoe Health Study in the UK, released a

video
in which he talked about reinfections and the BA.5 variant. “The numbers who got it again within the last 2 months is really, really small,” he says. “But the group that got it between 3 and 6 months is really growing… the number of reinfections is zooming up. This is what we’d expect with the BA.5 variant.”

Do reinfections cause milder illness?

Research from earlier in the pandemic suggests that if you get COVID-19 again, your symptoms are more likely to be mild – possibly because your immune system has been ‘primed’ by the previous infection and knows how to react.

In 1 study in Qatar from 2021, reinfections were found to be 90% less likely to lead to hospitalisation or death than primary infections. However, there have been cases of reinfection that caused serious illness and even death.

And new variants can also change how reinfections affect us. Research from the ONS suggests that people who are reinfected with the original (Alpha) variant are more likely to have a lower viral load – which can mean they’re less likely to get symptoms – than when first infected. But since the Omicron variants became dominant, there has been a large increase in reinfections with a high viral load.

So while there’s some evidence that reinfections and new variants may cause milder illness, there’s still a lot we don’t understand about COVID-19 – including what the long-term effects of repeated reinfections might be. So it’s important to continue to take steps to avoid infection or reinfection.

How to avoid infection or reinfection

1. Getting the COVID-19 vaccine – and any booster jabs – will give you the best protection against COVID-19. While it’s still possible to get COVID-19 after vaccination, the risks of getting infected, becoming very ill, needing hospital treatment or dying are all lower for vaccinated people than unvaccinated people.

2. You should follow the rules and guidelines in place where you live – but you can also take general steps to protect yourself and others. Whether or not you’ve had COVID-19 before, and even if you’re vaccinated, steps you can take include:

  • meeting people outside whenever possible
  • opening the doors and windows to let in fresh air when meeting people indoors
  • wearing a face covering in crowded indoor spaces, or where you can’t keep apart from others
  • limiting the number of people you meet and avoiding crowded places
  • regularly washing your hands with soap and water
  • using hand sanitiser when soap isn’t available
  • avoiding touching your eyes, nose and mouth when you haven’t washed your hands
  • avoiding anyone who has COVID-19 symptoms

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.