When it comes to other illnesses, we might know what 'asymptomatic' means but in terms of Covid-19 and the impact of asymptomatic people, we might need to re-think.
Now one year into the pandemic, scientists know more about coronavirus than they ever have done before - from the early warning signs of Covid-19 to look out for to the particular symptoms of Covid-19 in children (opens in new tab). Being able to identify those who have the virus, alongside the various lockdowns we've had since last year, has played a huge part in reducing transmission.
But what about those people who aren't diagnosed with the virus because they never get a test? Before lateral flow tests (opens in new tab) became widespread, the only reason to get a standard PCR coronavirus test was if you had symptoms. With no cough, fever, shortness of breath or loss of taste or smell, people were likely (and are still likely) to think they're healthy and go about their days as normal.
This is where asymptomatic Covid-19 becomes a serious problem.
What does asymptomatic mean in terms of Covid-19?
Being asymptomatic means having Covid-19 but not showing any symptoms at all.
The first evidence of asymptomatic virus transmission was first reported by the Scientific Advisory Group for Emergencies (SAGE) in late January. They warned the government of the emerging coronavirus pandemic and said, "There is limited evidence of asymptomatic transmission, but early indications imply some is occurring.” Two weeks later, SAGE confirmed that a better testing system for travellers would be needed in the UK to understand the prevalence of these asymptomatic cases of Covid-19.
In his most recent public address to mark one year since the first lockdown, Prime Minister Boris Johnson called the reluctance to react to asymptomatic Covid-19 cases as one of his biggest regrets of the pandemic. He said, “I think in retrospect, there are probably many things that we wish that we’d known and many things that we wish we’d done differently at the time, because we were fighting a novel disease under very different circumstances than any previous government had ever imagined,
“Perhaps the single biggest false assumption that we made was about the potential for asymptomatic transmission, and that did govern a lot of policy in the early days. All that misunderstanding about the reality of asymptomatic transmission certainly led to real problems that [meant] we then really had to work very hard to make up ground.”
While the government were made aware of asymptomatic Covid-19 in January, the general public weren't told about this way of spreading Covid-19 until March 2020 - after the lockdown was announced.
Later in April 2020, the Centers for Disease, Control and Prevention (CDC) in the US released research which advised any asymptomatic carriers of Covid-19 to self-isolate to prevent spreading the virus. It was pointed out at this time, however, that this relied on asymptomatic people being tested. While we have lateral flow tests which do this now, there was no system for it at the time.
Can asymptomatic patients transmit Covid-19?
Asymptomatic patients were recently called (opens in new tab) the 'hidden drivers of the pandemic' as they can transmit Covid-19 without being aware they had it at all.
The study also confirms that not only can asymptomatic patients transmit Covid-19, but it’s one of the most significant ways that coronavirus is spreading around the world.
In fact the study, published in September, concluded that the frequency and highly infectious nature of asymptomatic people are the main reasons why Covid-19 turned from an epidemic (concentrated in one area) to a pandemic (a global spread). It also says that evidence points to the need for strict test and tracing systems of all known coronavirus contacts, regardless of symptoms, to prevent further spreading of the virus.
This means that if the NHS contract tracing app (opens in new tab) flashes up with a warning sign or those who’ve submitted their details are contacted by test and trace, it’s essential that they self-isolate.
It’s also why wearing masks in all indoor public spaces where social distancing can’t be maintained is essential. Coronavirus is spread through droplets in the air so by covering the mouth and nose with a mask, the infectious droplets are less likely to spread to others.
How many people with coronavirus disease are asymptomatic?
The most reliable research suggests that 1 in 3 cases of Covid-19 are asymptomatic, but there is conflicting research on this subject as it's difficult to identify asymptomatic Covid-19 cases.
Nevertheless, Matt Hancock highlighted the need for asymptomatic testing in January this year. He said, "With roughly a third of people who have coronavirus not showing symptoms, targeted asymptomatic testing and subsequent isolation is highly effective in breaking chains of transmission. Rapid, regular testing is led by local authorities who design programmes based on their in-depth knowledge of the local populations, so testing can have the greatest impact.
"We are now expanding this offer to every local authority across the country, and asking testing to be targeted on workers who cannot work from home during this national lockdown, while asking employers to work with us to scale up workforce testing.
"Lateral flow tests have already been hugely successful in finding positive cases quickly – and every positive case found is helping to stop the spread - so I encourage employers and workers to take this offer up. We must all do all we can to stop the spread of COVID, right now."
The research found that one out of every 5 people in London and the South East of England who have had coronavirus did not show any symptoms. It was also discovered that 27% of people who did feel unwell did not display the three main signs of coronavirus, which are a new and continuous cough, a fever and a loss of taste and smell. However, another study that was conducted in Italy (opens in new tab) back in July showed that over 40% of all coronavirus cases were asymptomatic. So there’s really no knowing how many people with coronavirus are asymptomatic.
Is there testing available for asymptomatic people?
Due to cases of the South African and Brazil variants around the UK, asymptomatic testing has been made available in most areas around the country.
These are lateral flow tests, which detect any active Covid-19 infection in the body. They are available to order online for the whole household if one person within the household attends school, college or university, whether working or studying there. They have also been made available to anyone who cannot work from home during the third lockdown, including those working in supermarkets and other essential shops.