Jan. 24 is the one-year anniversary of an important but largely unnoticed event in the history of the Covid-19 pandemic: the first published report of an individual infected with the new coronavirus who never developed symptoms. This early confirmation of asymptomatic infection must have sounded alarm bells and changed our response to the storm. But it did not. A year later, we are still paying the price for this catastrophic mistake.
At least one in three people infected with SARS-CoV-2, the virus that causes Covid-19, does not develop symptoms. This is the conclusion of a review we just published in the Annals of Internal Medicine. It summarizes the results of 61 studies involving more than 1.8 million people.
But during much of the pandemic, fierce resistance – and even outright denial – the recognition of this not-so-typical disease pattern has led to ineffective testing practices that could have driven the pandemic out of control.
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On 28 January 2020, Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases, said: ‘In the history of respiratory viruses of any kind, asymptomatic transmission has never been the cause of outbreaks. … Even if there is a rare asymptomatic person who can transmit, an epidemic is not driven by asymptomatic carriers. ‘
This was a general view. On June 8, 2020, a senior official of the World Health Organization called asymptomatic transmission ‘very rare’.
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To his credit, Fauci was among those who immediately criticized this remark. Based on epidemiological data available since his earlier comments, he said it was “incorrect” to describe asymptomatic transmission as rare.
When we published a report of 16 cohorts with a significant amount of asymptomatic infection in June and suggested that it may play a role in the progress of the pandemic, several researchers wrote letters to the editor demanding that our article be withdrawn. word.
The best evidence currently suggests that about half of Covid-19 cases are caused by infected people who have no symptoms when they transmit the virus. This asymptomatic distribution is roughly divided between those who later develop symptoms known as pre-symptomatic individuals, and those who never develop symptoms.
Although the importance of asymptomatic infection in understanding Covid-19 has been surprising to some, infectious disease experts have long known that asymptomatic infection is common in many diseases. More than 90% of people infected with poliovirus have no symptoms. It is estimated that approximately 75% of influenza infections are asymptomatic. Yet these important precedents are largely ignored.
Asymptomatic coronavirus infection is not necessarily benign. Several studies have reported abnormal lung scans in those without symptoms, as well as myocarditis, a type of heart inflammation. The long-term implications for the health of asymptomatic infection are not known.
Although knowledge about asymptomatic infection has developed strongly, the tactics to combat the pandemic are not. It is now obvious that testing only those with symptoms, as was common early in the pandemic, is a mistake because it ignores the invisible legions of infected people who have no symptoms. But it is not enough to just increase the number of tests. The problem is that current testing practices are incapable of detecting and containing asymptomatic infection.
Virtually all coronavirus tests performed in the US search for the genetic material of the virus using the polymerase chain reaction (PCR). It requires expensive equipment and trained technicians. Results are usually returned days – sometimes even weeks – to the test. This means that people learn that they are infected with SARS-CoV-2 long after they may have transmitted the virus to others. Tests are more about accounting – to measure the number of infected infections – than to contain the spread of the virus.
What is needed is a pivot point for another type of testing. Antigen tests, which look for a bit of coronavirus protein, cost only a few dollars each and can yield results within minutes. Like home pregnancy tests, they require minimal instructions. Antigen tests are ideal for detecting people who are contagious, rather than those who are long past the contagious phase of Covid-19, or who have such low levels of the virus that they are unlikely to infect others.
Cheap quick home tests help infected people to isolate themselves before they can spread the virus. Regular testing – at least a few times a week – is essential, as evidenced by successful testing efforts at some universities, which have enabled students to return to campus. A new focus on self-tests, combined with financial assistance and perhaps even temporary housing for isolation, will directly address the problem of asymptomatic infection.
The roll-out of Covid-19 vaccines carries the risk of a new wave of asymptomatic infections. The two vaccines approved by the Food and Drug Administration have been shown to prevent disease, but not asymptomatic. Even after vaccination, the coronavirus can still temporarily enter the airways of the airways, making it possible to infect others. Preliminary results from one vaccine trial seem encouraging, with an apparent two-thirds reduction in asymptomatic infection after the first dose. But many other studies are underway.
There is no time machine that allows us to go back to January 24, 2020 and make the plans we had to make, which would recognize the importance of asymptomatic infection. But it is not yet too late to recognize the mistake and aggressively go to the practices of the test to end the pandemic.
Daniel P. Oran is a member of the Digital Medicine Group at Scripps Research Translational Institute, of which Eric J. Topol is founder and director.