JThe. 24 marks the one-year anniversary of an important event, but largely unnoticed 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 an asymptomatic infection should have triggered the alarm and profoundly altered our response to the approaching storm. But that did not happen. A year later, we are still paying the price for this catastrophic error.
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 with more than 1.8 million people.
But during much of the pandemic, fierce resistance – and even total denial – to recognizing this not-so-typical disease pattern led to ineffective testing practices that allowed the pandemic to get out of hand.
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On January 28, 2020, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said: “In the entire history of respiratory transmission 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 caused by asymptomatic carriers. “
This was a widely accepted view. On 8 June 2020, a senior official at the World Health Organization called asymptomatic transmission “very rare”.
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To his credit, Fauci was one of those who immediately criticized this comment. Based on epidemiological data that has become available since his previous comments, he said it was “not correct” to characterize asymptomatic transmission as rare.
In June, when we published a report of 16 cohorts with considerable proportions of asymptomatic infection and suggested that it could play a role in the progression of the pandemic, several researchers wrote letters to the editor demanding that our article be retracted.
Today, the best evidence suggests that about half of Covid-19 cases are caused by infected people who have no symptoms when transmitting the virus. These symptom-free disseminators are roughly divided between those who develop symptoms later, known as pre-symptomatic individuals, and those who never develop symptoms.
While the importance of asymptomatic infection in understanding Covid-19 has been surprising to some, infectious disease specialists have known for a long time that infection without symptoms is common in many diseases. More than 90% of people infected with poliovirus have no symptoms. And about 75% of influenza infections were estimated to be asymptomatic. However, these important precedents were largely ignored.
Asymptomatic coronavirus infection is not necessarily benign. Several studies have reported abnormal lung scans in infected people without symptoms, as well as myocarditis, a type of inflammation of the heart. The long-term health implications of asymptomatic infection are not known.
Although knowledge about asymptomatic infection has evolved a lot, tactics to combat the pandemic have not evolved. It is now obvious that testing only those with symptoms, as was common in the beginning of the pandemic, is a mistake because it ignores the invisible legions of infected people who have no symptoms. But just increasing the number of tests is not enough. The problem is that current testing practices are not adequate to detect and contain asymptomatic infections.
Virtually all coronavirus tests performed in the United States look for the virus’s genetic material through the polymerase chain reaction (PCR). Requires expensive equipment and trained technicians. Results are usually returned days – sometimes even weeks – after the test. This means that people learn that they have been infected with SARS-CoV-2 long after they have passed the virus on to others. The tests involve more accounting – calculating the number of infections detected – than containing the spread of the virus.
What is needed is a pivot for a different type of test. Antigen tests, which look for some of the coronavirus protein, cost just a few dollars each and can produce results in minutes. Like home pregnancy tests, they require a minimum of instruction. Antigen tests are ideal for detecting infectious people, rather than people who have passed the Covid-19 infectious stage or who harbor so low levels of the virus that they are unlikely to infect others.
Fast and inexpensive home tests would help infected people isolate themselves before they can spread the virus. Frequent tests – at least several times a week – are essential, as demonstrated by the successful testing efforts at some universities, which have allowed students to return to campus. A new focus on self-testing, in combination with financial assistance and perhaps even temporary isolation accommodation, would directly address the problem of asymptomatic infection.
The launch of Covid-19 vaccines carries the risk of a new wave of asymptomatic infections. The two vaccines authorized by the Food and Drug Administration have been proven to prevent disease, but not asymptomatic infections. Even after vaccination, the coronavirus can still take temporary residence in the lining of the respiratory tract, making it possible to infect others. Preliminary results from a vaccine trial appear encouraging, with an apparent two-third reduction in asymptomatic infection after the first dose. But many other studies are underway.
There is no time machine that would allow us to go back to January 24, 2020 and make the plans that we should have made, that would have recognized the importance of asymptomatic infection. But it is not too late to acknowledge the blunder and to move aggressively towards testing practices that will help end the pandemic.
Daniel P. Oran is a member of the digital medicine group at the Scripps Research Translational Institute, of which Eric J. Topol is founder and director.