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A systematic review suggests that at least a third of SARS-CoV-2 infections occur in people who never develop symptoms, providing strong evidence for the prevalence of asymptomatic infections.
The finding that nearly one in three infected people have no symptoms suggests that the tests should be changed, the researchers note.
“To reduce transmission from presymptomatic or asymptomatic people, we need to shift our focus from testing to home testing,” said lead author Daniel Oran, AM. Medscape Medical News. “Fast, inexpensive antigen testing, provided to millions of people for frequent use, could help us dramatically reduce the spread of the virus.”
The systematic review was published online on January 22 in Annals of Internal Medicine.
The findings come at a difficult time when the official number of COVID-19 cases in the United States exceeds 25 million for the first time. Public health officials have raised concerns over more transmissible, and possibly deadlier, variants of SARS-CoV-2, as a new presidential administration attempts to meet the challenge of improving distribution and vaccine acceptance rates.
The results also build on previous findings from the same research team – Oran and lead author Eric Topol, MD – who published a review article on asymptomatic cases of COVID-19. Although the initial data were more limited, they also suggested that a wider scope of testing is warranted, pointing out that asymptomatic individuals can transmit SARS-CoV-2 for up to 14 days. Topol is also editor-in-chief of Medscape.
In the current systematic review, the highest quality evidence comes from large studies in England and Spain. Nationally representative evidence included serological surveys of over 365,000 people in England and over 61,000 in Spain. When analyzed separately, approximately the same proportion of asymptomatic cases appeared: 32.4% in England and 33% in Spain.
“It was truly remarkable that national antibody screening studies in England and Spain – including hundreds of thousands of people – produced almost identical results: around a third of SARS-CoV-2 infections were completely asymptomatic, ”said researcher Oran. at the Scripps Research Translational Institute in La Jolla, California.
The systematic review included 43 studies with PCR testing for active SARS-CoV-2 infection and another 18 with antibody results indicating present or previous infection. The studies were published until November 17, 2020.
An assessment of asymptomatic transmission of SARS-CoV-2 infection has come a long way since the first referrals as to its significance, Topol noted via Twitter. “When Dr @camilla_rothe reported asymptomatic transmission a year ago, the @NEJM report was refuted and maligned. She was subsequently named TIME 100 Person of the Year.”
8. When Dr @camilla_rothe reported an asymptomatic transmission a year ago, the @NEJM report was refuted and disparaged. She was later named a TIME 100 Person of the Yearhttps://t.co/vSgQsx1qj8 pic.twitter.com/keNVF2misD
— Eric Topol (@EricTopol) January 24, 2021
Not symptomatic vs never symptomatic
The term “asymptomatic” could be misleading because some people in this group progress to develop signs of infection. This group of “presymptomatic” patients is probably a minority, the authors note. Longitudinal studies indicate that about three quarters of asymptomatic people with SARS-CoV-2 remain asymptomatic.
Topol predicted that the asymptomatic finding of a third party could draw commentary on the distinction between asymptomatic and presymptomatic individuals. He tweeted: “Some would say there is a mix with presymptomatic cases, but examination of all the data confirms this estimate to be conservative.”
5. Based on the totality of the data, we conclude that asymptomatic covid occurs in at least one-third of infections.
Some will argue that there is admixture with presymptomatic cases, but review of all the data supports this estimate as being a conservative one.— Eric Topol (@EricTopol) January 23, 2021
The heterogeneity of contexts, populations, and other study characteristics precluded the authors from performing a meta-analysis of the results.
Home is where is the test?
Based on their results, Oran and Topol believe that “COVID-19 control strategies must be modified, taking into account the prevalence and risk of transmission of asymptomatic SARS-CoV-2 infection”, they write. They suggest the frequent use of quick and inexpensive home tests to identify asymptomatic or presymptomatic people, as well as government-provided programs and housing to offer financial assistance and allow this group of people to self-isolate.
More research is needed to determine whether and to what extent SARS-CoV-2 vaccines prevent asymptomatic infection.
Topol and Oran have created a short video to highlight the results of their systematic review.
The study was funded by a grant from the National Institutes of Health.
Ann Intern Med. Published online January 22, 2021. Full text
Damian mcnamara is a stick Miami-based reporter. It covers a wide range of medical specialties, including infectious diseases, gastroenterology and intensive care. Follow Damian on Twitter: @MedReporter.
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