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‘Silent’ transmission: 2 in 5 people with COVID-19 have no symptoms

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Manish Saini
Manish works as a Journalist and writer at Revyuh.com. He has studied Political Science and graduated from Delhi University. He is a Political engineer, fascinated by politics, and traditional businesses. He is also attached to many NGO's in the country and helping poor children to get the basic education. Email: Manish (at) revyuh (dot) com

A global assessment that statistically pooled results from nearly a hundred studies involving over 29 million people discovered that 40.5% of those with confirmed COVID-19 did not exhibit any symptoms. Only 0.25 percent of those tested lacked symptoms, indicating that tests were only given to those who showed evidence of sickness.

People sick with COVID-19 can be infectious before they start to show symptoms, while some don’t show symptoms at all.

The new meta-analysis, published today, found that these presymptomatic and asymptomatic cases account for 40.50% and 0.25% of virus transmissions, respectively – meaning “silent disease transmission” can fuel outbreaks even if everyone who has symptoms is immediately isolated.

The disease induced by SARS-CoV-2, COVID-19, was initially identified in December 2019.  There have been 100, 455,529 confirmed cases worldwide as of January 28, 2021, with 2 166 440 deaths.  COVID-19 can cause a range of symptoms, including asymptomatic to mild respiratory infections, pneumonia, and even acute respiratory distress syndrome.

Asymptomatic infections were classified as patients who had no symptoms at the time of screening, which included infected people who had not yet acquired symptoms but would later develop symptoms (presymptomatic infections) and those who were infected but never developed any symptoms (true asymptomatic or covert infections).

Since these people have no symptoms, they will not seek medical attention and will not be recognized by temperature screening. Temperature screening will be less effective as a result of presymptomatic transmission. More asymptomatic infections could only be discovered via comprehensive testing and close contact tracing.

Unlike SARS, which had limited known transmission from asymptomatic individuals, data suggested that COVID-19 may be transmitted from asymptomatic people. 

A recent study found that asymptomatic patients’ upper respiratory virus levels were comparable to those of symptomatic patients. In the meantime, the maximum viral load in throat swabs at the time of symptom onset suggested that infectiousness peaked at or before the beginning of symptoms.

Asymptomatic infections may have also contributed to transmission within households, nursing homes, and clusters, according to studies.

Travel restrictions have been relaxed, and public areas have reopened, as the pandemic has been contained in many countries and regions.

As public life returns to normal, asymptomatic infections should be considered a source of COVID-19 infections, which play a significant role in the virus’s propagation within the population.

Asymptomatic carriers had to be managed in order to prevent cluster outbreaks and transmission within a community.

However, there is a lack of thorough data on the prevalence of asymptomatic infections in both the tested population and the confirmed COVID-19 population.

The current results from several studies differed significantly due to differences in study design and study population. As a result, they conducted a meta-analysis to better understand the global percentage of asymptomatic infections among the COVID-19 populations that had been tested and verified. 

The team followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines when doing the meta-analysis.

Asymptomatic people with positive SARS-CoV-2 test results (asymptomatic infections) were classified as those who did not have any symptoms when SARS-CoV-2 testing or diagnosis was performed.

Individuals with a confirmed COVID-19 diagnosis received a positive result for SARS-CoV-2 using a real-time reverse-transcription polymerase chain reaction assay on a throat swab or other specimen.

Using a database search and the reference lists of papers and reviews, the researchers found 2860 studies.
A total of 282 studies were subjected to full-text review.

The final analysis comprised 95 studies with information on the percentage of asymptomatic infections among the tested and confirmed populations.

A total of 29,776,306 people tested.

The pooled percentage of asymptomatic infections among the tested population was 0.25% (95% CI, 0.23%-0.27%), which was higher in nursing home residents or staff (4.52% [95% CI, 4.15%-4.89%]), air or cruise travelers (2.02% [95% CI, 1.66%-2.38%]), and pregnant women (2.34% [95% CI, 1.89%-2.78%]).

The pooled percentage of asymptomatic infections among the confirmed population was 40.50% (95% CI, 33.50%-47.50%), which was higher in pregnant women (54.11% [95% CI, 39.16%-69.05%]), air or cruise travelers (52.91% [95% CI, 36.08%-69.73%]), and nursing home residents or staff (47.53% [95% CI, 36.36%-58.70%]).

The pooled percentage of asymptomatic infections was 0.25% in the people who had been tested, and 40.50% in the people who had been confirmed to have COVID-19.

More asymptomatic infection screening is needed in communities, according to scientists, especially in locations where the virus has been successfully suppressed.

Source: 10.1001/jamanetworkopen.2021.37257

Image Credit: Getty

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