Study: People Without COVID-19 Symptoms Are Less Likely to Spread the Virus

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Verywell Health / Theresa Chiechi

Key Takeaways

  • People with no COVID-19 symptoms during infection may be less likely to spread the virus, according a new research.
  • Another study also suggested that people who developed COVID infections were more likely to be asymptomatic if they were exposed to an asymptomatic case
  • Asymptomatic carriers can still pass along the virus, meaning testing, masking, and isolating are still important to limit the spread.

New research suggests that people without COVID-19 symptoms are much less likely to transmit the virus than those who display symptoms.

In mathematical modeling studies, estimated proportions of all COVID-19 infections that resulted from asymptomatic individuals were mostly below 15%, according to researchers at the University of Bern in Switzerland.

The researchers evaluated 30 studies and data on more than 28,000 people who were infected with COVID-19 from 42 countries. Nearly 12,000 people had asymptomatic infections.

There's no clear answer as to why people with no COVID symptoms are less likely to spread the virus. One theory is that asymptomatic people may produce less infectious droplets, the authors said.

A 2021 study in China also suggested that people were more likely to develop an asymptomatic COVID-19 infection if they were exposed to an asymptomatic case. Yang Ge, PhD, an epidemiologist at the University of Georgia, and the lead author of the study, told Verywell that asymptomatic cases may be due to a lesser amount of virus shedding.

“However, even assuming the asymptomatic cases shed less, if they have high social activities, then the transmission still could be high," Ge said.

Another study found that people with asymptomatic COVID have an elevated white blood cell count—a sign of better immune function—compared to symptomatic people.

Genetics may also play a role. Research has suggested that some patients have variations of the ACE2 genes that make them more susceptible to getting infected by the spike protein on the COVID-19 virus, which could cause more severe symptoms.

Asymptomatic vs. Presymptomatic

Experts stress that asymptomatic infections are not the same as the presymptomatic phase of COVID-19.

Before people exhibit symptoms or test positive for the coronavirus, they're considered “presymptomatic” and can still pass the virus on to others—even if they don’t yet realize they are sick.

“In our review, people with presymptomatic infection were as likely to transmit the infection to close contacts as those who had symptoms at the time of diagnosis,” the researchers of the new study told Verywell via an email. “And people without any symptoms throughout the course of infection can still pass it on."

That is why health experts recommend testing after a potential COVID exposure and isolating if you're infected. Even if you don't feel sick, it doesn't mean you're not infectious at all.

What This Means For You

People infected with COVID but who have no symptoms are less likely to pass on the virus than people with symptoms. That being said, it's still important to test yourself for COVID if you've had exposure and isolate if you suspect you are positive or test positive.

Getting vaccinated and booster is also key to reducing COVID severity. Even if you’ve already had a prior infection, vaccination may lower the risk of developing long COVID.

Researchers at the University of Bern said there are still gaps in their knowledge about how well vaccines can prevent COVID-19 transmission, especially with newer variants that are more adept at evading immune responses.

“We are working on a new update to find the proportion of asymptomatic infection in people infected with variants of concern and amongst people who have been vaccinated," they said.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Buitrago-Garcia D, Ipekci AM, Heron L, et al. Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: Update of a living systematic review and meta-analysis. PLoS Med. 19(5). doi:10.1371/journal.pmed.1003987

  2. Ge Y, Martinez L, Sun S, et al. COVID-19 transmission dynamics among close contacts of index patients with COVID-19: A population-based cohort study in Zhejiang Province, China. JAMA Intern Med. 2021;181(10):1343–1350. doi:10.1001/jamainternmed.2021.4686

  3. Han H, Xu Z, Cheng X, et al. Descriptive, retrospective study of the clinical characteristics of asymptomatic COVID-19 patients. Rosenberg HF, ed. mSphere. 2020;5(5). doi:10.1128//msphere/5/5/mSphere922-20

  4. Lippi G, Lavie C. J, Henry B. M, et al. Do genetic polymorphisms in angiotensin converting enzyme 2 (ACE2) gene play a role in coronavirus disease 2019 (COVID-19)?Clinical Chemistry and Laboratory Medicine. 2020;58(9):1415-1422. doi:10.1515/cclm-2020-0727

By Laura Hensley
Laura Hensley is an award-winning lifestyle journalist who has worked in some of the largest newsrooms in Canada.