Back to Africa Check

No, asymptomatic Covid patients can transmit the virus, and masks work

A Facebook video posted on 5 July 2021 claims that studies show asymptomatic Covid-19 patients – people who don’t get sick – can’t transmit the new coronavirus. It also says the US Centers for Disease Control (CDC) published a review of studies and found wearing a mask doesn’t stop the spread of Covid.

In the video, a woman appears to be standing at a podium, talking to an audience off camera. She says: “Nearly 500 people were recently exposed to a Covid positive asymptomatic carrier. Zero got sick. Asymptomatic carriers of Covid do not spread disease.”

She goes on to claim: “The CDC a couple weeks ago did a study where they looked at every single other study in the entire world on face mask wearing and this is what they found. The CDC found, quote, ‘no reduction in viral transmission with the use of face masks’.”

The words “the information is there dont say u wernt warned” are printed on the video. It’s been shared more than 1,200 times so far, including in South Africa. 

Since Covid-19 was declared a pandemic in early 2020, the World Health Organization has warned that Covid patients who don’t show any symptoms of the disease can still spread it to others. 

It also says masks are a “key measure to suppress transmission and save lives”.

Do studies prove that asymptomatic Covid-19 patients can’t spread the disease? And has a CDC analysis found that masks don’t reduce transmission?


Video of US attorney Leigh Dundas

The video does not identify the woman, where she is, or when the video was taken. It’s poor quality, taken from an original that doesn’t appear to be online anymore.

But we did find a short video on Vimeo of a woman named Leigh Dundas, speaking on 13 April. Based on her voice, hairstyle, clothing and the background, it’s likely that the video on Facebook shows this woman, at the same event.

In the Vimeo video she identifies herself as a human rights attorney. The video is captioned “Leigh Dundas, Board of Supervisors, April 13 2021”. 

Dundas, a US attorney, publicly supports that country’s anti-vaccination movement. Voice of OC reports that, in May, she helped organise residents in California’s Orange county to go to local Board of Education meetings to petition against mandatory vaccinations and “vaccine passports”.

As Africa Check has found, there is no such thing as mandatory or “universal” vaccination in the US. And vaccine passports don’t exist there.

Asymptomatic patients can transmit the virus

In the Facebook video, Dundas refers to a May 2020 study in Wuhan, China. It’s titled A study on infectivity of asymptomatic SARS-CoV-2 carriers. The Covid-19 pandemic is thought to have started in Wuhan.

The researchers studied 455 people who had been in contact with asymptomatic Covid-positive patients. None of the 455 tested positive for Covid-19. 

But the study didn’t find that people with asymptomatic Covid-19 can’t transmit the virus. Instead, it concluded that “the infectivity of some asymptomatic SARS-CoV-2 carriers might be weak”. SARS-CoV-2 is the formal name of the new coronavirus that causes Covid-19.

Other studies of asymptomatic carriers have found that they can transmit the virus.

A January 2021 study looked at 2,250 people in a “confined” community of university staff in the Canadian province of Quebec. Confinement, the study says, is “used to reflect social restrictions instructed by Quebec's government”.

It found that 1.82% of the staff were asymptomatic carriers. None had contact with any known Covid patients. 

The researchers concluded: “Our results raise concerns about the possibility of viral spread through asymptomatic transmission.” But they added that the rate of asymptomatic transmission was unknown.

In February 2021, a study based on daily mass screenings of some 20,000 residents of Luxembourg, a small country in Europe, was published. It found that, on average, asymptomatic patients infected the same number of people as patients with Covid-19 symptoms. The researchers concluded: “Asymptomatic carriers represent a significant risk for transmission.”

CDC: Masks reduce Covid spread

And what about Dundas’s claim that a CDC analysis had found that masks didn’t reduce the amount of coronavirus transmitted between people?

This is not what the CDC website says. A science brief on the site, updated on 7 May 2021, quotes several studies that found face masks reduced the risk of Covid-19 infection by as much as 79%, and had led to declines in daily new cases.

The CDC concludes: “Experimental and epidemiological data support community masking to reduce the spread of SARS-CoV-2.” 

The CDC also says that making people wear masks can help prevent possible lockdowns in the future. The benefits increase when people are also required to use other measures against Covid: social distancing, hand washing and good ventilation. 

Conclusion: Video’s claims are false

In a video posted on Facebook, US anti-vaccination advocate and lawyer Leigh Dundas claims that asymptomatic Covid-19 patients can’t transmit the virus. She also says a study by the US Centers for Disease Control found that masks don’t reduce the spread of the disease.

But the CDC study doesn’t conclude that asymptomatic patients can’t transmit the virus. And  other studies have found that asymptomatic patients do transmit the virus. 

The CDC has published studies supporting the benefits of masks, and says wearing masks can reduce the spread of Covid-19.

Republish our content for free

We believe that everyone needs the facts.

You can republish the text of this article free of charge, both online and in print. However, we ask that you pay attention to these simple guidelines. In a nutshell:

1. Do not include images, as in most cases we do not own the copyright.

2. Please do not edit the article.

3. Make sure you credit "Africa Check" in the byline and don't forget to mention that the article was originally published on

For publishers: what to do if your post is rated false

A fact-checker has rated your Facebook or Instagram post as “false”, “altered”, “partly false” or “missing context”. This could have serious consequences. What do you do?

Click on our guide for the steps you should follow.

Publishers guide

Africa Check teams up with Facebook

Africa Check is a partner in Meta's third-party fact-checking programme to help stop the spread of false information on social media.

The content we rate as “false” will be downgraded on Facebook and Instagram. This means fewer people will see it.

You can also help identify false information on Facebook. This guide explains how.

Add new comment

Restricted HTML

  • Allowed HTML tags: <a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd> <h2 id> <h3 id> <h4 id> <h5 id> <h6 id>
  • Lines and paragraphs break automatically.
  • Web page addresses and email addresses turn into links automatically.
limit: 600 characters

Want to keep reading our fact-checks?

We will never charge you for verified, reliable information. Help us keep it that way by supporting our work.

Become a newsletter subscriber

Support independent fact-checking in Africa.