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Asymptomatic COVID-19

Published on Jun 24, 2020 and last reviewed on May 18, 2022   -  4 min read


Asymptomatic COVID poses a huge challenge in controlling the transmission of the disease, especially due to vaccination. Read this article to get an insight into asymptomatic COVID-19.

Asymptomatic COVID-19


At the beginning of this pandemic, most countries focused on only testing and isolating people and contacts who showed upper respiratory tract infection symptoms. Many people who came in contact with infected patients were not tested as they had no symptoms. They were asked to stay in quarantine for 10 to 14 days, and if they did not develop any symptoms, they were not tested.

However, several studies show that infected people with no or mild symptoms can still potentially spread the coronavirus. From anywhere between 25 and 80% of COVID-19 patients are unaware that they are infected, as they either exhibit no or mild symptoms.

What Does It Mean to Be Asymptomatic?

Asymptomatic means that you are infected with a microorganism, but have never exhibited any disease symptoms. In COVID-19, the common symptoms include dry cough, loss of taste or smell, fever, muscle aches, diarrhea, and breathing problems. Being asymptomatic or symptom-free does not mean that it is safe for you to come in contact with others or avoid isolation, as asymptomatic patients are also contagious.

Why Is COVID-19 Spreading So Rapidly?

The incubation period of the coronavirus, which is the time for the virus to cause symptoms, is 2 to 14 days. Many infected patients might be healthy and asymptomatic for up to two weeks or show mild symptoms like fever, cough, diarrhea, and headaches, which mimics the flu or a cold. Early in the outbreak, these factors made many people not realize that they might be carrying the virus, which resulted in the rapid spread of the virus.

On top of this, many asymptomatic people with positive contact or travel history are not getting themselves tested, or they are not following strict quarantine procedures, which worsens the situation. This is why doctors and government officials are urging people to wear face masks in public and maintain social distance.

What Are the Routes of Transmission From COVID-19 Patients?

The following are the routes of transmission of SARS-CoV-2 (the virus that causes COVID-19) from an infected person:

  1. Symptomatic Transmission - An infected person with signs and symptoms of COVID-19 is known to be symptomatic COVID-19 patient. When such a patient spreads the virus to others, it is called symptomatic transmission. This was believed to be the primary mode of transmission. Evidence suggests that the shedding of SARS-CoV-2 is highest in the first three days since the onset of symptoms.

  2. Pre-symptomatic Transmission - It takes an average of 5 to 6 days for an infected person to show symptoms (can be up to 14 days). Until an infected person shows signs and symptoms, he or she is said to be a pre-symptomatic patient. Data collected show that some individuals can be tested positive 1 to 3 days before the development of symptoms. A study claimed patients to be most contagious during this period.

  3. Asymptomatic Transmission - An infected person with no symptoms of COVID-19 is called an asymptomatic patient. Initially, it was believed that such patients do not spread the virus. But studies have shown contradicting reports. Individuals who show no symptoms after being affected with SARS-CoV-2 have the ability to transmit the virus for longer than 14 days. It transmits the virus for an extended period as compared to asymptomatic individuals.

What Proportion of People Are Asymptomatic?

Data from various studies show that around 25 to 80 % of people who have COVID-19 are asymptomatic and have no idea that they are spreading the infection. This was first confirmed by the Centers for Disease Control and Prevention (CDC) in March 2020. After this, many researchers have reported cases of SARS-CoV-2 positive patients who had no symptoms. Researchers in Singapore were successful in identifying 7 clusters of cases, where pre-symptomatic transmission is the only logical answer for the occurrence of secondary COVID-19 cases.

In Iceland, 43 out of 100 patients of coronavirus had no symptoms. In Italy, 30 of 73 patients (around 40 %) did not have symptoms during the first round of testing, and around 44 % did not have symptoms during the second round. Two studies in May 2020 also suggested that the majority of people with COVID-19 might be without symptoms.

331 out of the 712 (around 46 %) infected passengers and crew on the Diamond Princess cruise ship were without symptoms. And 104 out of 128 infected people on board of an Argentine cruise ship had no symptoms of COVID-19.

Why Are Some Patients Asymptomatic?

According to a new study published in the journal Nature Medicine, a weaker immune response to the new coronavirus is said to be the reason for some patients with COVID-19 to show no symptoms. This study highlights the risks of ‘immunity passports,’ a risk-free certificate to show that the patient has recovered, and it is safe for him or her to travel and go to work. This study analyzed 37 asymptomatic patients, who were tested positive for SARS-CoV-2.

The viral shedding, which is when the virus leaves the host cell after replicating successfully, in these patients was 19 days on average, as compared to 14 days in patients with symptoms. This study also found that during the acute phase of infection, the antibodies produced to fight off this virus (IgG) were much lower in asymptomatic patients than symptomatic patients.

It was also noted that the level of antibodies reduced more than 80 % in asymptomatic patients in 8 weeks, compared to 62 % in symptomatic patients. These observations have made scientists believe that asymptomatic patients might have a weaker immune response to this new virus. This raised doubts about the possibility of reinfection in patients with reduced levels of antibodies and the use of ‘immunity passports.’

What Are the Risks of Asymptomatic COVID-19?

Increased asymptomatic cases indicate the greater potential of the virus to have a silent and deep spread between human populations.

Being asymptomatic does not mean there are no harmful effects associated with the infection. Computed tomography (CT) should be used to determine any subclinical changes in the lungs and increased research is needed on this aspect.

What Are the Preventive Measures Against Asymptomatic COVID-19?

Even if an asymptomatic person talks, coughs, or sneezes, the virus becomes airborne and can infect you. First and foremost, two regular doses of COVID vaccine followed by booster doses should be taken from time-to-time. Maintain at least 6 feet distance from others and avoid going to crowded places. A face mask should be worn at all times while going out. Wash your hands frequently with soap and water. This also helps prevent asymptomatic patients from spreading the virus unknowingly.

Also, steps should be taken by the government to broaden the testing in people who do not exhibit any symptoms of COVID-19.


With so much uncertainty surrounding this virus, it is important to follow instructions from medical agencies on preventing the spread through vaccination, quarantines and social distancing. Asymptomatic COVID-19 transmission can only be prevented by strictly following adequate prophylactic measures since we are not aware of who would transmit the virus to stay away from them.

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Last reviewed at:
18 May 2022  -  4 min read




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