Infectious Diseases Data Verified

Asymptomatic COVID-19

Published on Jun 24, 2020 and last reviewed on Jul 04, 2020   -  4 min read


A COVID-19 positive person who does not show any symptoms of the disease is called asymptomatic. Read the article to know more about asymptomatic COVID-19.

Asymptomatic COVID-19

The most debated topic surrounding COVID-19 (the Coronavirus disease) pandemic is how rapidly and easily this virus seems to spread. 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 new 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 new 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 cloth face-covering in public and to maintain social distancing.

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 a 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 so far 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. Until recently, it was believed that such patients do not spread the virus. But recent studies have shown contradicting reports.

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 an Argentine cruise ship had no symptoms of COVID-19. In Karnataka, India, out of the 753 positive patients, 574 patients (76 %) have been asymptomatic.

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.’


With so much uncertainty surrounding this virus, it is important to follow instructions from medical agencies on preventing the spread through quarantines and social distancing. As so many studies show the possibility of asymptomatic patients to be contagious, it is not possible to determine the exact number of infected people at a given time, which makes preventive measures the only and best option to be safe.

Even if an asymptomatic person talks, coughs, or sneezes, the virus becomes airborne and can infect you. Maintain at least 6 feet distance from others and avoid going to crowded places. The CDC has recommended wearing a face-covering made of cloth in places where social distancing cannot be maintained. This also helps prevent asymptomatic patients from spreading the virus unknowingly. Avoid using N95 or surgical masks if you do not have upper respiratory tract infection symptoms, as there is a global shortage of personal protective kits. Make sure these masks are reserved for healthcare workers, who need them more.

Article Resources

Last reviewed at:
04 Jul 2020  -  4 min read




Comprehensive Medical Second Opinion.Submit your Case

Related Questions & Answers

COVID-19 - Home Isolation and Quarantine

Article Overview: To prevent the spread of COVID-19, suspected and infected patients are kept away from others. Read the article to know about quarantine and isolation. Read Article

Dr. Sneha Kannan
Dr. Sneha Kannan
Infectious Diseases Specialist

The WHO (World Health Organization) declared the COVID-19 outbreak as a public health emergency of international concern. All countries are advised to detect COVID-19 cases early, isolate such cases, manage their symptoms, trace their contacts, and to prevent the spread of SARS-CoV-2, which is the v...  Read Article

COVID-19 - How Long Can SARS-CoV-2 (Coronavirus) Survive on Surfaces and Air?

Article Overview: New studies have shown that the new Coronavirus can survive for hours to days on various surfaces. Read the article to find out if you can get infected by touching such surfaces Read Article

Dr. Sneha Kannan
Dr. Sneha Kannan
Infectious Diseases Specialist

A new coronavirus resulting in pneumonia-like symptoms began making the headlines in late 2019. Since it first emerged in China, this virus has spread to almost all countries in the world and has resulted in the death of thousands of humans. The virus was later named SARS-CoV-2, (Severe Acute Respir...  Read Article

Homeschooling - Tips for Parents

Article Overview: Homeschooling is becoming common as a result of school closures due to the COVID-19 pandemic lockdown. Many parents are struggling to come to terms with this new way of teaching their children. This article will discuss some advice and strategies to support parents in teaching their children at home. Read Article

Dr. Suresh Kumar G D
Dr. Suresh Kumar G D

What Is Homeschooling? Homeschooling is a type of learning where the child is predominantly educated at home instead of sending them to a regular school. Homeschooling is a new experience for many families; it is one of the unexpected developments parents are grappling with as a result of the COVID...  Read Article

Popular Articles Most Popular Articles

Do you have a question on Covid-19 or Covid-19 Pandemic?

Ask a Doctor Online

* guaranteed answer within 4 hours.

Disclaimer: No content published on this website is intended to be a substitute for professional medical diagnosis, advice or treatment by a trained physician. Seek advice from your physician or other qualified healthcare providers with questions you may have regarding your symptoms and medical condition for a complete medical diagnosis. Do not delay or disregard seeking professional medical advice because of something you have read on this website.