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COVID-19 - Incubation and Transmission

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COVID-19 - Incubation and Transmission

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People infected with the Coronavirus can spread the virus to others 2 to 3 days before they develop symptoms, and are highly contagious in the first couple of days. Read on to know more.

Written by

Dr. Lochana .k

Medically reviewed by

Dr. Shubadeep Debabrata Sinha

Published At February 16, 2022
Reviewed AtMarch 22, 2023


The reports of coronavirus started to spread across the world around December 2019, and it was known well by the world only in January. China reported that this was a new virus affecting mammals mainly. It was then identified to be the family of coronavirus that affects the respiratory system of the human body. It was later named the SARS-CoV-2. There are four different coronavirus categories: alpha, beta, delta, and gamma. Among them, only alpha and beta are found to infect humans. The previous coronavirus outbreak was known as a severe acute respiratory syndrome, the SARS, and the other one was MERS, the Middle East respiratory syndrome, which originated from Saudi Arabia.

Animals And Origin Of COVID 19:

The coronavirus outbreak was initially thought to be transmitted from an animal market at Wuhan from the meat of bats. It was linked with the previous outbreak of SARS and MERS, but still, the researchers are not able to find out a perfect solution.

Current State Of The CoronaVirus:

Since last December, the virus has crossed Wuhan almost all over the world. The WHO has declared it a pandemic. Due to a lack of initial awareness of the disease, and an easy transmission route, the virus tends to travel the world mainly due to the people who traveled around the world. The travelers act as the carrier of the virus. After that, it was found to affect the countries due to the incoming passengers from other countries. Almost all the leading countries went into lockdown, and many countries are still in lockdown as a completely enhanced community quarantine. Despite all the effective measures taken by the government and health practitioners, the curve of coronavirus infection is again peaking. Day by day, all the countries are experiencing more loss of lives. Currently, COVID-19 has infected about 80 lakhs people. The mortality rate is crossing more than four and a half lakhs people.

Incubation Period:

The incubation period is the time taken for the disease to express its symptoms. The incubation period of COVID-19 is approximately 14 days since the day of infection. The first 14 days are said to be the pre-symptomatic contagious period. In the second 14 days, patients are seen to express more severe symptoms. Once the virus has entered the body through the nasopharyngeal or oropharyngeal route, it starts to express its symptoms only by the fifth or sixth day. But, it has the capacity to spread the disease by day one itself. This is one of the notable points. This is the reason why isolating and treating coronavirus patients is difficult.

What Is the Incubation Period for Each COVID Variant?

According to a study published in 2022, the COVID-19 incubation period progressively decreased from the Alpha variant to the Omicron variant with the evolution of mutant strains. According to the findings of the research, the incubation period of COVID-19 caused by the Alpha variant was 5.00 days (95 % confidence interval [CI], 4.94 to 5.06 days), and the incubation period of COVID-19 caused by the Beta variant was 4.50 days (95 % CI, 1.83 to 7.17 days), both of which were comparable to the incubation period of the wild-type strain in Wuhan, China. (5.2 days).

Furthermore, the study found that the incubation period of COVID-19 caused by the Delta variant was 4.41 days (95 % CI, 3.7 to 5.05), which was shorter than the average incubation period of COVID-19 (6.26 days) and also shorter than the incubation periods caused by the Alpha variant and the Beta variant.

The result of that study showed that the Omicron variant of COVID-19 had an incubation period of 3.42 days (95% CI 2.88 to 3.96 days), which was shorter than the incubation periods of the Alpha, Beta, and Delta variants.

In addition, Infected children had a shorter mean incubation period (8.82 days; 95 % CI, 8.19 to 9.45) than the general population (6.65 days).

How Does the Transmission of Disease Occur?

There is still research going on to explain the exact spread from human to human transmission. It is found to affect the elderly and immunocompromised people very easily. The spread from animals to humans is still being traced. Since the virus mainly affects the respiratory system, the transmission was established to be from the nasopharyngeal secretions of the body. It could mainly include mucus and saliva. This type of infection is known as the droplet type of infection. The droplets are easily spread by spitting saliva or mucus, sneezing, and usage of things owned by infected people. It can also be transmitted due to poor social distancing. Later, after an increase in the number of cases, it was also proven that many affected individuals were asymptomatic. When they were incidentally checked, some people turned out to be positive. Thus, those individuals were termed as asymptomatic carriers of the disease.

What Are The Symptoms Of The Disease After Transmission?

The symptoms of the disease might range from being asymptomatic to a highly severe version of the disease. During the initial period of the disease, patients are known to stay asymptomatic, and later they might develop mild flu-like symptoms that include common cold, fever, headache, fatigue, and sore throat. Later, they may develop difficulty in breathing to a feeling of complete breathlessness. The degree of breathlessness can be mild to severe. Gastrointestinal symptoms like nausea and vomiting do not frequently occur in these patients. The nervous system might be affected in some patients. They might have symptoms of a stroke. It is one of the rare cases of COVID-19.

Droplet Infection:

There is a greater risk of transmission to the people who live close to the affected individuals. The droplets can be easily spread through the air to nearby places. The virus is also viable for at least 72 hours on contact surfaces of affected individuals. The respiratory mucus particles are highly virus-laden and competent enough to spread the disease. Larger droplets of infected particles stay in the air only for a less amount of time. The smaller particles are known to float in the air for a longer period of time. Significantly, coronavirus is known to live in aerosols and droplets for approximately 3 hours.

What Are The Transmission Stages?

The virus is prone to spread at a distance of at least six feet through the droplets dismissed in the air. When the person’s hand is contaminated by virus particles and if they touch their mouth or nose with the infected hand, the virus gets into the oropharynx or nasopharynx. It then starts to move slowly towards the respiratory system through the trachea and bronchus. COVID-19 is found to be a lower respiratory tract infection. So, from the bronchus, the virus moves to the lower respiratory tract towards the alveolus. Some studies have been established that coronavirus affects the angiotensin-converting enzyme receptors present there. It then enters the cells through the receptor and disintegrates its viral particles inside the cell.

What Are the Precautionary Measures?

Precautionary measures include practicing proper hygiene measures such as:

  1. Keep your things clean all the time.

  2. It is necessary to keep the working space also clean.

  3. Do not share your personal belongings.

  4. Soaps, towels, and other toiletries should not be shared with others.

  5. It is advised to have a separate food plate and drinking glasses.

  6. Maintain social distancing.

  7. Avoid going to public places.

  8. Consume foods that boost your immunity.


To conclude, one of the most important steps in choosing an isolation period is identifying the incubation period of various COVID variants. The spread of COVID-19 infection can be stopped only when people know how long they will be contagious and when healthcare providers know what the accurate isolation time is to prevent the spread of the disease.

Frequently Asked Questions


Is COVID-19 Infectious During the Incubation Period?

The incubation period of the COVID-19 virus may vary. The incubation period may last from two days to 14 days also. But during this period COVID-19 virus remains highly infectious and may spread to other persons.


What Is the Incubation Time for COVID-19?

The incubation period of the COVID-19 virus is variable. Usually, the symptoms appear within 3 to 4 days of the exposure. But sometimes, it may take 14 days for the symptoms to appear. In some cases, patients can be symptomless.


What Is the Incubation Period for Omicron Variant?

The incubation period of the omicron variant is two to three days. In usual cases, the incubation period of other COVID-19 variants is three to four days.


How Fast Does Omicron Spread?

The omicron variant can spread really fast compared to any other COVID-19 variant. Due to its structural complexities, omicron variants can multiply really fast and can escape the immune system. The incubation period for omicron is around two to three days, but this variant can spread even before the appearance of the symptoms.


Can You Get Infected by Omicron 4 Days After Exposure?

Yes, one can get infected by Omicron even 4 days after exposure. Though the incubation period of the Omicron variant is two to three days, in some cases, symptoms may also appear after this period. Even in some cases, the person may be asymptomatic. Usually, the person can wait for five days for symptoms to appear, and in high-risk cases, the person can wait another five days for any symptoms.


How Long Does It Take to Test Negative for Omicron?

Usually, it takes at least five days to test negative for the Omicron variant. If the person is asymptomatic or mildly symptomatic or symptoms are improving, the person can end his isolation after five days of a positive test.


What Is the Incubation Period for the BA5 Variant?

BA5 is a sub variant of the omicron. The incubation period of this variant is two to three days.


What Is the Incubation Period for Omicron According to CDC?

The incubation period for omicron is really short. According to the CDC (center for disease control), the incubation period is three to four days. According to some researchers, the incubation period may also be two days for the Omicron variant.


What Are the Accurate Rapid Tests for Omicron?

Rapid antigen and antibody test kits can be used for the Omicron variant. However, the success rate of such tests for the identification of Omicron is limited. Polymerase chain reaction (PCR) tests should always be done to detect the Omicron variant.


Do Rapid Tests Detect Omicron?

Yes, rapid antigen-antibody tests can be used to detect Omicron. But the chances of false negative results in such cases are really high. Confirmatory tests can be done using a polymerase chain reaction test.


What Is the Quarantine Period for Omicron?

If the person is mildly symptomatic or asymptomatic or his symptoms are improving the quarantine period for Omicron is five days. If symptoms persist the quarantine period can be extended to 10 days also.


Are You Still Contagious if You Test Negative?

A person who has tested negative for COVID-19 can not be contentious. However, test results from rapid antigen and antibody tests can be ambiguous. Only the polymerase chain reaction test is the most authentic test.


How Do I Know What COVID Strain I Have?

It's very difficult to understand the strain of the COVID-19 virus. The symptoms of COVID-19 infections from different strains are similar. So, only an epigenetic study of the samples can be used to identify the strain. But certain rare symptoms like ulcers in the mouth, skin rashes, and muscle pain can be linked to the Omicron variant.


When Will the COVID Test Negative?

The negative COVID test will only be if the person is cured of COVID infection or the person has not been infected. Test results from the rapid tests can be ambiguous. That is why confirmatory tests should always be done using a polymerase chain reaction method.
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Dr. Shubadeep Debabrata Sinha
Dr. Shubadeep Debabrata Sinha

Infectious Diseases


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