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Covid contagion: incubation time, before symptoms?

Even in the summer of 2022, Covid-19 remains a highly contagious disease. The initial Sars-CoV-2 virus infected 3 people, the Delta variant more than 6, the Omicron variant almost 10 and its BA5 sub-variant is even more contagious. Period of contagion, before and after symptoms, asymptomatic…

Appeared in China in December 2019, the Covid-19 disease had infected more than a million people worldwide at the beginning of April 2020, proof of the high contagiousness of his virus, the SARS-CoV-2. The coronavirus transmission capacity Sars-CoV-2 is evaluated through the measurement of “R0”. This “R” corresponds to the reproduction rate of the virus and indicates the number of people infected by a positive case of Covid-19. The higher it is, the more the disease is transmitted. The release of variantsfirst theAlpha came from England then the Delta came from India and the Omicron from South Africa changed the game because they were much more contagious than the original Sars-Cov-2 strain of 2020. The sub-variant BA.5 of Omicron majority in France since mid-June is more contagious than BA.2, itself already more transmissible than Omicron’s BA1 sublineage what “shows the evolutionary capacity of the virus capable of evading vaccines, at the same time as increasing its transmission” explained infectious disease specialist Anne-Claude Crémieux on FranceInfo on June 22. At the end of July, the 7th wave descends with a reproduction rate of the virus which falls below the threshold of 1 (a contaminated person infects less than another). Public Health France also reports a increase in the proportion of Covid reinfections since December 2021. how many days are you contagious when you are positive for Covid? 5 days ? 10 days is the time of isolation? Are we contagious if there are no symptoms ? During the incubation period? Focus on knowledge.

Effective reproduction rate of the Covid virus in France as of July 23, 2022 © Gouvernement.fr

What is the definition of the term “contagion”?

The word “contagion” comes from the Latin “cum” which means “with” and “tangere” to “touch”. In medical language, contagion is defined by the transmission of an infectious agent and, where applicable, the corresponding disease, from an infected subject to a healthy individual, by direct contact (skin, mucous membrane) or indirect (airborne transmission (saliva , postillions…), digestive…).

The Sars-CoV-2 virus spreads mainly by case of close contact with an infected personby small liquid particles expelled through the mouth Where through the nose if the infected person coughs, sneezes, speaks or take a deep breath. “You can also contract Covid-19 when the virus enters the mouth, nose or eyesa more likely situation when people are in direct or close contact (less than one meter away) with an infected person” says the WHO. You can also be contaminated if we touch our eyes, nose or mouth before washing your hands, after touching a contaminated surface. The transmission of the virus is increased in indoor spacescrowded and insufficiently ventilated.

Duration: what is the Covid contagion time?

The contagious phase of a Covid-19 positive patient is initially 8 days on average and starts about 2 days before symptoms start. With the Omicron variant, “replication is fasterconfirmed Professor Alain Fisher at the head of the Vaccine Strategy Council for France, to Les Echos. So, everything gets shorter, including the symptomatic – or asymptomatic phase but contagious.

According the study by Japanese researchers published in January 2022, it is unlikely that vaccinated Omicron cases will shed infectious virus 10 days after diagnosis or the appearance of their symptoms (as was the case with the original virus, editor’s note). The amount of viral RNA (or “viral load“) was highest 3-6 days after diagnosis (test) or 3 to 6 days after onset of symptomsthen gradually decreased over time. We would be like this contagious for a shorter time (6 days compared to ten) and not necessarily before the onset of symptoms with the Omicron variant.

How contagious is the Omicron variant?

The Omicron variant became the majority in France at the end of 2021 in just a few weeks. The number of infections was doubling every 2-3 days in late November-early December, much faster than when the Delta spread. According to studies reported by French Public Health, “Omicron is about 3 times more transmissible than Delta”. “A professor of medicine in the United Kingdom claims that, without barrier measures, the R0, the reproduction rate would be close to 10“informed epidemiologist Éric d’Ortenzio of Inserm on TV5Monde, on December 31. His incubation period is also shorter: “Replication is faster, confirmed Professor Alain Fisher at the head of the Vaccine Strategy Council for France, to Les Echos. So, everything gets shorter, including the symptomatic – or asymptomatic phase but contagious.” According a Japanese study published in January 2022, the viral load is high 3-6 days after Omicron diagnosis (test) or the onset of its symptoms. The majority Omicron sub-variant BA.2 in France until the beginning of June was “more contagious than its predecessor” (BA1) had indicated Professor Arnaud Fontanet on France Inter on March 14. About 30% what’s more. And the subvariant BA5 now majority”spreads better than BA.2″ what “shows the evolutionary capacity of the virus capable of evading vaccines, at the same time as increasing its transmission” explained infectious disease specialist Anne-Claude Crémieux on FranceInfo on June 22.

What is the incubation period for Covid?

Incubation covers the period between contamination by the virus and the appearance of the first symptoms. The median incubation period for Covid-19 is initially 5 days but has been reduced with Omicron. As Professor Yazdan Yazdanpanah of the Scientific Council explained on BFM-TV on January 2, 2022,we are in front of a variant which has a duration (incubation, editor’s note), before the onset of symptoms, which went from 5 to 3 days”. We can thus be in contact with the virus and have the first signs of contamination three days later. During this period, the person can be contagious.

Viral load peaks in the first week of illness.

How long are you contagious before the onset of symptoms of Covid-19?

“According to laboratory data, it is mainly just before infected people develop symptoms (i.e. two days before the appearance of symptoms) and at the very beginning of the disease that they are the most contagious” has explained the World Health Organization at the start of the coronavirus epidemic in 2022. Today, faced with the variant Omicronresearch has not shown that people are contagious before their diagnosis (test) or their symptoms but rather during the first week. A British meta-analysis bringing together 79 studies on Sars-CoV-2 (5340 people) published on November 19, 2020 in the scientific journal The Lancet had already shown that the viral load of the Sars-CoV-2 coronavirus in the upper respiratory tract peaked during the first week of illness.

How long are you contagious after the onset of Covid symptoms?

After the 5th day, the viral load decreases.

According to the English authors of the study of Lancet published in November 2020, the contagiousness peak of a Covid-19 positive person runs until the 5the day after onset of symptoms. Afterwards, the viral load decreases. According to Japanese analyzes of January 2022 on cases Omicronthis viral load would be maximum 3 to 6 days after diagnosis or onset of symptoms then would decrease. The authors also considered that it was unlikely that vaccinated Omicron cases will shed infectious virus 10 days after diagnosis or the appearance of their symptoms”. The contagion is therefore particularly strong in the first week following the onset of symptoms. The WHO also informs that “People who develop a severe form disease can be contagious longer”.

Are you contagious when you don’t have symptoms of Covid (asymptomatic)?

A person infected with the Sars-CoV-2 virus but who has no symptoms is contagious and can infect other people. Similarly, someone who never develops symptoms can also transmit the virus even though “it is not yet clear to what extent this is happening” says the WHO. Note that if asymptomatic cases are contagious, “Covid-19 transmission occurs mainly from people with symptoms” indicates the agency.

What is the risk of having the Covid 2 times or more?

Public Health France reports on July 7 a increase in the proportion of Covid reinfections since December 2021, rate of the diffusion of the Omicron variant (12% of confirmed COVID-19 cases in week 23 (June 6-12, 2022) were possible cases of reinfection). A high number of reinfections with Omicron after a first infection with this same variant is observed. Nevertheless, the probability that a reinfection occurs after a first infection by another variant (Alpha, Delta or other) is even higher. “The probability of reinfection increases with the age of the first infection to reach a shelf about 6 months after the first infection”.

A contact case is a person who has been in contact without protective measures (such as a type 1 mask) with a Covid-positive person. The longer and closer the contact, the greater the risk of contamination (more than 15 minutes, less than two meters)underlines the Ministry of Health. A contact person must be tested on D+2.

Sources:

The SARS-CoV-2 variant, Omicron, shows rapid replication in human primary nasal epithelial cultures and efficiently uses the endosomal route of entry. Thomas P. Peacock1. Department of Infectious Disease, Imperial College London, UK, W2 1PG

Recommendations relating to the vaccination strategy. Senate press conference Thursday, July 1, 2021.

Covid-19 – Get vaccinated? Decide with your doctor. January 29, 2021. HAS

Vaccination against Covid-19: transparency, pragmatism and flexibility are the keys to an effective campaign. Press release. November 9, 2020. HAS.

Rapid responses in the context of Covid-19 – First-line care of patients suspected of Covid-19. Validated by the College on June 18, 2020. Updated on November 5, 2020. HAS.

How is COVID-19 transmitted? July 9, 2020. WHO.

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