what have the Omicron variants changed?

“How long can you remain contagious if you are positive for a variant of Omicron? † The question is put to us by Isabelle. Since the outbreak of Covid-19, we have been asked regularly about the duration of contagiousness. Just like the symptoms. While the epidemic continues in our country, West France Make the point.

Which variant or sub-variant became the majority?

In the latest epidemiological update, Public Health France reports an incidence of 898 per 100,000 inhabitants for the week of April 14 to 24, 2022. That is a decrease of 26% compared to the previous week. “The slowdown in the circulation of SARS-CoV-2 has been confirmed in the national territory with a decrease in all virological indicators”, notes Public Health France. However, we are not done with Covid-19 yet. “The indicators remain high”, France Public Health Note.

On November 28, there were 59,760 new cases in France; 66,700 averaged over the previous seven days. Far from the 5,000 cases recorded on average per day in October before the Omicron wave ignited our immune responses.

Currently, it is the BA.2 subvariant of Omicron that continues to circulate. According to Public Health France, it was responsible for 99% of Covid cases.

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What incubation period?

The incubation period, the time between infection and the appearance of the first symptoms, is being scrutinized by scientists. Before the Omicron, the latter agreed to an incubation period of five days. Since the appearance of Omicron, this average has increased to three days.

“We are dealing with an Omicron variant that has an incubation period, before the onset of symptoms, which has decreased from five to three days” specified in January Professor Yazdan Yazdanpanah, head of the infectious diseases division of the Bichat Hospital in Paris and member of the Scientific Council.

The Omicron BA.1 and BA.2 sub-variants confirm this trend: the incubation is faster, which has consequences for the rest of the process.

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Are we more contagious? Longer?

If the Omicron wave was so fast, it is because of the high infectiousness of this variant. “Omicron is about three times more transferable than Delta” estimated Health France in December, at the height of the wave. There are also differences between the sub-variants in terms of contagiousness. “BA.2 is 20% more contagious than BA.1”says Yannick Simonin, virologist and research professor at the University of Montpellier.

Another difference: the early contagiousness of carriers of the virus. “People infected with Omicron and its BA.1 and BA.2 subvariants become contagious much faster than with Delta”continues Yannick Simonin.

In Delta, the peak of infectiousness was reached an average of five days after infection. “With the BA.1 we went to 3.7 days, with the BA.2 in the majority today at 3.3”explains Yannick Simonin.

According to a Japanese study published in January 2022, viral load is elevated 3-6 days after Omicron is diagnosed or symptoms begin.

Different symptoms? Present longer?

A study published in April 2022 by the lancet confirms the observations of healthcare professionals in contact with patients. The researchers, who studied the testimonials of some 63,000 patients, all vaccinated for their infection, conclude: Infected people experience less loss of smell with Omicron than with Delta. In detail, only 17% of Omicron-infected patients lost their sense of smell, compared to 53% with Delta. Conversely, Omicron’s patient has more sore throat.

Still according to the study of the lancet, we are less symptomatic when affected by Omicron than we are with Delta: 8.3 days vs. 9.6 days. The difference is even greater with a previous booster vaccination: 4.4 days of symptoms with Omicron versus 7.7 days with Delta.

What about reinfection?

In France, 416,995 possible cases of reinfection were identified between March 2, 2021 and January 27, 2022, according to Public Health France. But 384,375, or 92%, have been since 1er December 2021. And above all, almost 80% of the possible cases of reinfection showed an infection related to the Omicron variant during the 2nd episode, a note from Public Health France reported in mid-February. In March, 5% of positive Covid cases in France were reinfections.

“The reinfection capacity of BA.1 and BA.2 is greater, confirms Yannick Simonin.Both sublines have the ability to evade the larger immune response. Particularly the BA.2, which explains why it quickly became the majority. It is therefore no longer rare for people to be infected again four to five months after a first Covid. †

Recent studies have even revealed cases of reinfection with BA.2 after an infection with BA.1, within a period of less than 60 days.

COVID-19. Incubation, infectivity, symptoms: what have the Omicron variants changed?

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