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What are characteristics of Covid variant JN1, now dominant in France?

Experts say its mutations mean it can infect lung cells more easily but that it is also less contagious

A view of a test tube with a positive check for JN.1

JN.1 has a ‘huge number’ of mutations, at 30, experts have warned, making it more resistant to the immune system Pic: vishal jyani / Shutterstock

Researchers in France have raised concerns over the Covid subvariant JN.1, which now accounts for 70% of the new infections in the country, mainly because of the effect it can have on patients’ lungs.

The subvariant - which itself comes from the Covid-19 variant Omicron and its subvariant Pirola (BA.2.86 - is spreading across the country, said health authority Santé publique France (SPF) in its latest update (January 10).

More precisely, SPF said its flash surveys had found that JN.1 now represents around 67-70% of the interpretable sequences, up from 62% the previous week.

JN.1 was first detected in France last summer, but experts are now saying that it is responsible for the uptick in cases seen in many European countries at the end of 2023 - the sharpest rise in cases in France since the end of 2021.

This month, the US Centers for Disease Control and Prevention (CDC) reported that the variant accounted for around 62% of Covid-19 cases worldwide: a significant increase on previous weeks.

Read our previous articles 

‘More resistant but less contagious’

Some scientists have even said that JN.1 could be one the most dangerous variants since the appearance of the Delta strain in 2020, due to the number of mutations (more than 30), which make it more resistant to the immune system. 

Dr Bruno Lina told La Dépêche: “That’s huge. The only time we saw this number was when we discovered Omicron. Prior to that, we had only seen 18 [mutations].”

Professor Vincent Enouf, deputy director of the Centre national de référence (CNR) for respiratory infection viruses at the Institut Pasteur, told Le Figaro that “because of these new mutations, it is possible that it will be recognised less by our immune system”.

JN.1 may be able to infect cells in the lower part of patients’ lungs more easily than previous variants, suggests recent research published in the medical journal Cell, from scientists at Ohio State University in the US. These cells are called ‘human lung epithelial cells’ and they help to protect the respiratory system.

This variant’s ability to infect these cells more easily makes it more likely to escape the body’s immune response, the researchers said, which means it could lead to more severe illness in vulnerable individuals.

Yet, SPF stated in its update: “We do not have precise data on its potential impact on public health…[but at this stage] there is nothing to indicate that JN.1 has different characteristics to the other sub-lineages of BA.2.86.”

It added that this variant seems “more resistant” to the body’s antibodies, but “less contagious” than previous strains.

A new winter wave?

In November 2023, Covid-19 expert Professor Antoine Flahault said that JN.1 could be one of the variants - along with Pirola - that could contribute to what he called a “new winter wave” of the virus.

He told La Dépêche: “When [JN.1] exceeds 50-60% of the sequences analysed, it should cause the epidemic curve to bend, leading to a rise in incidence, and then very probably to a new wave, this time in winter.”

So far, SPF said that it had “not identified any signals of concern for either BA.2.86 or JN.1”, but that “there are still cases under investigation which may affect these results”.

SPF said that currently, cases of the virus are not rising. Yet, it said that it is “still active”, and that the percentage of JN.1 cases identified is growing.

Symptoms of JN.1 

The symptoms of JN.1 are similar to those of previous variants, but it can also cause a runny nose (as well as fatigue, fever, headaches, a cough, and sore throat). Some people have also reported feeling short of breath and digestive issues. 

Some have reported a loss of taste and smell, but this symptom is less common now than for previous strains.

The new updates on Covid-19 came as part of SPF’s regular updates on the current winter epidemics.

Flu is currently at epidemic levels in 11 departments, and pre-epidemic in two; while bronchiolitis is still at epidemic levels in eight departments, but there has been a drop in hospital trips for infants under two years of age. 

Read more: Flu, bronchiolitis, Covid: How epidemics are progressing in France

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