• Wastewater treatment plants have shown an increase in the concentration of the virus in wastewater in Ile-de-France since mid-June.

  • This concentration of the virus in wastewater has never disappeared for a year as it had been the case after the first containment.

  • Vaccination and the preponderance of the Delta variant complicate data analysis.

We were expecting it at the start of the school year, the 4th wave of the Covid-19 epidemic arrived at the beginning of the summer. In Ile-de-France, the incidence rate exceeds 170 cases per 100,000 inhabitants, in Paris it is even close to 250. Against barely 35 at the beginning of the month. It remains to be seen how high this wave will be and especially its consequences on the hospital system. If the epidemic has shown on numerous occasions that it is difficult to predict, certain indicators nevertheless allow us to grasp early signs. Starting with the analysis of wastewater which can detect traces of viruses present in the body and evacuated by stool or urine. And for now, these first results leave little room for optimism, according to Vincent Maréchal, professor of virology at the University of the Sorbonne.

Are you seeing this epidemic recovery in wastewater?

Very clearly.

We first noticed this recovery around June 20 in Ile-de-France and in the Paca and Occitanie regions but since the beginning of July this rise has been visible almost everywhere on the territory.

In the Paris region, we are now at levels comparable to what they were last year, in mid-September, but the rate of increase is much faster.

Last summer, things had picked up slowly, whereas there, the slope is very steep.

This is confirmed when we look at the incidence rate, which is growing very rapidly under the effect of the Delta variant, which is more contagious than the British variant, which was itself more contagious than the original strain.

How far do you think this wave will go?

It's impossible to say but the latest readings, which date from mid-July, confirm that the dynamic is very fast.

This is all the more worrying since we never fell back to the level of last summer.

After the first confinement, which had been very strict, hardly any virus was detected in the wastewater between the end of May and the end of June before rising again throughout the summer.

What we see is that as soon as we release the braking measures, the epidemic resumes and the summer, contrary to what we heard at one point, does not block the circulation of the virus.

In general, the school holidays lead to a mixing of the population favorable to the spread of the epidemic.

Today, 50% of the population is fully vaccinated and 10% awaiting their second dose.

So it has no effect?

Obviously, and we can see it in Great Britain: the hospitalization curve is much lower than in previous waves.

But the vaccination rate is not yet sufficient to prevent the virus from circulating, more so from the Delta variant.

And we must keep in mind that even vaccinated, we can be infected.

On the other hand, the risks of developing a severe form are low.

Researchers from the Obépine network compare the concentration of viruses in wastewater, without knowing whether the person is symptomatic or not.

Does this mean that you could find significant concentrations of the virus without it materializing in a hospital wave?

This effectively complicates the analysis grid. We now know that vaccinated people who are infected have a lower viral load in nasal and salivary secretions, which is why they are ten to twelve times less likely to transmit the virus. But does this end up in the stool, which contributes most of the viruses found in wastewater? We don't know, there is a lack of studies on the subject. It's the same with the Delta variant: infected people have a very high viral load, but does this affect the stool? These are fundamental data because today, even if we are on a rate similar to that of last September, we cannot really compare the two situations.It is not known if a similar rate corresponds to the same number of infected people since a vaccinated person could reject less virus and a Delta attack, much more.

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  • Delta variant

  • Water

  • Coronavirus

  • Covid 19

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  • Paris

  • Urine