Renaud Piarroux Head of department at the Pitié-Salpêtrière hospital (Paris)
Author of the wave. The epidemic seen from the field (CNRS éditions), Renaud Piarroux details for Humanity the specificities of the English and South African mutations of the virus and the possible consequences of their development on the epidemic.
Should we expect to see the epidemic regain strength in the days to come?
Renaud Piarroux Yes, but we will only be able to quantify this recovery in the course of next week. There have been two rounds of holidays, Christmas and then New Years Day, which have disorganized the surveillance of the epidemic a bit. The population was tested differently during this period. Just before the holidays, a lot of samples were taken, then less during, which complicated the observation of the circulation of the virus. But from the first half of December, the epidemic was already regaining ground. The number of cases had fallen in November, without going very low, to 10,000 per day. However, colleges and high schools were open, as were businesses. This is a first risk factor. We also know that winter temperatures favor the survival of the virus: people living in closed places, the virus evolves in better conditions.
What are you worried about about the current trend?
Renaud Piarroux Several points. In France, we are on a gradual rise. But we must take into account the English variant, which is very transmissible. For now, it has no impact on the dynamics of the epidemic. But we think this variant will develop within a few weeks. It’s mechanical. The strain that reproduces the most ends up gaining the upper hand. Among European countries, the country most affected by the English variant is Denmark. It’s a safe bet that, in a few weeks, it will also become preponderant.
What exactly do we know about this English variant?
Renaud Piarroux We know with almost certainty that the British variant is more transmissible (between 50 and 75%), and this in all age categories. Let me explain: when you are in contact with someone infected with the virus, you do not always catch it, fortunately. Great Britain has measured that contact with a contagious person carrying the variant has a 15% risk of catching it. While contacts of a person infected with the “classic” strain have a 9% chance of catching it. In an epidemic, hundreds of thousands of transmissions occur every week. After a while, the variant becomes dominant and this accelerates the epidemic. The effects on mortality and hospitalizations, on the other hand, do not appear to be increasing. That said, even if people infected with the variant do not have an increased risk of dying from it, since there are more sick, there are bound to be more deaths.
Another variant has been discovered in South Africa, is that also a concern?
Renaud Piarroux The South African variant is even more worrying, because it mutated in a more important way than the English variant, remained relatively close to the “classic” virus. South Africa is experiencing the same phenomenon as in England: another strain has become dominant, but in this specific case, it occurs in summer, a season normally less favorable for the virus. In addition, they face larger spikes in cases and mortality.
How can we recognize and detect this variant?
Renaud Piarroux Testing is not as simple as that of the “classic” virus. When we do a PCR search, we simply look to see if the virus’s RNA is present. To know if we are in the presence of the variant, it is more complicated: it is necessary to carry out a sequencing. We are looking for the piece of the virus genome that corresponds to the Spike protein and is used to attach the virus to our cells. This was done in the Parisian hospitals of Bichat and Pitié-Salpêtrière, where several hundred strains were sequenced. In addition, the British found that one of the PCR tests they used turned negative when applied to the variant. By doing several tests, they concluded that if the first is positive and the second negative, it is the variant.
What are the consequences of this data?
Renaud Piarroux This seriously complicates matters. Already there is no chance of finding it using an antigen test. If we do a PCR search, either the laboratory uses the PCR test faulted by the variant and the result will be false negative, or it uses another PCR test, which will detect that the patient has the Covid but without being able to say whether it is the variant or the “classic” strain.
Olivier Véran announced that around fifteen cases were infected with the English variant. But we can easily assume that there are more …
Renaud Piarroux It’s a certainty. In Paris, out of the two hospitals that receive the most cases, Pitié-Salpêtrière and Bichat, only one case was found out of several hundred sequences carried out. But we don’t know what’s going on elsewhere. There are also very suspicious cases identified via the Covisan system (screening and support system for positive people – Editor’s note). So we need to think about our surveillance system. Perhaps we should no longer do the same type of tests at all, it would take several PCRs to screen, check with sequencing … The English did it, the Danes do it too and, bad surprise, they started to see the variant appear.
Variant or not, what can be done to avoid an epidemic resumption?
Renaud Piarroux The tightening of measures seems unavoidable. The effect of the holidays will be felt in a few days. At best, we will stay on the same gentle slope as before the holidays, but it could be worse. Winter will last for a while, and the variant will develop. In February or March, it is very likely that it favors the dynamics of the epidemic. And we will not yet have vaccinated a sufficient part of the population.
Would there not already be things to improve in the “test-trace-isolate”?
Renaud Piarroux As applied at the moment, this strategy is ineffective in breaking the chains of transmission. There are effective devices, like Covisan, where the patient benefits from explanations, aids and collaborates more readily for the tracing of contacts. But it would take hundreds. I am campaigning for these measures to be extended, which are based on support and not on coercion. Nothing is done without the patient and his cooperation. Another problem, currently, you can get tested in many different places. Suddenly, the tests are not always good, and patient support is almost nil. In addition, if you get tested the day after contact, you will necessarily be negative, since it takes four or five days. If you don’t know, you’re going to think you’ve escaped the contamination. This is one of the side effects of a strategy where everyone is screened, at the risk of losing the quality of screening and support.