# Covid-19: the R0 remains below 1 in France

The R0, indicator of the circulation of Covid-19 remains below 1 except in New Aquitaine, informs Santé Publique France in its last weekly epidemic bulletin. What is the R? How is it calculated? Explanations.

Since the start of the coronavirus epidemic, there has been a lot of talk about R effective, an indicator presented as the reflection of the speed of spread of Sars-Cov-2, the virus responsible for the Covid-19 disease. But what is it exactly?

In medical language, we say that the effective R0 or R is the basic reproduction rate of a virus. Clear : “this is the number of people who can potentially be infected by an individual infected with a virus“explains Dr. William Berrebi, gastroenterologist and hepatologist, and former intern at the Hospitals of Paris.

The R0 indicator is therefore not specific to the Sars-Cov-2 coronavirus: it can be measured for any viral epidemic. “At the height of the coronavirus epidemic, at the end of March 2020, the R0 was 3 which means that each infected person could transmit the virus to around 3 other people, says Dr. Berrebi. For comparison, the R0 of the measles is 16 and that of the gastroenteritis is 17: these are viruses that circulate much more easily than Sars-Cov-2 in the population.

## The effective R (R0) remains below 1 in France

Some benchmarks. When the R0 of an epidemic falls to 0, the virus no longer circulates and the epidemic is extinguished: on the contrary, the higher it is, the more the epidemic grows. “When the R0 exceeds 1, it is estimated that the epidemic is active: at the time, this corresponded to the departments in orange on the map of France, notes Dr. Berrebi. When it reaches 1.5, it is an alert threshold. “

On June 11, 2020, the R0 of Sars-Cov-2 fell to 0.73 “especially thanks to the measures of confinement“recalls Dr. Berrebi. As of June 6, 2021, it is 0.83.

In his June 3 epidemiological bulletin, Public Health France observes a “continued improvement of epidemiological indicators and reduction of hospital pressure.” The health authorities stress, however, that “in the context of the lifting of health restriction measures, the circulation of worrying variants should encourage the maintenance of all control measures”.

As for the effective R, it is falling and below 1, a sign that the epidemic is declining. To calculate it, Public Health France relies on three types of data: virological data (tests), hospitalizations and emergency room visits.

As of June 3, “the estimate of the effective reproduction number was significantly greater than 1 based on virological data in Nouvelle-Aquitaine, but remained below 1 from the other two sources, specifies SPF. In other metropolitan areas, estimates of effective breeding number were all less than 1 from all three data sources. “

Likewise, in the meeting, the estimate of reproduction number was insignificantly greater than 1 from all three data sources.

 R effective (PCR) R effective (emergencies) Effective R (hospitalizations) Auvergne-Rhône-Alpes 0,86 0,84 0,73 Bourgogne-Franche-Comté 0,85 0,89 0,85 Brittany 0,87 0,79 0,84 Loire Valley Center 0,86 0,77 0,69 Corsica 0,72 – – Great East 0,86 0,80 0,71 Hauts-de-France 0,79 0,70 0,67 Ile-de-France 0,78 0,75 0,69 Normandie 0,80 0,83 0,79 New Aquitaine 1,03 0,92 0,85 Occitanie 0,92 0,84 0,79 Pays de la Loire 0,86 0,91 0,79 Provence-Alpes-Côte d’Azur 0,82 0,81 0,85 Guadeloupe 0,76 0,87 0,74 Guyana 0,90 0,99 0,90 The meeting 1,03 1,13 1,18 Martinique 0,87 – – Mayotte 0,48 – –

## Coronavirus: how to lower the R0?

The rise in R0 corresponds to a relaxation of barrier gestures in the population. It is very important to wear a protective mask when traveling and to respect all barrier gestures (hand washing, distance, ventilation, etc.) to limit the spread of the virus responsible for Covid-19.

Another effective strategy:test and isolate each patient affected by Covid-19: “if the infected persons are identified early enough with the help of tests, we can (in a way) take these people out of the circuit and prevent them from contaminating those around them, thus avoiding the spread of R0“- this is the strategy recommended by the World Health Organization (WHO).

But for the specialist, it is likely that only vaccination will really put an end to the coronavirus epidemic: “it is thanks to the vaccination that the R0 of the seasonal flu fell to 0.5: it is therefore very likely that while awaiting the vaccination of the entire population against Covid-19, there will be permanent oscillations at the level of this key indicator“.

Thanks to Dr. William Berrebi, gastroenterologist and hepatologist, former intern at the Hospitals of Paris, author of the podcast Thank you Doctor ! and of Viruses-animals-humans: (very) dangerous links – From AIDS to Covid-19.