The emergence and spread of new variants in France are being closely monitored by health authorities as part of the EMER-GEN consortium, coordinated by Santé publique France and the ANRS / Emerging Infectious Diseases (MIE), in collaboration with the National Reference Center for Respiratory Infection Viruses (Institut Pasteur and Hospices Civils de Lyon), two additional high-throughput sequencing platforms (APHP Henri Mondor and IHU Marseille), and a network of local laboratories coordinated by ANR / MIE. The goal of this system is to detect the emergence of variants of concern (VOCs) within the country as early as possible, given their characteristics (greater transmissibility, increased pathogenicity, and/or immune evasion), and to contain or delay their spread. The B.1.351 variant is one of four currently classified as variants of concern (VOC).

The identification of cases of the B.1.351 variant, imported from Mozambique, occurred at a time when the characteristics of this variant were still poorly understood. To our knowledge, these were the first cases identified in France, and indeed in Europe, and the first indication of the circulation of this variant in Mozambique. The information available at the time of the alert, indicating that several people who had traveled together were residing in different regions of France, highlighted a real risk of spread across the country. It was therefore essential to implement a rapid and targeted response by applying the necessary control and management measures to limit this spread. At the same time, it was necessary to document the characteristics of the identified cases and the associated modes of transmission in order to advance the state of knowledge regarding this emerging variant and potentially adapt case management measures.

Identifying, isolating, and testing close contacts of SARS-CoV-2 cases is the primary tool at our disposal for limiting the spread of the virus and its variants. In the context of the emergence of a new variant, such as B.1.351, this strategy had to be implemented as quickly as possible and with a focus on comprehensiveness. The primary objective of the investigations conducted was thus to identify all individuals encountered by cases during their infectious period, within their personal or professional spheres (including school settings), and to determine the level of risk posed by these contacts (contact tracing). These investigations were essential to document the epidemiological characteristics of these variants, enable the implementation of management measures tailored to the risk level of each situation, and limit the spread of this variant.

Numerous stakeholders were thus mobilized to conduct investigations, trace transmission chains, and implement appropriate control and management measures at both the individual and community levels. The contact-tracing teams of the Primary Health Insurance Funds (CPAM) conducted the initial investigations, focusing primarily on the personal sphere of the cases. The Regional Health Agencies (ARS), supported by the regional units of Santé publique France, conducted additional investigations, primarily among communities identified as at risk, so that enhanced control and management measures could be implemented to address this variant, which was then poorly understood. These teams worked closely with the Operational Hygiene Teams (EOH), responsible for risk analysis and management within hospitals; the Ministry of National Education, an essential partner for risk management in schools; and occupational health services for the workplace. Regular coordination took place with the laboratories responsible for the biological diagnosis of cases and their contacts.

In addition to the standard management measures typically implemented for SARS-CoV-2 cases and their at-risk contacts, enhanced measures were applied. Mobile teams were deployed to offer at-home testing to some at-risk contacts and to conduct expanded testing campaigns in the affected schools and workplaces. Testing campaigns were also conducted in parallel at designated hospitals.

The cases and high-risk contacts we identified were located in different metropolitan areas. This required national coordination to manage the situation.

Contact tracing is conducted at the departmental level by the CPAMs and at the regional level by the ARSs. The regional units of Santé publique France, present within each ARS, provide support for investigating complex situations such as this one. Thanks to their proximity to frontline workers and their networked organization across the entire country, these teams were able to centralize the information collected in each region and thus trace the various chains of transmission at the national level. This specific organizational structure of Santé publique France facilitated coordination with frontline actors managing the SARS-CoV-2 epidemic, resulting in a comprehensive overview of the situation that enabled the formulation of risk management recommendations.

The involvement of stakeholders, each with their own specific expertise—and expertise in their respective fields—facilitated the management of this complex situation and helped limit the spread of the B.1.351 variant across the country from these imported cases. This multidisciplinary approach among public health stakeholders represents real added value for managing high-risk health situations in all their dimensions. The sharing of information, from the local to the national level, and the centralization of data necessary to describe a complex situation demonstrate the benefits of operating within networks.