This is the first study performed within the ESPERES cohort, related to prevention against COVID-19, in particular vaccination against COVID-19 and more broadly on the COVID-19 pandemic.

ESPERES is a national prospective e-cohort study providing a resource for collecting information on healthcare workers (HCWs) currently working in France. The overall goal of ESPERES is to develop the infrastructure necessary to create and engage a community of HCWs who may be eligible for participation in future research studies. ESPERES is set up to answer research questions, in the field of prevention for HCWs, prevention for their own health, that of their relatives, their colleagues, and users of the hospital. These research questions will be carried out in the context of specific subsequent studies.

Most countries face the issue of vaccine hesitancy, with sizeable fractions, or sometimes the majority, of the public opposing some vaccines. The problem is particularly acute in the case of COVID-19 vaccination: first, a high uptake of COVID-19 vaccines is necessary to reach and sustain herd immunity; second, and to the best of our knowledge, no country is currently planning on making COVID-19 vaccination mandatory, making public approval essential. Unfortunately, hesitancy towards COVID-19 vaccines is high in many countries.

Vaccine hesitancy also concerns healthcare workers (HCWs) who are at the frontline of the COVID-19 pandemic and identified as a priority target group for COVID-19 vaccines. Furthermore, HCWs can be relays of information concerning vaccination and thus play a key role as mediator in the promotion (or not) of this vaccination. However, vaccine intentions against COVID-19 are not fully known among different categories of HCWs and are likely to evolve with knowledge about the safety and efficacy of vaccines as well as the evolution of the epidemic. Consequently, it is crucial to understand the evolution of these vaccine intentions and their determinants in HCWs in order to better target interventions to promote this vaccination, in a context where scientific data are themselves evolving quickly.

The study population will be made up of HCWs. For the purposes of this study, a "healthcare worker" is defined as an individual who currently works in a setting where individuals receive healthcare (i.e. individuals do not have to work directly with patients, but may have any role within a setting where individuals receive healthcare, such as administrative office, housekeeping, food service, etc.). ESPERES_COVID-19 will be offered to all the HCWs of the Assistance Publique - Hôpitaux de Paris (AP-HP) establishments and to other public or private health establishments (lucrative or not) in the Ile-De-France region and to establishments in other French regions, in order to diversify the contexts.

Each participant is self-included and collects his own data via a web interface. This cohort is open, meaning that eligible people can be included until the end of the study (no limited inclusion period). This cohort will start in 2021 and is scheduled for an initial duration of 24 months but may be extended as part of amendments.

Participants will be regularly asked to answer online questionnaires lasting at most 20 minutes. The frequency of these questionnaires will not exceed one questionnaire every 2 weeks (and will generally be more spaced out). During their follow-up in the cohort, participants may be asked, depending on their characteristics, to participate in studies nested in the cohort.

All data from ESPERES_COVID-19 will be gathered in a health data repository. The statistical analyses planned in the research protocol will be performed by the pharmaco-epidemiology center (CEPHEPI), under the responsibility of Dr Candice ESTELLAT and Pr Florence TUBACH. The CEPHEPI is backed by the public health department of the hospital group Pitié-Salpêtrière - Charles Foix, AP-HP.

A calculation of the sample size is not justified for this study as it aims to answer several research questions in a cohort. However, a number about 15,000 participants in ESPERES_COVID-19 are expected.

Inclusion Criteria:

• Legal age
• Healthcare workers defined as individuals who currently work in a setting where individuals receive healthcare (i.e. individuals do not have to work directly with patients, but may have any role within a setting where individuals receive healthcare, such as administrative office, housekeeping, food service, etc.)
• Agreeing to participate (digital consent)

Exclusion Criteria:

- No internet access

The study population will be made up of HCWs. For the purposes of this study, a "healthcare worker" is defined as an individual who currently works in a setting where individuals receive healthcare (i.e. individuals do not have to work directly with patients, but may have any role within a setting where individuals receive healthcare, such as administrative office, housekeeping, food service, etc.). ESPERES_COVID-19 will be offered to all the HCWs of the Assistance Publique - Hôpitaux de Paris (AP-HP) establishments and to other public or private health establishments (lucrative or not) in the Ile-De-France region and to establishments in other French regions, in order to diversify the contexts.