Influenza virus has high morbidity rates during annual epidemics, with certain high-risk groups being particularly susceptible to complications and mortality. Vaccination is the main prevention measure, alongside with hygiene measures. Nevertheless, vaccine coverage remains low.

Some studies suggest that short, standardized interventions can improve coverage of several vaccines.

Hypothesis: Brief Intervention is an effective tool in improving vaccination coverage in people who have initially rejected it.

Objective: To determine the effectiveness of a Brief Intervention in increasing influenza vaccination (IIV) coverage compared with the usual advice in people who refuse it.

Method: cluster randomized clinical trial. The study population was individuals with high risk factors who initially refused the influenza vaccine. Professionals participants (doctors and nurses) were assigned randomly to the intervention group (brief intervention) and the control group (usual advice).

General objective: To determine the effectiveness of the use of BI for IIV compared to the usual advice, in people who refuse to be vaccinated.

Specific objectives:

1. To examine the effectiveness of Brief Intervention compared to the usual advice in different risk groups (> 60 healthy, > 60 years old with a Risk Factor [RF], <60 years old with RF).
2. Quantify influenza vaccine coverage in people with the most frequent RF.
3. Record the patients' reasons for refusing to be vaccinated.

METHOD A cluster randomized controlled clinical trial. The reference population consisted of patients assigned to and treated by urban and rural health centres in the centre of Catalonia, an area with a population of approximately 405,000. 135,648 were the risk factor population that could be vaccinated against influenza virus.

The study population consisted of individuals with high risk factors who were treated in healthcare centres during the 2017 influenza campaign.

The study protocol was approved by the Research Ethics Committee (CEI) of the Institut Universitari d'Investigació en Atenció Primària (IDIAP Jordi Gol).

The participants (doctors and nurses) decided voluntarily whether or not to participate and they were randomly assigned to either the Intervention Group (IG) or the Control Group (CG).

The recruitment of patients suitable to participate in the study was carried out during the IIV campaign, as part of the health centre's routine activities. Patients with inclusion criteria who came to see a doctor or nurse were invited to participate in the study. Those who accepted participating signed an informed consent.

The intervention consisted of a standardized Brief Intervention for the Influenza Vaccination.

Data was collected anonymously and confidentially via the electronic health record of Catalonia [eCAP in Catalan]. The variables analysed for the two groups were: IIV at the end of the 2017 vaccination campaign (yes/no), age, IIV risk factors and reasons for non-vaccination.

Inclusion Criteria:

• Individuals in high-risk groups for influenza (paediatric and adult)
• Not intending to be vaccinated against the influenza virus during the current season.
• Informed consent to participate. In case of paediatric patients, parents signed the consent and made decisions about vaccination.

Exclusion Criteria:

• Language barrier
• Mental or physical conditions which make it difficult for the patient or their relatives to make decisions.
• Having previously participated in the pilot study.