The use of nanomaterials in semi-facial respirators could decrease the permeability of particles and promote a biocidal effect compared to conventional respirators (N95) and, therefore, to enhance the filtering power, aiming to mitigate harmful effects of bacteria and viruses. Chitosan is a natural cationic polymer derived from chitin, with characteristics such as being biodegradable, biocompatible, non-toxic, and presenting antimicrobial activity. This polymer has virucidal activity in several types of viruses, including other coronaviruses, given the attractive factor of its cationic charge for negative charges. The effectiveness of a novel individual protection semi-facial respirator (called VESTA) will be investigated, compared to a conventional N95 respirator. The respirators will be tested in healthcare professionals working in hospital environments and the effectiveness will be attributed to the lower incidence rate of infection by the SARS-CoV-2, and to the ability to filter these viruses after use by healthcare professionals exposed to potentially contaminated environments. The study will be carried out in two stages: i) Randomized Controlled Trial with reduced sample to confirm the sample size calculation (pilot trial), and ii) Randomized Controlled Trial (RCT). The RCT will be conducted with healthcare professionals who have contact with environments/patients infected by SARS-CoV-2 in hospital sectors with greater vulnerability to infection (urgency, emergency and intensive care units). The RCT will be conducted initially with a group of sixty participants (n = 30 in each group) for initial investigation of the potential for efficacy with the use of the respirators (VESTA and conventional N95) in two sectors (emergency and ICU) in a reference Hospital for COVID-19. The RCT will consist of two parallel groups: (1) Experimental Group (GExp) that will use the novel respirator (VESTA) and (2) Control Group (CG) that will use the standard respirator (N95). Participants will be recruited from participating hospitals and will be accompanied by 21 days in approximately eight consecutive shifts (ranging from shifts lasting 6 to 12 hours each, followed by approximately 36 hours of rest). Participants will be assessed at baseline (T0), at the end of the 10th day (T1), and at the end of the 21st day (T2).

Context for the latest register update (May, 2022): Our randomized controlled pilot trial was conducted from February until April 2021, following the same methodological procedures described within the clinical trial register. After analyzing the data from the pilot trial we included some updates within the clinical trial register. Summary of changes after the pilot trial: 1) We performed a new sample size calculation, which resulted in a sample size of 700 participants (n=350 in each group). This information was updated within the trial register; 2) We removed the secondary outcome "Ability of the filtering element to inactivate the SARS-Cov-2". The team decided that this outcome would be more appropriately assessed in a controlled laboratory study, and not associated with the clinical trial. Thus, this outcome will be investigated in a secondary study; 3) We decided to include the clinical assessments (Job stress, Quality of life, Musculoskeletal discomfort, Burnout, and Work ability) exclusively as baseline measurements.

Inclusion Criteria:

• Full-time employees (defined as direct patient care for more than 24 hours weekly) and work primarily at the study site or co-participants (more than 75% of working hours).
• Professionals working in emergency departments, ICUs, and other hospital settings exposed to SARS-Cov-2.
• Negative clinical and laboratory results for SARS-Cov-2 infection (negative RT-PCR).
• Have previous experience using N95 PFF2 respirators.

Exclusion Criteria:

• Pregnant or breastfeeding women.
• History of high-risk comorbidities, such as high-risk heart disease or respiratory diseases.
• Presence of heterogeneous facial anatomical characteristics such as bulky beard, facial deformities, or facial dimensions incompatible with the respirators.

The outcome assessor won't have any knowledge about the study purposes and will be unaware of the group allocation.

Participants will be blinded as they will not distinguish the novel respirator (VESTA) from the conventional N95 respirator (both will have the same shape, color and size).

The statistical analysis will also be performed blinded for group allocation.