2.1.2 Rational for the lots  Lot 1. ECDC Hospital network for Vaccine Effectiveness, Burden and Impact Studies and Surveillance of  Severe Acute Respiratory Infections  The main public health problem posed by the COVID-19 pandemic consists in the large number of severe  cases that can overwhelm healthcare capacity and cause several deaths and disruptions for healthcare and  the society as a whole. A continuous assessment of vaccine effectiveness against severe COVID-19 (e.g.  severe acute respiratory infections caused by SARS-CoV-2), also in the presence of current and future  variants of concern, is therefore of key importance to confirm the positive impact of the intervention in  the population. Active, prospective, continuous, population-based surveillance systems for hospitalised SARI cases,  combined with laboratory testing, would reliably monitor incidence trends by place, time, aetiology, and  person thus allowing describing the seasonality of diseases including informing on the beginning and the  end of virus circulation, establishing baseline/threshold levels of activity for various viruses in order to  evaluate the impact and severity of each season, identifying and monitoring groups at risk of severe  diseases, estimating the impact of both pharmaceutical and non-pharmaceutical interventions on different  respiratory virus (e.g. COVID-19, influenza, etc). Furthermore, timely data from SARI surveillance can  inform patients’ recruitment strategies of ongoing clinical trials for vaccines and therapeutics and later on  for vaccine effectiveness monitoring. Finally, such system allows to generate data that can be used to  estimate disease burden and help decision-makers prioritize resources and plan public health  interventions. Over in the last quarter of 2020, ECDC started a project aimed at progressing enhancing  surveillance of SARI in EU and potential candidates in Western Balkan region 6 , with a long-term plan to  make such system stable and as inclusive as possible over time. Lot 2. Assessment of COVID-19 vaccine effectiveness among healthcare workers Healthcare workers are one of the most affected categories and are still suffering a high burden from  COVID- 19 pandemic. In the first phases of the pandemic until May 2020, an estimated total of 152 888  infections and 1 413 deaths due to COVID-19 were reported in healthcare workers globally 7 . Healthcare  workers can be subject to frequent repeated exposures to SARS-CoV-2 because of their profession. They  can also be exposed to high viral loads when managing patients and performing invasive procedures. This  enhanced viral exposure might have an impact on the effectiveness of vaccination in this group. Finally,  healthcare workers are professionally in close contact with patients at risk of severe COVID-19 and subjects  that may not be able to be vaccinated. It is therefore important to assess whether the vaccination can  prevent disease transmission from healthcare workers to patients as this indirect benefit cannot be  assessed in vaccine trials.  Lot 3. COVID-19 vaccine-related studies in long-term care facilities Long-term care facilities (LTCF) have been heavily affected by the SARS-CoV-2 pandemic 8 . Residents of  long-term care facilities are often vulnerable older adults at significantly increased risk of severe COVID- 19 and death due to COVID-19. This is due to the closed setting with a population with inherent medical  and social vulnerability. In many EU/EEA countries, residents of long-term care facilities have been the  6 Western Balkans, i.e. Albania, Bosnia and Herzegovina, Montenegro, Serbia, North Macedonia, and Kosovo (this designation is without prejudice  to positions on status, and is in line with UNSCR 1244/1999 and the ICJ Opinion on the Kosovo declaration of independence). 7  https://gh.bmj.com/content/5/12/e003097 8  https://www.ecdc.europa.eu/sites/default/files/documents/Increase-fatal-cases-of-COVID-19-among-long-term-care-facility-residents.pdf;  https://www.ecdc.europa.eu/en/all-topics-z/coronavirus/threats-and-outbreaks/covid-19/prevention-and-control/LTCF-data  11 