effectiveness, coverage, safety and impact monitoring activities specifically for COVID-19 vaccines. This includes the development of a structured post marketing monitoring platform for vaccines, including COVID-19 vaccines”. Indeed, efficacy measured in vaccine trials under experimental conditions may differ from effectiveness measured in real-life in a more diverse population under different conditions. Studies on the effectiveness and impact of COVID-19 vaccines and vaccination programmes will be critical to understand how the new vaccines will affect morbidity and mortality against several different outcomes, and thus determine their value and scope as a public health intervention in the context of the pandemic but also beyond. Additionally, the emergence of new more transmittable variants of concern that could partially escape the immunity induced by the vaccination, may cause the vaccine to decrease its effectiveness over time. 

## Influenza 

Annual seasonal influenza vaccination of risk groups including older individuals and individuals with specified medical conditions, and in some countries young children (6-36 months) or in others all children and adolescents (6 months- <18 years of age), as well as healthcare workers is considered the most effective single preventive measure against seasonal influenza. Monitoring the impact of seasonal influenza vaccination using different seasonal vaccine products and different vaccination strategies in the large European public health programmes is essential to assess risk and evaluate effectiveness. Influenza is a vaccine-preventable virus that undergoes frequent genetic and antigenic changes and therefore must be updated on a yearly basis. As a result, vaccine effectiveness (VE) has been shown to differ from year to year. 

The EMA Interim guidance on enhanced safety surveillance for seasonal influenza vaccines in the EU 3  and the EMA Guideline on Influenza Vaccines – non-clinical and clinical module 4  establish the requirement for manufacturers of authorised influenza vaccine to collect annual vaccine effectiveness results for their products. The latter requires product-specific seasonal influenza vaccine effectiveness studies to be conducted yearly by the vaccine manufacturers and is a result of the absence of well-defined immunologic correlates of protection. 

In the event of an influenza pandemic it is expected that an effective vaccine, when it becomes available, will dramatically reduce the burden of infections caused by the new pandemic virus. Therefore, efforts have been made world-wide to increase seasonal influenza vaccine production capacity also having an impact on the preparedness/capacity to produce pandemic vaccines. 

VE of influenza can be measured against different clinical outcomes such as Influenza-Like Illness (ILI), Acute Respiratory Illness (ARI), or Severe Acute Respiratory Infections (SARI) and laboratory-confirmed influenza infection utilizing GP networks, hospital networks or health-outcome database networks and different study methodologies (case-control, cohort, cluster, screening etc) are being utilized. 

Since 2007, ECDC has commissioned annual vaccine effectiveness studies among outpatients presenting to primary care in EU/EEA. The study results are available on ECDCs website 5  and protocols are available on request from ECDC. 

