Interim public health considerations for the provision of additional COVID-19 vaccine doses


European Centre for Disease Prevention and Control. Interim public health considerations for the provision of
additional COVID-19 vaccine doses, 1 September 2021. ECDC: Stockholm; 2021.

This document aims to provide the target audience with interim public health considerations for the provision of additional COVID-19 vaccine doses. The most recent evidence regarding vaccine effectiveness against symptomatic and asymptomatic infection due to the circulating variants and regarding duration of immunity will be briefly summarised. Considerations around the implementation of additional COVID-19 vaccine doses will also be discussed. This document does not aim to provide recommendations about the administration of additional doses of COVID-19 vaccines but summarises the current evidence and outlines options for consideration by public health authorities.

Executive summary

Key messages

  • Providing all eligible individuals with the recommended dose regimen should remain the current priority for COVID-19 vaccination programmes in the European Union/European Economic Area (EU/EEA).
  • It is important to distinguish between ‘booster’ doses for people who responded adequately to primary vaccination and additional doses for those with weakened immune systems who did not respond adequately. Booster doses are given to vaccinated people (i.e. those who have completed a primary series of COVID-19 vaccination) to restore protection after it would have waned. On the other hand, additional doses as part of a primary vaccination series may be given to people with severely weakened immune systems, as they may not achieve an adequate level of protection from the standard primary vaccination.
  • When assessing the need for possible booster doses of COVID-19 vaccine from the public health perspective, it is important to keep in mind the main objective of the vaccination strategy (i.e. preventing severe cases of COVID-19). Vaccine effectiveness against severe disease should preferably be chosen as the primary outcome of interest for assessing whether there is a clear need for a booster dose in specific groups.
  • The available evidence at this time regarding ‘real world’ vaccine effectiveness and the duration of protection shows that all vaccines authorised in the EU/EEA are currently highly protective against COVID-19-related hospitalisation, severe disease and death, suggesting there is no urgent need for the administration of booster doses of vaccines to fully vaccinated individuals in the general population.
  • The option of administering an additional vaccine dose to people who may experience a limited response to the primary series of COVID-19 vaccination, such as some categories of immunocompromised individuals (e.g. solid organ transplant recipients), should already be considered now. This is to be seen as an extension of the primary vaccination series for these specific groups, and not as a booster. Consideration could also be given to providing an additional dose as a precautionary measure to older frail individuals, in particular those living in closed settings (e.g. residents of long-term care facilities).
  • Full vaccination against COVID-19 of all eligible family contacts and close contacts, including professionals providing care, of immunocompromised and vulnerable individuals should also be considered.
  • Close monitoring of vaccine effectiveness data and breakthrough infections, particularly among vulnerable groups at risk of severe COVID-19 and among those living in closed settings, should be continued, and decisions adapted accordingly, should a substantial decrease in effectiveness be noted in one or more population groups.
  • When in contact with individuals at risk of severe disease, physical distancing (when applicable), the wearing of face masks (especially when physical distancing cannot be kept), and hand and respiratory hygiene remain pivotal measures for reducing the risk of SARS-CoV-2 transmission. These non-pharmaceutical interventions should always complement vaccination, in particular in high-risk settings such as long-term care facilities or hospital wards with patients at risk of severe COVID-19.
  • More solid data are needed to inform future policies on booster doses. Knowledge gaps are particularly related to the appropriate correlate of protection to consider for the different population groups and the time from primary vaccination series until a booster dose should be given, and duration of immunity according to e.g. different age and risk groups, vaccine product, dosing interval, variant of concern (VOC), and homologous/heterologous schedule. Prospective vaccine effectiveness studies, as well as surveillance of breakthrough infections in the general population and in specific groups, are needed to answer these questions.
  • The benefits and risks of possible booster doses need to be clearly outlined and compared. Benefits may include increased protection against severe disease, mild-to-moderate disease, post COVID-19 condition (often called ‘long COVID’), SARS-CoV-2 infection, and virus transmission. Risks include possible safety concerns and public health implications (e.g. impact on vaccine confidence and uptake, global availability of vaccines).
  • Communication about possible additional vaccine doses should be carefully considered and delivered in a transparent, proactive, and clear way to avoid affecting vaccine confidence. The distinction between strengthening the response to primary vaccination series, for example in immunocompromised individuals, and boosters for waning immune response or vaccine escape, should be clearly made.
  • In the context of many countries outside of the EU/EEA still struggling to receive and administer enough vaccine doses to their populations, special consideration should be given to the current global shortage of COVID-19 vaccines, which could be further worsened by the administration of booster COVID-19 vaccine doses for the general population in EU/EEA countries.