This evidence review was compiled by members of the CITF Secretariat with the input from experts affiliated with the CITF and does not necessarily reflect the views of all CITF members.

By Varun C. Anipindi

While countries around the world are working to get their populations vaccinated, the emergence of SARS-CoV-2 variants of concern (VOCs) has threatened our return to normalcy. With the rise of breakthrough infections associated with the Delta variant, public health agencies in middle- and high-income countries are debating the need for booster shots to ensure enhanced protection against COVID-19. However, this raises an ethical dilemma given the prevailing lack of vaccine access in low-income countries. Editors from major journals such as Science and BMJ have published editorial articles discussing how to best navigate the ongoing pandemic in an equitable manner.

Key points:

  • The Delta variant has quickly become the predominant circulating strain of SARS-CoV-2 in many countries, including the USA, where it represents ~90% of current cases (1). Some of these infections are defined as breakthrough infections, i.e. they are occurring in fully-vaccinated individuals (1).
  • The increasing incidence of these breakthrough infections in fully vaccinated people is prompting the consideration for booster shots (or a third dose), especially for those at increased risk of infection (i.e., elderly, immunocompromised, healthcare workers and others) (1, 3). Scientists nevertheless agree that for most individuals, a complete round of vaccination (two doses for most vaccines) remains highly effective in protecting against hospitalization and severe disease (1).
  • While mid- and high-income countries debate the need for additional shots amongst vaccinated individuals, other countries remain in dire need for first and second doses of vaccines. Among the ~35 million vaccine doses administered daily around the world, only 1.3% of these are being provided to those living in lower-income nations (2, 3).
  • To combat the issue around vaccine access and inequity, the World Health Organization (WHO) has placed a moratorium against booster shots until at least 10% of every country is vaccinated. However, many countries (i.e., Israel, Turkey, USA, UK, Uruguay, Cambodia, Thailand, Germany) are pursuing third doses or booster shots for specific populations. This includes testing heterologous (mix/match) strategies in efforts to improve vaccine efficacy (3).
  • Fiona Godlee, the editor in chief of BMJ discussed considerations such as the relaxation of patent laws and globalization of SARS-CoV-2 vaccine manufacturing in an effort to improve vaccine access for all nations. Ultimately, she suggests this may be the only way to effectively move past the COVID-19 pandemic, given its global nature (2).


  1. Vogel G. Do Delta ‘breakthroughs’ really mean vaccine protection is waning, and are boosters the answer? August 20, 2021. doi:10.1126/science.abm0319
  2. Godlee F. Vaccines should not be the preserve of rich countries. BMJ 2021;374:n2044, doi:
  3. Mahase E. Covid-19 booster vaccines: What we know and who’s doing what. BMJ 2021;374:n2082, doi: