COVID-19 vaccine boosters

Written by: Rosie Lobley and Ben Caldwell

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The ongoing rollout of vaccination against COVID-19 in high-income countries around the world has gradually become overshadowed by the increasing prevalence of the Delta variant.1 COVID-19 vaccines become significantly less effective when faced with the Delta variant than against earlier variants of the virus.2

COVID-19 vaccine boosters

There is not yet enough evidence to indicate whether the drop in protection offered by vaccines against the Delta variant is solely down to the heightened virulence of the variant itself, or whether other external factors – such as an increase in close contact between vaccinated patients3 or waning efficacy of the vaccines over time4 – contribute to the issue. Irrespective of the cause or causes of the fall in protection against the Delta variant, a number of public health bodies are now advocating the administration of a third ‘booster’ dose of COVID-19 vaccines.5

How vaccine boosters work

Booster doses of vaccines cause the B cells responsible for producing antibodies to replicate and evolve, meaning that not only are more antibodies produced, but that those antibodies may be more powerful at fighting off disease.6 The world’s first study of the merits of COVID-19 vaccine boosters launched in the UK in May 2021, with the final results projected to be ‘some weeks away’ as of 8 September.7

In late August 2021 the World Health Organization’s (WHO) regional director for Europe, Dr Hans Kluge, endorsed the distribution of COVID-19 boosters as ‘a way to keep the most vulnerable safe’, citing ‘significant growth’ in infection rates driven by the Delta variant.8 This represented a shift in policy by the WHO: earlier in the month, WHO director-general Dr Tedros Adhanom Gebreyesus had called for a moratorium on boosters until the end of September at the earliest, to enable less wealthy countries to catch up by vaccinating at least 10% of their populations.9

Equity and availability

As higher-income nations begin to discuss and implement booster dose programmes, low- and middle-income countries (LMICs) are struggling to deliver first doses. Just over 6% of the population of Africa have received even a first dose of the vaccine, and only 4% are fully vaccinated.10 The COVID-19 Vaccines Global Access (COVAX) Facility, which aims to ensure worldwide equity in access to vaccines, reported vaccine shortages earlier in 2021 due to supply chain issues.11 Meanwhile, high-income countries are stockpiling more doses than they need – the US has thrown away at least 15.1 million doses since 1 March.12

COVID-19 vaccine hoardingThere are a number of factors affecting the unequal distribution of vaccines, aside from ‘vaccine nationalism’.14 Restrictions on international exports have hindered the supply of vaccines to LMICs, while strict intellectual property legislation means that LMICs are unable to manufacture doses themselves. High-income nations, which were hit harder than expected in the early stages of the pandemic, have not entirely delivered on promises to donate vaccines to lower-income regions, which are unable to fund the needed supply of doses in a competitive market.15

Just over 6% of the population of Africa have received even a first dose of the vaccine, and only 4% are fully vaccinated.

Aside from the humanitarian implications of implementing internal booster programmes before ensuring international distribution of first and second vaccines, vaccine ‘hoarding’ by wealthier nations16 carries the risk of wider impacts – most significantly, the threat of new, potentially more virulent or vaccine-resistant variants of COVID-19 evolving and proliferating in unvaccinated regions.17

COVID-19 vaccine equity


While more high-income countries are adopting vaccine booster programmes, the evidence in favour of these programmes remains limited at best.32 The stockpiling of vaccines by wealthy nations raises both practical concerns – projections suggest that richer countries will be in possession of a billion excess, unused doses by the end of 202133 – and ethical questions over the advisability of vaccine hoarding.34 Effectively, the epidemiological risks associated with allowing the virus to continue to spread in regions which cannot afford widespread vaccination mean that the sooner booster programmes are rolled out, the greater the likelihood that additional doses will be needed.35

The stockpiling of vaccines by wealthy nations raises both practical concerns and ethical questions over the advisability of vaccine hoarding.

However, with winter rapidly approaching, clinically vulnerable, immunosuppressed and elderly groups are increasingly at risk of infection even if they are fully vaccinated – as are health and care workers on the front lines.36 Health and care services are already expected to face significant challenges in winter 2021 due to the heightened spread of respiratory syncytial virus, colds and flu;37 and the delivery of third dose boosters to at-risk groups in the autumn may help to ease some of the pressure those services face.38

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