Booster shots for COVID-19—the debate continues
Authors: Talha Burki
Journal: The Lancet Infectious Diseases (2021)

As a minority of countries consider offering booster doses of COVID-19 vaccines to their citizens, the majority are yet to vaccinate their entire populations with a single dose. Talha Burki reports. On Sept 1, 2021, the European Centre for Disease Prevention and Control (ECDC) issued a technical report outlining the public health case for booster doses of the COVID-19 vaccines. It concluded that fully vaccinated individuals in the general population are in no urgent need of a booster shot. The report recommended that member states instead prioritise the one-third of adults in the EU and European Economic Area who have not yet received both doses of the COVID-19 vaccine. “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”, added the ECDC. WHO Director-General Tedros Adhanom Ghebreyesus has voiced similar concerns. On Aug 4, he called for a moratorium on boosters. “We cannot accept countries that have already used most of the global supply of vaccines using even more of it, while the world's most vulnerable people remain unprotected”, said Tedros. At the time of his statement, people in high-income and upper-middle-income nations had received over 80% of the doses of COVID-19 vaccines administered around the world. WHO has warned that 42 states in Africa are likely to miss the target of vaccinating the most vulnerable 10% of their population by the end of September. Around 3% of Africans have been fully vaccinated, compared with 52% of Americans. Several countries decided to ignore Tedros’ suggestion. White House Spokesperson Jen Psaki described the idea that the USA would have to decide between booster shots for its own population and donating vaccines to poorer nations as a “false choice”. “We can do both”, she added. Joe Biden has set a goal of Sept 20 to start offering adults the option of a booster dose, although this will depend on recommendations from the US Food & Drug Administration and the Centers for Disease Control and Prevention (CDC). The CDC has already advised that individuals in immunocompromised groups receive an additional shot of the COVID-19 vaccine, although this would be more accurately defined as the final dose in the standard vaccine regimen, rather than as a booster. Since Aug 13, 1·33 million Americans have had a third shot of a COVID-19 vaccine. It is unclear how many of these people were not immunocompromised. Reports have emerged of some Americans arranging unofficial booster doses. The UK is also considering introducing a third shot of the COVID-19 vaccine for adults, and France and Germany plan to provide an additional dose to vulnerable groups such as residents of long-term care facilities and elderly people. The only nation to have already rolled-out booster shots is Israel. Daniel Weinberger is associate professor of epidemiology at the Yale School of Public Health (New Haven, CT, USA). In collaboration with KSM, the research and innovation centre of Maccabi Healthcare Services, Weinberger co-authored a study, which has not yet been peer-reviewed, exploring the early evidence from the Israeli campaign. It found that the chances of an individual testing positive for SARS-CoV-2 were sharply reduced in the days following their booster jab. “Your immunity against infection wanes over time; boosters restore your level of immunity to somewhere around where it was after the second dose”, explained Weinberger. “But we still do not know how much immunity wanes for severe infection; if it is not waning to the same extent, then it is not clear that a booster would be warranted for the general population.” The ECDC report stressed that the major purpose of the mass vaccination campaigns against COVID-19 is to reduce severe disease. But pinpointing the relationship between severe disease and the antibody response induced by the vaccine is not straightforward. “We do not know how long the protective antibodies last from the second dose of the COVID-19 vaccine”, said Martin Hibberd, professor of emerging infectious diseases at London School of Hygiene & Tropical Medicine (London, UK). “We know that the total amount of antibodies drops relatively quickly after the second dose, and often there is a relationship between that and your overall level of protection, but the specific neutralising antibodies that inhibit the virus, and account for the protective effect of the vaccine, are very difficult to measure.” Matters are further complicated by the shifting nature of SARS-CoV-2. The vaccines currently in use are based on the original virus. They remain highly effective in preventing hospitalisation and death from the far more transmissible delta variant (also known as B.1.617.2) but are less effective in preventing infection. It is virtually impossible to unpick the extent to which infections among fully vaccinated individuals are down to waning immunity from the vaccine, the surge in the delta variant, or reduced adherence to physical-distancing measures. Hibberd advocates booster shots that target the delta variant. “The only way to confirm the duration of the protective antibodies would be to wait until more and more vaccinated people are getting sick”, he said. “If we start giving boosters to people before their immunity has faded, we can get ahead of the virus, for once.” He pointed out that the mRNA vaccines that will be used for any prospective booster campaign in the USA are not ideally suited for low-income settings anyway, given that they have to be maintained at temperatures far below freezing. “We should be making more vaccines, and giving away the vaccines that we have bought but cannot use”, he told The Lancet Infectious Diseases. Indeed, a new report from Airfinity, a science information and analytics company, has concluded that global vaccine production will soon reach a level sufficient to cover every adult on the planet. It noted that even if the USA, the UK, the EU, Canada, and Japan vaccinate their entire population older than 12 years and offer booster doses, there would still be a potential surplus of 1·2 billion doses of COVID-19 vaccines by the end of the year. 1·5 billion doses are already being produced every month, and this number is expected to grow. Nonetheless, as things stand, vaccines are not reaching the people most in need. The COVAX facility, a joint endeavour between WHO, Gavi, the Vaccine Alliance, and the Coalition for Epidemic Preparedness Innovations, which aims to ensure equitable global access to the COVID-19 vaccines, has been beset by supply problems. “Instead of planning third doses for people in high-income settings, we should be focusing our attention on the millions of people around the world who are still awaiting their first dose”, said Olivier Wouters, assistant professor of health policy at the London School of Economics and Political Science (London, UK). He added that the potential benefits of booster doses are uncertain, whereas leaving vast swathes of the world's population unvaccinated is sure to lead to more infections, deaths, and troublesome variants. Moreover, there is no guarantee that any immunity conferred by a booster dose will last longer than that offered by the previous doses. The chief executive officers of both Pfizer and Johnson & Johnson have raised the possibility of annual COVID-19 vaccination. Such talk dismays Wouters. “If we get into a mindset where we are thinking about booster doses for richer countries every year, when so many poorer countries have not even covered health-care workers, we really will have failed to meet our obligations to the rest of the world.” Do health-care workers need a COVID-19 vaccine booster?Only a small fraction of people living in low-income countries will have received at least one dose of the SARS-CoV-2 vaccine by the end of 2021. By contrast, booster shots of the mRNA vaccines are being administered in vaccine-rich countries despite an absence of consensus regarding the need for an additional dose.1 Adults working in high-risk settings, including health-care workers, are currently eligible for a COVID-19 vaccine booster in some countries, including the USA, the UK, Germany, and Italy. Full-Text PDF