Vaccination against SARS-CoV-2 has helped protect many people against Covid-19 as well as prevent the spread of infection to others. It has also reduced the severity of infection in those unfortunate enough to be reinfected with the coronavirus by ensuring that a lower viral load after reinfection significantly reduces the need for hospitalisation and the likelihood of subsequent death. “Breakthrough infections” in those fully vaccinated against Covid-19 appear to be the result of waning vaccine efficacy after six months, coupled with the reduced efficiency of existing vaccines against the newer Delta variant, and possibly other emerging variants, of the virus. As with some other vaccines, levels of protective ‘neutralising’ antibodies inevitably fall with time and Covid vaccination does not ensure long-term protection.
One time-tested approach to prevent reinfection with the same organism makes use of booster vaccines, which stimulate antibody-producing B cells and thereby lead to a protective spike in circulating antibody levels. There is some evidence that this approach may also apply to SARS-Cov-2. In Israel, scientists at Kahn Sagol Maccabi, the research and innovation centre of health-maintenance organisation Maccabi Healthcare Services (MHS) in Tel Aviv, studied the health records of 1,352,444 eligible MHS members over the age of 16 who received the second dose of vaccine between January and April 2021. They showed that reinfections were commoner in those vaccinated earlier, whose antibody levels were in decline. Maccabi’s subsequent survey of 149,144 recipients of a booster vaccine, aged 60 and over, documented 37 positive tests, while 1,064 positives were noted in a control (or comparison) group of 675, 630 who received a second dose of vaccine in January or February 2021. This represents an 86 per cent effectiveness in preventing infection with Covid-19 on a second occasion. Similar findings have been noted among people logging into the ZOE Covid Symptom Study app in the UK from 11 December 2020, which monitors the efficacy and side-effects of vaccination.
Following the example of Israel, where a third vaccine for older citizens was introduced on 29 July 2021, several other countries, including the US, UK, France, Germany, and the United Arab Emirates have recently announced plans to implement booster vaccination programmes. On 12 August 2021, the FDA in the US accordingly authorised third doses of Pfizer/BioNTech or Moderna vaccines for certain groups of immunocompromised patients.
A planned Covid-19 booster programme in the NHS will involve administration of simultaneous booster Covid vaccines and annual flu jabs to a prioritised group, over 15 weeks, between 6 September and 17 December 2021. This group potentially includes all adults aged 70 and over, residents in residential care homes for older adults, and younger adults (aged 16 and over) who are either immunosuppressed or considered clinically extremely vulnerable. The precise details of who receives the booster and when are yet to be finalised. On completion of the first phase of this programme, booster vaccines may also be offered to all adults aged 50 years and over, adults aged 16 to 49 who are at risk for Covid-19 or flu, and those living in the same house as immunocompromised people. In the UK, it also seems likely that different vaccines will be mixed in a belief that this may further enhance protection-supportive evidence from the Cov-Boost study is awaited. This British study is currently evaluating seven different Covid-19 vaccines, given at least 10 to 12 weeks after a second dose.
As people in several richer countries become eligible for a third, or booster, vaccine, many in poorer countries have yet to receive their first dose. In an attempt to better share out available resources and to even out global disparities arising from inequities in vaccine distribution, the World Health Organisation (WHO) called, on 4 August 2021, for a moratorium on boosters until at least the end of September so that more people can share in the benefits of vaccination. The waning influence of WHO makes it likely that this call to redistribute vaccines will largely fall on deaf ears.
While the end may seem near, the vaccination programme continues to evolve in response to fresh challenges. The coronavirus has proved to be a wily as well as a deadly foe, having recruited human support in the form of Covid-deniers and anti-vaxxers as it continues to stave off eventual defeat. In the interim, the desirability of booster vaccine initiatives awaits confirmation and the diversion of booster vaccines to help those as yet unvaccinated remains a possible option.
Ashis Banerjee