Decision on booster doses must be evidence-based

Two sides: The biggest argument against booster doses is that of vaccine equity, since even a single dose of a vaccine protects against hospitalisation and death.   | Photo Credit: wildpixel

The SARS-CoV-2 vaccination programme in India began on 16 January, this year. It has been close to eight months since the time individuals who were vaccinated early on received the second dose of the COVID-19 vaccine. This set includes healthcare and other frontline workers, followed by high-risk individuals, including the elderly. Countries such as the U.K., Israel, and the U.S. have started administering booster doses of vaccines, and this has led to the question of whether India should start considering booster doses as well.

Three criteria

For booster doses to be recommended as a policy decision, three criteria need to be met. First, it should be clear that the immunity offered by a vaccine wanes with time, and this results in an increase in the probability of breakthrough infections. Second, for a disease that runs a mild course in a majority of individuals, it should be evident that the lowered efficacy of vaccines with the passage of time is true not only for infection, but also for moderate-to-severe disease necessitating hospitalisation and/or causing death. Third, it is important to prove that the administration of a booster dose reduces the probability of such severe disease, thereby saving lives and reducing the burden on healthcare.

Studies from Israel and the U.S. suggested that the incidence of breakthrough infections increased progressively with the passage of time from the second dose of mRNA vaccines. The study from Israel found this to be true for severe infections as well , with the finding that individuals above the age of 60 were especially vulnerable. A report which analysed the effectiveness of the AstraZeneca Vaxzevria vaccine (which goes by the name of Covishield in India) by Public Health England, found an increased incidence of breakthrough infections after 20 weeks post-vaccination. The effectiveness against hospitalisation and death, though lower, was largely preserved, suggesting that the vaccine continued to be protective against these outcomes. Similar to the mRNA vaccine results, a greater waning of immunity was observed among individuals who were above the age of 65 years and among individuals with underlying medical conditions. While the loss of effectiveness of vaccines against hospitalisations and death are not universally convincing, the data in favour of that being the case for the immunocompromised and the elderly seem consistent.

What is lacking is a biomarker of either cellular and/or antibody mediated immunity which correlates with protection, especially as the former may have an important role to play in long-term protection.

Protective doses

Will the addition of a booster protect against such breakthrough infections, including those that are severe? The results of a study from Israel, although debated for its methodology, seem to suggest that boosters are protective, when given at least 5 months after the initial 2 doses. Whether the same holds true for non-mRNA vaccines is not known. Data from the COV-BOOST trial suggested that an mRNA vaccine resulted in a stronger booster effect no matter what the primary vaccine was, and this was used to guide the Joint Committee on Vaccination and Immunisation (JCVI) recommendations in the U.K.. If India decides to recommend boosters, this data needs to be considered to decide the choice of booster recommended.

The biggest argument against booster doses is that of vaccine equity. It is a known fact that even a single dose of a vaccine protects against hospitalisation and death. In a world in which vaccine shortages have resulted in so many people being left unvaccinated, is it fair to deprive some of protection against hospitalisation and death, while protecting others from an infection that is likely to be mild?

Difficult questions

Even within a country, there are a few difficult questions to be answered. When a common vaccine is used for all age groups, should the first dose of the vaccine for a 15-year old be prioritised over a booster dose for a 65-year old? Or should we prioritize arresting transmission by targeting universal vaccination, as transmission has the potential of selecting newer variants? Should we wait for such newer variants and target specific boosters against them, as is the strategy for an influenza vaccine? Should preventing infections, even mild, among healthcare workers be a priority, considering that they are in close contact with immunosuppressed individuals on a daily basis?

We need data from India to know whether both the available vaccines continue to protect against hospitalisations and death, and whether this is true across all risk groups. In the absence of such data, the extrapolation from studies across the world would suggest that those with immunosuppressive conditions and the elderly might benefit from a booster dose, as has been suggested by the World Health Organization. For the other trade-offs, models that simulate transmission across groups (for example, in schools), hospitalisation rates with varying losses of vaccine effectiveness, and the likely protective effects of boosters in altering such burdens on the healthcare system will be useful to make informed decisions.

Duncan McLaren once stated that “Famine is not caused by a shortage of food; it is caused by a shortage of justice”. Similarly, while many parts of the world wait with eager anticipation for individuals to receive their first dose, it is key that if we recommend booster doses of vaccines, we do it in a way that is just and based on sound scientific principles.

(Lancelot Pinto is a consultant respirologist at P.D. Hinduja National Hospital and Medical Research Centre, Mumbai.)

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Printable version | Dec 7, 2021 5:32:55 AM |

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