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Written by: Dr David Owens 
The WHO expert committee advised booster shots for anyone over the age of 60 who received inactivated vaccines, such as Sinovac. They also advised boosters for anyone that is immunocompromised. The Hong Kong expert committee has advised booster shots for high-risk groups, anyone aged 60 and above and those who have received Sinovac. The government recently announced that boosters will be available from the first week in January 2022 for anybody over the age of 18 who has had their second shot more than six months previously.
The risk-benefit for vaccination, including the need for booster shots and the indications for vaccinating children change depending on the current public health strategy. Essentially both are less urgent in the context of a zero Covid policy. The recent Omicron variant has shifted this dynamic. The increasing infectivity and the expectation of a large international wave of infections tips the balance in favour of earlier booster vaccination. OT&P currently advise booster shots for our patients as soon as they become eligible. Eligibility information is available here and you can make a booking here.
So, are Covid booster shots a good idea?
Answer: Yes
The evidence for both population effectiveness and antibody response for the mRNA vaccines is excellent. We know that BioNTech vaccine is significantly more effective than Sinovac in terms of the generated antibody response[2] ,from a population perspective it would be best if Hong Kong has as high levels of immunity as possible.
We have good evidence from international studies that booster shots do not just restore the immunity which develops after the initial two shots. A booster shot has been shown to significantly improve both antibody response but also T cell and memory cell immunity. In some ways, there is an argument to say that the third shot is not technically a booster. Rather that the Covid vaccines require three shots for optimal immunity.
In summary, we now have very good evidence about the effectiveness of different vaccines. We are beginning to accumulate evidence around which vaccines produce a better immune response, which vaccines are most effective against evolving variants and importantly we are beginning to explore the optimal dose and timing between doses to provide population benefit. There is incontrovertible evidence that vaccinations save lives, reduce the severity of severe illness, reduce the incidence of Long Covid and protect health systems. The challenge for Hong Kong is to maximise population immunity especially from the vulnerable down by widespread use of vaccinations including booster doses.
References
1. Cowling, B. J., Lim, W. W., & Cobey, S. (2021, July 5). Fractionation of COVID-19 vaccine doses could extend limited supplies and reduce mortality. Nature News. https://www.nature.com/articles/s41591-021-01440-4.
2. Lim, W. W., Mak, L., Leung, G. M., Cowling, B. J., & Peiris, M. (2021, July 15). Comparative immunogenicity of mRNA and inactivated vaccines against COVID-19. https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(21)00177-4/fulltext.
