12 January 2023 Blog Post: On COVID Boosters
It is a question I get a lot these days – “How is the bivalent booster working?”
Not well is the answer.
Without even delving into the immunogenicity and efficacy data, the booster isn’t working well simply when its most important metric – uptake. To date, an abysmal 15.4% of the population eligible for the bivalent booster have received it (link: https://covid.cdc.gov/covid-data-tracker/#datatracker-home).
A critical fraction of individuals must be vaccinated in order to either control or eradicate an infection with a specific base reproductive ratio (remember in 2020 when we were talking about R-naught / R0?). For disease with high transmission potential, the vaccination fraction would be higher than for those diseases with lower transmission potential. Generally the R0 of COVID is felt to be between 1.8 and 2.5 which would mean that about 40-50% of the population would need to be vaccinated to make an appreciable difference in transmission rates.
In a concise and readable format, Dr. Paul Offit from the Vaccine Education Center at UPenn, details the “underwhelming” immunity response derived from the bivalent boosters (link: https://www.nejm.org/doi/full/10.1056/NEJMp2215780) suggesting that booster dosing is ‘probably best reserved for the people most likely to need protection against severe disease.” He argues against boosting healthy young people with “vaccines containing mRNA from strains that might disappear a few months later.”
And, in fact, the public would agree – even Maine which has amongst the highest booster vaccination rates in the US. By age group (link:https://covid.cdc.gov/covid-data-tracker/#vaccinations_vacc-people-booster-percent-pop65):
Age Group Percentage of Population with Updated Booster Dose
5+: 28.5%
12+: 30.2%
18+: 31.7%
65+: 63.6%
But, with all due respect to Dr. Offit, this isn’t really public health policy – all he has done is held up a reflective glass to the actual population trend (and supported such with immunologic data). But kudos for dealing with reality.
A more effective public health strategy, I would argue, would be to boost the population (with priority to those most susceptible to severe disease) with vaccines containing mRNA from strains that will appear. We already do this for influenza wherein the components of the annual flu shot are based upon data from 144 national influenza centers in over 114 countries that conduct year-round surveillance for flu viruses. Vaccine components are selected based upon which viruses are making individuals sick, the extent to which those viruses are spreading prior to the upcoming season and how well the previous year’s vaccine might protect against such. A combination of active surveillance and retrospective analysis of the variants that have emerged (alpha, delta, BA.1, BA.4, BA.5) would be our best chance of developing a more effective, longer lasting booster.
𝗦𝗶𝗴𝗻 𝗨𝗽 𝗳𝗼𝗿 𝗢𝘂𝗿 𝗡𝗲𝘄𝘀𝗹𝗲𝘁𝘁𝗲𝗿
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