A Comirnaty booster dose given to those aged 50 years and over provides >90% vaccine effectiveness against COVID-19 infection
A Comirnaty booster dose in those over the age of 50 provides a greater than 90% vaccine effectiveness, irrespective of whether individuals had been previously fully vaccinated with ChAdOx1-S (AstraZeneca) or Comirnaty (BNT162b). This was the finding of a study by a team from the UK Health Security Agency, UK, which is available online but not published in a peer-reviewed journal.
With evidence that the efficacy of COVID-19 vaccines wanes 20 weeks after vaccination, the Joint Committee on Vaccination and Immunisation (JCVI) in the UK issued a statement highlighting the need for a booster dose of COVID-19 vaccines in an effort to combat the virus during the winter months. Moreover, after a review of the available data on booster responses, the JCVI advised a preference for the Comirnaty vaccine as the booster dose irrespective of which product was used to provide the initial full vaccination.
In the present study, the UK team sought to estimate the real-world effectiveness of a single Comirnaty booster dose in those aged 50 years and older. The researchers compared vaccination status in this patient cohort, who were symptomatic for COVID-19 and with a positive PCR test result. Data was obtained from the National Immunisation Management System (NIMS) and a booster dose was defined as one given 140 days or more after a second vaccination dose. Vaccine effectiveness was adjusted in regression models for age, deprivation, ethnicity, care home residence status and co-morbidities. The analysis was also stratified by the primary vaccination received, i.e., either ChAdOx1-S (AstraZeneca) or Comirnaty and vaccine effectiveness assessed at several time points e.g., 2 to 6 days post booster dose and 14 or more days later.
For the primary analysis, the team compared vaccine effectiveness in those who received a booster with those who had been fully vaccinated but without a booster dose. In a secondary analysis, they determined the absolute vaccine effectiveness which was the difference in rates of infection between those who had two doses (at least 140 days apart) and a booster with those who were unvaccinated.
There were 271,747 eligible tests in people 50 years and older, of which 13,568 (5%) were unvaccinated with the remainder being fully vaccinated with either ChAdOx1-S or comirnaty (BNT162b)
The vaccine effectiveness from a BNT162b booster in those who were fully vaccinated with ChAdOx1-S was 87.4% (95% CI 84.9 – 89.4) and 84.4% (95% CI 82.8 – 85.8%) in those fully vaccinated with BNT162b.
In the secondary analysis, compared with unvaccinated individuals, those fully vaccinated with a primary course of ChAdOx1-S had an absolute vaccine effectiveness of 93.1% (95% CI 91.7 – 94.3%) and 94% (95% CI 93.4 – 94.6%) in those fully vaccinated with BNT162b.
Interestingly, when compared with those who were fully vaccinated but had not received a booster dose, the vaccine effectiveness after 20 or more weeks was 44.1% for the ChAdOx1-S vaccine and 62.5% for BNT162b.
In their conclusion, the authors wrote ‘our study provides real world evidence of significant increased protection from the booster dose against symptomatic disease in those aged over 50 years of age irrespective of which primary course was received.’