28 Augustus 2022 Addendum to Episode 284 on effect of variant booster

Addendum to Ep 284 on discussion about adapted vaccines

Ep 284-13: David Khoury medRxiv 26 Aug 2022 Predicting the efficacy of variant-modified COVID-19 vaccine boosters

This paper is based on 2 sources

• the various recent preprints comparing increase in neutralization titers after booster with ancestral or variant-specific boosters.
• the previous work by Khoury where the relation between neutralization titers and protection against infection and disease was calculated, based on original phase 3  trials.  

Findings:

1. Neutralisation titers increase after booster with

• Ancestral strain = 11 X
• Variant strain = 16.6 X ( = 1.51 X more than ancestral
• No significant difference in homologous versus non-homologous variant   

2. Clinical protection: in a population that is still 50 % protected against symptomatic infection and 86.6 % against severe disease because of previously acquired immunity (by vaccination and/or infection).

Additional protection by booster:

• Against symptomatic disease
  • Ancestral booster: 50 → 85.6 %
  • Variant booster: 50 → 90.2 %
• Against severe disease
  • Ancestral: 86.6 → 98 %
  • Variant: 86.6 → 98.8 %   

If the basal level of protection is lower (because of waning) the additional gain of a booster is higher (up to 15 % ) and the difference between variant or ancestral booster is more important

Conclusion:

• The main gain is by booster, but an additional gain from variant specific booster
• The importance of this additional gain depends on the basal immunity

Clearly, this modeling needs to be confirmed in clinical trials / observations

It applies only on the presently known variants.