You are reading it right, but that’s the wrong chart. That chart is for symptomatic infection. Not really what you care most about.
The data for hospitalization is what you need.
Click on goalie’s link to UK data.
https://assets.publishing.service.g...efing-31-Dec-2021-Omicron_severity_update.pdf
Page 12. It puts the booster at 88% effective against hospitalization.
“These estimates suggest that vaccine effectiveness against symptomatic disease with the Omicron variant is significantly lower than compared to the Delta variant and wanes rapidly. Nevertheless, protection against hospitalisation is much greater than that against symptomatic disease, in particular after a booster dose, where vaccine effectiveness against hospitalisation is close to 90%.”