Cancer patients are at high risk for severe COVID-19, making extra vaccine doses important. This study assessed their effectiveness using real-world data.
In the monovalent booster period (up to August 2022), an additional dose reduced hospitalizations (29.2% effectiveness), with rates of 30.5 per 1,000 person-years in boosted patients compared to 41.9 in those with only the primary series. The number needed to vaccinate (NNV) to prevent one hospitalization was 166. ICU admission was reduced by 35.6%. In the general population, effectiveness was higher (50.8% for hospitalization), but the NNV was much larger (1,107) due to lower baseline risk.
In the bivalent vaccine period (September 2022–August 2023), effectiveness against hospitalization was 29.9%, with rates of 13.4 per 1,000 person-years in vaccinated patients versus 21.7 in unvaccinated. The NNV was 451. ICU admission was reduced by 39.4%.
Overall, extra doses significantly lowered hospitalization and ICU admission risk for cancer patients, though protection against infection itself was limited.