Immunocompromise among vaccinated versus unvaccinated COVID-19 cases admitted to critical care in Ireland, July to October 2021.

As the COVID-19 pandemic progressed, so too did the proportion of cases admitted to critical care in Ireland who were fully vaccinated. Reporting of this observation has public health implications as incorrect interpretation may affect public confidence in COVID-19 vaccines. A potential explanation is the reduced ability of those who are immunocompromised to produce an adequate, sustained immune response to vaccination. We conducted an analysis of the association between COVID-19 vaccination status and underlying degree of immunocompromise among a cohort of critical care patients all with a confirmed diagnosis of COVID-19 admitted to critical care between July and October 2021. Multinomial logistic regression was used to estimate an odds ratio of immunocompromise among vaccinated COVID-19 cases in critical care compared to unvaccinated cases. In this study, we found a statistically significant association between the vaccination status of severe COVID-19 cases requiring critical care admission and underlying immunocompromise. Fully vaccinated patients were significantly more likely to be highly (OR = 19.3, 95 % CI 7.7-48.1) or moderately immunocompromised (OR = 9.6, 95 % CI 5.0-18.1) compared to unvaccinated patients with COVID-19. These findings support our hypothesis, that highly immunocompromised patients are less likely to produce an adequate and sustained immune response to COVID-19 vaccination, and are therefore more likely to require critical care admission for COVID-19 infection.