Breakthrough Cases of COVID in Those Who Are Immunocompromised

July 21, 2021

The European Society of Clinical Microbiology and Infectious Diseases published the results of a retrospective study of 17 hospitals throughout Israel. The study included 152 patients who tested positive for COVID-19 after being fully vaccinated with the Pfizer vaccine (breakthrough cases) and required hospitalization. This study aimed to “characterize vaccinated patients with breakthrough COVID-19 requiring hospitalization and define the main risk factors associated with poor outcomes in this group.” Notably, 40% of breakthrough cases included patients who were immunocompromised. 

Real-world data coming from Israel’s mass vaccination campaign parallel Phase 3 clinical trial data, supporting Pfizer vaccine’s 95% efficacy rate. That being said, efficacy was shown to be lower in those with multiple comorbidities and the immunocompromised. The most common causes of immunosuppression included chronic corticosteroid treatment, antimetabolite therapy, and anti-CD20 treatment (Rituximab, commonly used to treat rheumatoid arthritis, is an anti-CD20 biologic agent).

Overall, “comorbidities were more common in patients with vaccine breakthrough infections compared with large case series on unvaccinated hospitalized patients.” This reconfirms the hypothesis that the vaccine elicits a lower efficacy rate amongst those with certain comorbidities, especially if they are on immunosuppressive therapies. “Immunosuppression was not associated with a worse outcome, except for anti-CD20 treatment, which had a threefold higher odds ratio to be in the poor outcome group (13% versus 4%).” The overall mortality rate amongst these cases paralleled unvaccinated hospitalized COVID-19 patients.