The following is a summary of “Protection Conferred by Delta and BA.1/BA.2 Infection Against BA.4/BA.5 Infection and Hospitalization: A Retrospective Cohort Study,” published in the March 2023 issue of Infectious Diseases by Winchester, et al.

The decline in immunity against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and the emergence of viral mutations have raised concerns about immune escape. In vitro, studies have highlighted the potential for immune escape by the BA.4/BA.5 variant, but its real-world impact is still being determined.

The retrospective cohort study included 20,987 individuals tested for COVID-19 by polymerase chain reaction during the Delta or BA.1/BA.2 waves and retested during the BA.4/BA.5 wave. The study calculated the preventable fraction (PF), the ratio of infection to hospitalization rate for initially positive patients divided by the ratio for initially negative patients. The PF was stratified by age and adjusted for age, sex, comorbidities, and vaccination status using logistic regression.

In 20,987 patients, prior infection with Delta provided minimal protection against hospitalization (PF = 10.7%, 95% CI: 4.9%–21.7%; P = .003) and no protection against BA.4/BA.5 infection (PF = 11.9%, 95% CI: .8%–21.8%; P = .04). In contrast, prior BA.1/BA.2 infection provided 45.9% protection against BA.4/BA.5 reinfection (95% CI: 36.2%–54.1%; P < .001) and 18.8% protection against hospitalization (95% CI: 10.3%–28.3%; P < .001). Up-to-date vaccination provided modest protection against BA.4/BA.5 reinfection and hospitalization.

The study suggested prior infection with BA.1/BA.2 and up-to-date vaccination offered modest protection against BA.4/BA.5 infection and hospitalization. However, prior Delta infection provided minimal protection against hospitalization and no protection against BA.4/BA.5 infection.

Reference: academic.oup.com/jid/article/227/6/800/6982684