Severe COVID-19 has been successfully protected against by monovalent vaccinations based on the ancestor strain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

The effectiveness and longevity of vaccination protection, however, have been reduced by the appearance of mutant variations with immune-evasive features. A number of nations have frequently developed booster programs to safeguard vulnerable (sub)populations.

There are now bivalent vaccinations that target the ancestral and Omicron spike proteins. Research revealed that bivalent vaccinations improved SARS-CoV-2 Omicron BA.2.75, BA.4, and BA.5 neutralizing capacity.

Researchers in the current study assessed the efficiency of bivalent immunizations against COVID-19-related hospitalization in England as well as the long-term protection provided by monovalent vaccines. A test-negative case-control design was used.

In order to gauge the duration, the study periods were September 5, 2022, to February 5, 2023 and June 13, to December 25, 2022.of defense with monovalent vaccines and the effectiveness of bivalent booster immunization, respectively.

It was determined when the most recent positive test occurred during the research period(s). Cases other than Omicron were not included. The National Immunization Management System was connected to the COVID-19 testing data (NIMS).

The NIMS was used to retrieve information on immunization, sex, age, ethnicity, risk group status, immunosuppression, clinically highly vulnerable status, and status as a social or healthcare worker.

The Secondary Uses Service was used to find acute respiratory illness inpatient admissions, and the testing data were linked to them.

To gauge the effectiveness of the vaccination against serious disease outcomes, SARS-CoV-2 testing were limited to patients requiring supplemental oxygen, critical care, or mechanical ventilation.

Test results and vaccination status were employed as the outcome and key variables, respectively, in multivariate logistic regression. The increased vaccination efficacy (iVE) of the fourth dose was estimated relative to the last third received at least six months before the sample date in people aged 75 or older.

The iVE of the bivalent booster was estimated in those who were at least double-vaccinated before September 5, 2022, and six months before the test date.