Study: Effectiveness of the Bivalent mRNA Vaccine in Preventing Severe COVID-19 Outcomes: An Observational Cohort Study. Image Credit: Parilov/Shutterstock

Real-world efficacy of a bivalent vaccine to prevent COVID-19 hospitalizations in non-hospitalized subjects

In a recent study published on Preprints by Lancet*researchers investigated the efficacy of a bivalent messenger ribonucleic acid (mRNA) booster of the 2019 coronavirus (COVID-19) vaccine in preventing severe outcomes from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections.

Study: Efficacy of Bivalent mRNA Vaccine in Preventing Severe Outcomes of COVID-19: An Observational Cohort Study. Image credit: Parilov/Shutterstock


While early monovalent COVID-19 vaccines were highly effective in reducing the severity of SARS-CoV-2 infections, the emergence of Omicron subvariants calls into question the efficacy of these vaccines.

Omicron subvariants carry mutations that increase their ability to evade vaccine-induced immunity and previous SARS-CoV-2 infections. These mutations are largely in the spike-protein region, which is also the target of most neutralizing antibodies induced by monovalent vaccines.

Recently developed bivalent mRNA vaccines contain mRNA sequences that encode components of the SARS-CoV-2 ancestral strain and one of the newer Omicron subvariants, such as BA.4/BA.5.

In late August 2022, the United States Food and Drug Administration (FDA) approved Pfizer-BioNTech and Moderna’s bivalent mRNA vaccines as booster doses for adults with complete primary vaccination. Approval was granted based on the efficacy of monovalent vaccines and the safety and immunogenicity of bivalent vaccines.

Israel has approved the administration of booster doses of the bivalent vaccine to people at high risk of contracting COVID-19, especially people over 65 years of age. While some studies have examined the effectiveness of bivalent vaccines in preventing severe disease from COVID-19 in hospitalized individuals, the effectiveness of these vaccines in preventing serious outcomes such as hospitalization and death in non-hospitalized individuals remains unclear.

About studying

In this study, researchers performed a retrospective cohort analysis of medical health records obtained from Clalit Health Services, which includes medical data on nearly two-thirds of the Israeli population over the age of 65. Participants were offered the Pfizer-BioNTech bivalent mRNA vaccine and were followed for at least two weeks after vaccination.

The primary and secondary endpoints measured during the study were COVID-19-related hospitalization or death. Demographic information such as age, socioeconomic status, etc. were extracted, as well as data on history of vaccination against COVID-19, type of primary vaccination, results from polymerase chain reaction (PCR) or antigen tests, history of hospitalization and death. from the medical records.

Additionally, additional information was obtained on risk factors for COVID-19 such as asthma, chronic obstructive pulmonary disease, chronic kidney disease, chronic heart failure, diabetes mellitus, hypertension, lung cancer, coronary heart disease, obesity, and smoking.

The association between severe COVID-19 outcomes and bivalent vaccine boosters was analyzed using a Cox proportional hazard regression model adjusting for comorbidities and demographic factors.


Results indicated that 14% (85,314) of 622,701 eligible participants received a bivalent mRNA booster. Hospitalization related to COVID-19 was required for only six recipients of the bivalent vaccine, compared with 297 who did not receive a booster dose of the bivalent vaccine and were hospitalized for COVID-19. The incidence of death among recipients of the bivalent vaccine was also significantly lower than among those who did not receive the bivalent vaccine (one vs. 73).

Factors such as male gender and increasing age were associated with a higher risk of hospitalization related to COVID-19, and comorbidities such as chronic heart failure, chronic renal failure, cerebrovascular accident, and chronic obstructive pulmonary disease also increased the risk of hospitalization. after SARS-CoV-2 infection. Risk factors for COVID-19-related death were similar except for male gender, which was not associated with a high risk of COVID-19-related mortality.

Despite the efficacy of the bivalent vaccine, its uptake as a booster has been significantly low, with less than 14% of the eligible population using the vaccine. The authors believe that the low uptake rate could be due to misconceptions about the vaccine, such as side effects or misinformation that previous doses of the vaccine or SARS-CoV-2 infection are sufficient to protect against future infections.


Overall, the results showed that a booster dose of the bivalent mRNA vaccine significantly reduced the risk of hospitalization and death related to COVID-19 by 81% and 86%, respectively.

Amidst the growing number of breakthrough infections arising from Omicron subvariants, these findings highlight the importance of making a bivalent vaccine available to those at high risk of COVID-19, such as the elderly population and individuals with comorbidities.

*Important notice

Preprints with the Lancet publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guiding clinical practice/health-related behaviour, nor should they be treated as verified information.

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