Bivalent mRNA booster vaccine reduces risk of severe COVID-19 by more than half: CDC

USA: Updated bivalent (two-strain) mRNA booster shots reduce the risk of contracting severe COVID-19 by up to 57%, a recent study in Morbidity and Mortality Weekly Report (MMWR) has stated. The updated booster shots target the Omicron BA.4/BA.5 sublineages of COVID-19 and the original strain. 

A second study also published in MMWR revealed that bivalent boosters effectively prevent hospitalizations in elderly Americans. 

In the first study, Mark W. Tenforde, National Center for Immunization and Respiratory Diseases, CDC, and colleagues aimed to calculate vaccine effectiveness (VE) from Sep 13 to Nov 18 using data from the VISION Network. They compared the vaccine effectiveness of a bivalent mRNA booster dose (after 2, 3, or 4 monovalent [one-strain] doses) versus no previous vaccination and previous receipt of 2, 3, or 4 monovalent-only mRNA vaccine doses in adults aged 18 years or older with an emergency department/urgent care (ED/UC) visit or hospitalization for a COVID-19–like illness.

The study included a total of 78,303 ED/UC encounters with COVID-19–like illness, and the authors identified 12% (n=9,009) case-patients and 89% control (n=69,294). Overall, 31% were unvaccinated, and only 5% of adults received a bivalent booster dose, 6% (n=216) had received two monovalent doses, 43% (n=1,679) had received three monovalent doses, and 51% (n=2,010) had received four monovalent vaccine doses. 

The findings of the study were as follows:

"In the early study of immunocompetent adults, we found significant protection from a booster dose of bivalent mRNA COVID-19 vaccine (following receipt of 2, 3, or 4 monovalent doses) versus no vaccination," the researchers wrote. "We also found significant relative benefits of a bivalent booster dose compared with the previous receipt of monovalent doses only." 

"If eligible, all persons should stay up to date with recommended COVID-19 vaccinations, including receiving a bivalent booster dose," they concluded. 

The second study included data from 22 hospitals in 18 states who were the participants of the IVY Network. The bivalent booster dose offers even more protection to adults aged 65 and above without compromised immune systems. 

Diya Surie, National Center for Immunization and Respiratory Diseases, CDC, and colleagues estimated VE against COVID-19–associated hospitalization by comparing the odds of bivalent booster dose receipt with no COVID-19 vaccination between case patients and control patients in the test-negative study.

A total of 798 adults (381 case patients and 417 control patients) were included in the analysis from Sep 8 and Nov 30; the median age was 76 years. 74% of participants had underlying health conditions.

Of the 381 case patients, 21% (n=81) were unvaccinated, 73% (n=280) had received 2 or more monovalent-only mRNA vaccine doses, and 5% (n=20) had received a bivalent booster dose. Among controls, 14% had been boosted with a bivalent vaccine. 

"Vaccine effectiveness of a bivalent booster dose compared with unvaccinated patients for the prevention of COVID-19–associated hospitalization was 84%," the authors wrote. "Relative VE of a bivalent booster dose was 73% compared with patients who had received ≥2 monovalent-only mRNA vaccine doses ≥ two months before illness onset."

The findings reinforce the importance of bivalent boosters for older adults at maximum risk for severe outcomes of COVID-19 infections. 

To maximize protection against severe COVID-19, all eligible individuals, particularly adults aged ≥65 years, should receive a bivalent booster dose and practice additional prevention strategies, such as masking in indoor public spaces.

References:

1) Tenforde MW, Weber ZA, Natarajan K, et al. Early Estimates of Bivalent mRNA Vaccine Effectiveness in Preventing COVID-19–Associated Emergency Department or Urgent Care Encounters and Hospitalizations Among Immunocompetent Adults — VISION Network, Nine States, September–November 2022. MMWR Morb Mortal Wkly Rep. ePub: 16 December 2022. DOI: http://dx.doi.org/10.15585/mmwr.mm715152e1

2) Surie D, DeCuir J, Zhu Y, et al. Early Estimates of Bivalent mRNA Vaccine Effectiveness in Preventing COVID-19–Associated Hospitalization Among Immunocompetent Adults Aged ≥65 Years — IVY Network, 18 States, September 8–November 30, 2022. MMWR Morb Mortal Wkly Rep. ePub: 16 December 2022. DOI: http://dx.doi.org/10.15585/mmwr.mm715152e2