Updated bivalent mRNA booster protects against circulating SARS-CoV-2 variants

In a recent Morbidity and Mortality Weekly Report published by the United States Centers for Disease Control and Prevention (CDC), researchers discuss the efficacy of the bivalent coronavirus disease 2019 (COVID-19) vaccine against symptomatic infection with several SARS-CoV-2 variants that are currently circulating throughout the U.S.

Study: Early Estimates of Bivalent mRNA Booster Dose Vaccine Effectiveness in Preventing Symptomatic SARS-CoV-2 Infection Attributable to Omicron BA.5- and XBB/XBB.1.5-Related Sublineages Among Immunocompetent Adult s- Increasing Community Access to Testing Program, United States, December 2022-January 2023. Image Credit: PeopleImages.com – Yuri A / Shutterstock.com

SARS-CoV-2 Omicron subvariants

Since the emergence of the wild-type strain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) at the end of 2019, which subsequently led to the COVID-19 pandemic, several SARS-CoV-2 variant strains have emerged. The SARS-CoV-2 Omicron variant, for example, was originally detected in Botswana and South Africa in late November 2021.

Since then, the Omicron variant has further mutated into several subvariant strains, the most recent of which includes XBB and XBB.1.5. In the United States, the Omicron subvariant XBB was originally detected in August 2022; however, by late December 2022, XBB.1.15 was identified as the dominant circulating strain of SARS-CoV-2, with over 50% of sequenced samples testing positive for this subvariant.

About the study

In an effort to mitigate the spread of SARS-CoV-2, several COVID-19 vaccines have been developed and administrated to people around the world. Unfortunately, the emergence of mutated SARS-CoV-2 variants has reduced the efficacy of current COVID-19 vaccines against infection with certain variants. As a result, researchers have updated the original COVID-19 vaccines, which were previously targeted against the wild-type strain of SARS-CoV-2, to also incorporate the genetic material of the SARS-CoV-2 Omicron variant.

In the current study, the vaccine effectiveness (VE) of the updated Pfizer-BioNTech bivalent messenger ribonucleic acid (mRNA) COVID-19 vaccine was estimated against symptomatic infection caused by Omicron BA.5, XBB, and XBB.1.5 infections in immunocompetent adults. Whereas BA.5 infection was identified upon the reduction or failure of the SARS-CoV-2 spike gene (S-gene) amplification (SGTF) in real-time reverse transcription-polymerase chain reaction (RT-PCR), XBB/XBB.1.15 infection was confirmed by S-gene target presence (SGTP).

Increasing dominance of XBB.1.5

A total of 29,175 nucleic acid amplification tests (NAATs) were obtained from adults who had previously received between two and four doses of the original COVID-19 vaccine dose, 8,358 of whom had also received a bivalent booster dose two to three months prior to their NAAT.

All adults who participated in the current study had reported one or more COVID-19-like symptoms at the time of their NAAT. Taken together, 47% of the study participants tested positive for SARS-CoV-2, 78% and 22% of whom were infected with BA.5 or XBB/XBB.1.5 subvariants, respectively.

Between December 1, 2022, and January 2, 2023, 33% of the samples that tested positive for SARS-CoV-2 were of the XBB.1.5 lineage, with over 50% accounting for XBB/XBB.1.5. However, when this 30-day period was separated into shorter intervals, the researchers found that XBB.1.5 prevalence increased from 33% to 38% between December 11-January 2, and 43% between December 18, 2022, and January 2, 2023.

Bivalent mRNA vaccine protects against symptomatic infection

About 34% of patients who tested negative for SARS-CoV-2 had previously received a bivalent COVID-19 mRNA booster vaccine dose as compared to those who tested positive. Of those who tested positive for SARS-CoV-2, the VE of the bivalent vaccine was similar against BA.5 and XBB/XBB.1.15 infections.

When considering age, the bivalent COVID-19 mRNA vaccine was 52% effective against symptomatic infection in adults between 18 and 49 years of age, 43% effective in those aged 50-64, and 37% effective in those over the age of 65. Notably, this VE did not appear to wane three months after vaccination in individuals who had previously received two, three, or four doses of the original monovalent COVID-19 vaccine.

Conclusions

The current study finding support current recommendations by the United States CDC to continue to provide bivalent immunization to the public. As SARS-CoV-2 variants continue to emerge, it is increasingly important for public health officials to monitor the VE of both monovalent and bivalent COVID-19 vaccines.