In a recent Weekly report on morbidity and mortality published by the US Centers for Disease Control and Prevention (CDC), researchers discuss the efficacy of the 2019 bivalent coronavirus disease (COVID-19) vaccine against symptomatic infection with several SARS-CoV-2 variants currently circulating in the US
Study: Early Estimates of Bivalent mRNA Booster Dose Vaccine Efficacy in Preventing Symptomatic SARS-CoV-2 Infection Attributable to Omicron BA.5 and XBB/XBB.1.5 Related Sublines 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 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019, which subsequently led to the COVID-19 pandemic, several variants of SARS-CoV-2 have emerged. For example, the SARS-CoV-2 Omicron variant was first detected in Botswana and South Africa at the end of 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 discovered in August 2022; however, in late December 2022, XBB.1.15 was identified as the dominant circulating strain of SARS-CoV-2, with more than 50% of samples sequenced testing positive for this subvariant.
About the study
To combat the spread of SARS-CoV-2, several COVID-19 vaccines have been developed and administered to people around the world. Unfortunately, the emergence of mutated SARS-CoV-2 variants has reduced the effectiveness of current COVID-19 vaccines against infection with certain variants. As a result, researchers have updated the original COVID-19 vaccines, which previously targeted the wild-type strain of SARS-CoV-2, to also include 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 . While BA.5 infection was identified after 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, of whom 8,358 had also received a bivalent booster dose two to three months prior to their NAAT.
All adults enrolled in the current study had reported one or more COVID-19-like symptoms at the time of their NAAT. Overall, 47% of study participants tested positive for SARS-CoV-2, of whom 78% and 22% were infected with BA.5 or XBB/XBB.1.5 subvariants, respectively.
Between December 1, 2022 and January 2, 2023, 33% of samples that tested positive for SARS-CoV-2 were of the XBB.1.5 line, of which more than 50% were XBB/XBB.1.5. However, when this 30-day period was broken down into shorter intervals, the researchers found that the prevalence of XBB.1.5 increased from 33% to 38% between December 11 and January 2, and 43% between December 18, 2022 and January 2, 2023.
Bivalent mRNA vaccine protects against symptomatic infection
Approximately 34% of patients who tested negative for SARS-CoV-2 had previously received a bivalent dose of COVID-19 mRNA booster vaccine compared to those who tested positive. Among 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.
In terms of age, the bivalent COVID-19 mRNA vaccine was 52% effective against symptomatic infection in adults aged 18-49, 43% effective in those aged 50-64, and 37% effective in those over 65 years of age. In particular, this VE did not appear to decrease three months after vaccination in subjects who had previously received two, three or four doses of the original monovalent COVID-19 vaccine.
The current study finding supports current recommendations from the US CDC to continue providing bivalent immunization to the public. As SARS-CoV-2 variants continue to emerge, it is becoming increasingly important for public health officials to monitor the VE of both monovalent and bivalent COVID-19 vaccines.
- Link-Gelles, R., Ciesla, AA, Roper, LE, et al. (2022). Early Estimates of Bivalent mRNA Booster Dose Vaccine Efficacy in Preventing Symptomatic SARS-CoV-2 Infection Attributable to Omicron BA.5 and XBB/XBB.1.5 Related Sublines Among Immunocompetent Adult s- Increasing Community Access to Testing Program, United States, December 2022-January 2023. Weekly report on morbidity and mortality. doi:10.15585/mmwr.mm7205e1. https://www.cdc.gov/mmwr/volumes/72/wr/mm7205e1.htm