Bivalent boosters provide additional protection from BA.5, XBB and XBB.1.5

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at recent days Morbidity and Mortality Weekly Report (MMWR) Published on the website of the US Centers for Disease Control and Prevention (US-CDC), researchers analyzed data from Increasing Community Access to Tests (ICATT), a nationwide pharmacy program run in the US to treat SARS-CoV-2. 2 (SARS-CoV-2) test.

They made preliminary estimates of coronavirus disease 2019 (COVID-19) against symptomatic infection by bivalent mRNA-associated subvariants (updated). The study period was December 1, 2022 and January 13, 2023.

Study: Early Estimates of Efficacy of a Bivalent-Dose mRNA Booster Vaccine in Preventing Symptomatic SARS-CoV-2 Infection Attributable to Omicron BA.5 and XBB/XBB.1.5-Related Sublines Among Immunocompetent Adults Increased Community Access to Testing Program, US, December 2022 - January 2023. Image Credit: Cryptographer/Shutterstock

Stady: Early Estimates of Efficacy of a Dual-dose mRNA Booster Vaccine in Preventing Symptomatic SARS-CoV-2 Infection Attributed to Omicron BA.5 and XBB/XBB.1.5-Related Sub-Threads Among Immunocompetent Adults Increased Community Access to Testing Program, States United, December 2022 – January 2023. Image credit: Cryptographer/Shutterstock

background

The XBB and XBB.1.5 mutants derived from SARS-CoV-2 Omicron BA.2 are spreading rapidly across the United States. Studies have shown that bivalent mRNA boosters provide additional protection against symptomatic XBB/XBB.1.5 infection during at least the first 3 months in recipients of two to four monovalent vaccines. However, the studies did not provide VE estimates for bivalent COVID-19 vaccines based on mRNA technology. Notably, the bivalent enhancers contain mRNA encoding the spike (S) gene of two SARS-CoV-2 strains, the ancestral strain and the Omicron sublines BA.4/BA.5.

about studying

In the current study, the researchers recruited individuals who received SARS-CoV-2 testing at ICATT sites between December 1, 2022, and January 13, 2023, with suspicion of one or more COVID-19 and similar diseases. They provided comprehensive information on vaccination history, current symptoms, previous SARS-CoV-2 test results, and pre-existing health conditions, if any.

The authors used S-gene amplification failure (SGTF) in real-time reverse transcription-polymerase chain reaction (RT-PCR) as a proxy indicator of infection with BA.5-associated sublines (eg, BQ.1.1, BQ.1, BF.7). ) and the presence of the S gene target (SGTP) as an indicator of XBB infection, including infection by BN.1, and other BA.2 substrains.

They report the quantitative results as cycle threshold (CT) values ​​for three SARS-CoV-2 genes, S, nucleocapsid (N), and open reading frame (ORF1ab). CTs of the S gene larger than four cycles above average N and ORF1ab indicated SGTF, thus SARS-CoV-2-positive samples with no SGTF are considered SGTP.

The team also calculated bivalent supportive relative VE and odds ratios (ORs) using multivariate logistic regression models. For VE calculations based on SGTF/SGTP status, they used the formula (1 – OR) x 100.

Results

By the end of the first week of December 2022, 13% of samples sequenced at ICATT sites belonged to Omicron BA.2 sublines, with XBB.1.5 and XBB mutations contributing to 2.4% and 5% of cases, respectively.

By the end of the study period, the number of cases had increased to approximately 41%, with 37.2% and 4% of cases due to XBB.1.5 and XBB, respectively. By 16 January 2023, the prevalence of XBB.1.5 had continuously increased nationwide, as assessed by whole genome sequencing (WGS), although WGS results for all samples collected during the study period were not available.

Among the results of 29175 nucleic acid Amplification Tests (NAATs), 10,596 (78%) and 3,052 (22%) were SGTF and SGTP, respectively. Between December 1, 2022, and January 2, 2023, XBB.1.5 made up 33% of the samples that exhibited SGTP, with XBB.1.5 accounting for 38% of them, and this increased to 43% between December 18, 2022, and January 2, 2023.

The relative VE of a bivalent booster dose in individuals aged 18–49 years was 52% and 48% against symptomatic BA.5 and XBB/XBB.1.5 infection, respectively. Similarly, 43% and 37% among subjects aged 50–64 years and 65 years were against symptomatic BA.5 infection, respectively. However, VE remained similar against BA.5-related infections and XBB/XBB.1.5-related infections across age groups. All of these individuals had received booster shots two to three months prior, while the controls had not received a bivalent booster.

Interestingly, among the controls, more patients who tested positive for SARS-CoV-2 reported receiving a bivalent booster than those who tested positive. Also, only 45% of monovalent vaccine recipients reported a positive result for SARS-CoV-2 compared to bivalent dose recipients (45% vs 34%). The median time since the last dose among monovalent vaccine recipients was 13 months for both the case patients and the control group.

conclusions

XBB mutants, especially XBB.1.5, appear to gain dominance because they account for more than 50% of sample sequences in environmental studies evaluating VE. Accordingly, the study highlighted the need for continued VE monitoring amid the emergence of new variants of SARS-CoV-2, such as XBB.1.5, with additional mutations in the receptor-binding domain of S compared with XBB. It is currently unclear how this mutation might affect VE.

However, because bivalent vaccines confer additional protection against infections associated with BA.5 and XBB symptoms in previously vaccinated individuals, all subjects should receive a bivalent booster dose as soon as they become eligible.

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