The severity of Omicron BA.4/BA.5 lineages in the South Africa population

In a recent study posted to the Research Square* preprint server, researchers assessed the clinical severity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variants.

Study: Clinical severity of SARS-CoV-2 Omicron BA.4 and BA.5 lineages in South Africa. Image Credit: CROCOTHERY/Shutterstock
Study: Clinical severity of SARS-CoV-2 Omicron BA.4 and BA.5 lineages in South Africa. Image Credit: CROCOTHERY/Shutterstock

Background

The Network for Genomic Surveillance in South Africa (NGS-SA) detected the novel SARS-CoV-2 Omicron BA.4 lineage in January 2022 and BA.5 in February 2022. These lineages were responsible for the advent of the fifth wave of SARS-CoV-2 infections. Various studies have estimated that the BA.4 and BA.5 lineages multiply faster than BA.2. Moreover, compared to the BA.1 and BA.2 lineages, these BA.4 and BA.5 have been found to reduce serological neutralization in individuals vaccinated with three doses of the coronavirus disease 2019 (COVID-19) vaccines.   

About the study

In the present study, researchers evaluated the disease severity of infections caused by SARS-CoV-2 Omicron BA.4 and BA.5 lineages.

The team conducted a data linkage study wherein they obtained national individual-level information from the national COVID-19 case data, SARS-CoV-2 laboratory test data, and an active surveillance system called DATCOV that monitored data related to hospital admissions due to COVID-19 in South Africa. The dataset was limited to tests performed using the TaqPath™ COVID‑19 assay.

The team utilized a combination of the absence of the SARS-CoV-2 spike (S) gene, resulting in S-gene target failure (SGTF) or the presence of the S-gene resulting in S-gene target positive (SGTP) according to a set period according to circulating variants or lineages found via genomic surveillance. The SGTP COVID-19 infections observed between October and November 2021 were categorized as Delta infections, and those between February and April 2022 were categorized as BA.2 infections, while SGTF COVID-19 infections diagnosed between November and January 2022 were categorized as BA.1 infections, and those found in April 2022 were categorized as BA.4 or BA.5 infections. 

The team assessed risk factors for COVID-19-related hospitalization and severe disease among patients hospitalized due to COVID-19 comparing BA.4, BA.5, and Delta infections to BA.1 infections. The analysis was performed by controlling for factors related to hospitalization and severity.  

Results

The study results showed that a total of 884,379 COVID-19 cases were detected between 1 October 2021 and 26 April 2022. Among these, 16.3% were diagnosed via the TaqPath COVID-19 test. Furthermore, the team observed that based on the presence or absence of the S-gene, the SARS-CoV-2 Delta variant caused 1.3% of the infections, BA.1 caused 76.6%, BA.2 caused 20.3%, and BA.4 or BA.5 caused 1.8% of the infections.

Among adults aged 25 years and above, 76.2% of the total cases were Delta infections, 81.6% were BA.1, 66.5% were BA.2, and 78.7% were BA.4 or BA.5. Among children aged between five and 18 years, 24.7% of the total cases were BA.1 infections, 14.5% were Delta, 9.1% were BA.1, and 13.2% were BA.4 or BA.5.

Out of the COVID-19 patients who required hospitalization, 13.5% were diagnosed with Delta infections, 4.0% with BA.1, 3.3% with BA.2, and 4.8% with BA.4 or BA.5 infections. Furthermore, the number of reinfections detected was 9.7% for BA.1, 9.3% for BA.2, and 11.7% for BA.4 or BA.5 patients, compared to 2.9% for Delta patients.

Among the SARS-CoV-2-infected patients whose infecting variant or lineage was known, 3.9% were hospitalized. Moreover, among patients whose disease outcome was known, 33.4% developed severe COVID-19 infection, including 57.7% Delta, 33.7% BA.1, 26.2% BA.2, and 27.5% BA.4 or BA.5 patients.

Multivariable analysis showed that as compared to BA.1 infection, the odds of developing a severe disease were higher in Delta, lower in BA.2, and comparable in BA.4 or BA.5 infection. Furthermore, compared to patients between 19 and 24 years, individuals aged between 40 and 59 years and 60 years and above had higher odds of developing severe disease. Notably, the odds of developing a severe disease were lower in females and in individuals who had received one or more COVID-19 vaccine doses.

Overall, the study findings showed that patients infected with the SARS-CoV-2 Omicron BA.4 or BA.5 lineages had a comparable risk of developing severe disease and hospitalization to BA.1-infected patients. The researchers believe the present study could be useful in planning healthcare resources and developing vaccination policies.             

*Important notice

Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Bhavana Kunkalikar

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.

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