mulTiplex Immunoassay qualiTy assuRance Panel

This is a single-visit study designed to collect serum samples from women who previously participated in the GBS6 clinical trial, "A placebo-controlled clinical trial investigating the safety and immunogenicity of GBS6 in pregnant women with and without human immunodeficiency virus (HIV) infection and their infants" (GBS6 trial). The purpose of this follow-up study is to obtain serum samples for the development of Quality Control Sera (QCS) and Assay Bridging (AB) panels to support long-term quality control and performance monitoring of the GASTON immunoassay.

The GBS6 trial enrolled 300 pregnant women between October 2022 and July 2023 at Kawempe National Referral Hospital and Kisenyi Health Centre IV. The last participant completed follow-up on 23 October 2024. Of these, 150 participants (75 living with HIV and 75 not living with HIV) were randomized to receive either the GBS6 vaccine or placebo (normal saline). The GBS6 vaccine is a capsular polysaccharide conjugate vaccine targeting the six most common disease-causing GBS serotypes.

For this follow-up study, only participants who received the GBS6 vaccine and are not living with HIV (n=75) will be contacted via telephone using the contact details provided in the GBS6 trial records. Each consenting participant will attend a single study visit for serum collection. Collected samples will be shipped to the City, St George's laboratory for antibody screening. The GASTON assay will measure IgG concentrations for serotypes Ia, Ib, II, III, IV, and V. Based on these results, samples will be ranked by IgG values, and an appropriate pooling strategy will be developed to generate the QCS and AB panels.

Inclusion criteria

• HIV-uninfected women who received the GBS6 vaccine during pregnancy and completed the whole period of study participation.
• Reachable by phone
• Willing and able to provide consent.
• Willingness to provide a blood sample.

Exclusion criteria

• Receipt of blood/plasma transfusion in the last 3 months
• Participants who receive treatment with immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids.
• Women who will test positive for Syphilis or HIV at screening
• Current alcohol abuse or illicit drug use, or with a psychiatric condition
• Major illness of the mother that, in the investigator's judgment, will substantially increase the risk associated with the participant's participation in the study, including but not limited to the following:

I. heart disease II. severe anaemia (Hemoglobin level less than 7.0g/dL)