Influenza A/B, RSV and SARS-CoV-2 Co-Detection Among Adults with Acute Respiratory Illness in Zimbabwe, 2022–2023: A Sub-Study of a COVID-19 Vaccine Effectiveness Study

Background/Objectives: Influenza, respiratory syncytial virus (RSV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cause overlapping respiratory illness, but Zimbabwean adult multipathogen data remain limited. We described influenza and RSV detection and co-detection with SARS-CoV-2 among adults enrolled in the ZIMCOVVAR study. Methods: This retrospective sub-study included nasopharyngeal specimens from adults with acute respiratory illness recruited in six Zimbabwean provinces during 2022-2023. Following exclusion of duplicate and unlinked records, 1,429 participants were analyzed. Influenza A, influenza B, and RSV were tested by multiplex real-time reverse-transcription polymerase chain reaction (PCR); recorded target cycle thresholds (Ct) ≤30 were provisionally classified as signals. Valid target-specific denominators remained unresolved. Proportions, confidence intervals, monthly patterns, and associations with SARS-CoV-2 status were examined. Results: The analytic cohort comprised 281 SARS-CoV-2-positive and 1,148 negative participants; median age was 35 years and 68.2% were female. Ct-defined influenza A, RSV, and influenza B signals occurred in 191/1,429 (13.4%), 53/1,429 (3.7%), and 2/1,429 (0.1%), respectively. Influenza A was recorded in 68/281 (24.2%) SARS-CoV-2-positive versus 123/1,148 (10.7%) negative participants. RSV was recorded in 3/281 (1.1%) versus 50/1,148 (4.4%), respectively. These are provisional signals per linked record, not valid-result positivity estimates; testing-group exclusion reversed the adjusted association. Conclusions: The selected adult cohort showed recorded influenza and RSV detections alongside SARS-CoV-2, supporting continued investigation of multiple respiratory pathogens in symptomatic adults. The findings require cautious interpretation because of nonrepresentative sampling and unresolved testing-group effects; quality-assured, multi-season surveillance is needed to inform local prevention planning.