Respiratory Diseases Roundup

The Latest in COVID-19 News: Vaccine Effectiveness, 4-in-1 Home Test, Metformin and Long COVID

Edited by:
Kate Young

Key Highlights

  • 2024-2025 COVID-19 vaccination was associated with 40% vaccine effectiveness (VE) against hospitalization and 79% VE against invasive mechanical ventilation or death among hospitalized adults.1
  • A newly marketed OTC 4-in-1 antigen home test can simultaneously detect RSV, influenza A, influenza B, and SARS-CoV-2 in people aged ≥6 months (adult-administered for young children).2
  • In a large retrospective cohort, initiating metformin within 90 days after COVID-19 diagnosis among adults with overweight or obesity was associated with lower 1-year risk of post–COVID-19 condition (HR, 0.36).4

2024-2025 COVID-19 Vaccine Effectiveness in Hospitals1

In a multicenter, test-negative, case-control study conducted at 26 US hospitals (September 1, 2024, to April 30, 2025), investigators estimated effectiveness of 2024-2025 COVID-19 vaccines against severe outcomes among adults hospitalized with COVID-19–like illness. Cases had positive SARS-CoV-2 nucleic acid or antigen tests; controls tested negative. Vaccine exposure was receipt of a 2024-2025 COVID-19 vaccine ≥7 days before illness onset, and models adjusted for demographics, clinical characteristics, and region.

Among 8493 participants (1888 cases; 6605 controls; median age, 66 years), estimated vaccine effectiveness (VE) against COVID-19–associated hospitalization was 40% (95% CI, 27%-51%), with protection described as sustained through 90 to 179 days after vaccination. VE against the most severe in-hospital outcome—invasive mechanical ventilation or death—was 79% (95% CI, 55%-92%). Using whole-genome sequencing in approximately half of cases, the study also reported lineage- and mutation-stratified VE estimates across multiple JN.1 descendant lineages circulating during the season (including KP.3.1.1, XEC, and LP.8.1), with some estimates noted as imprecise when sample sizes were small.

FDA-Cleared 4-in-1 Home Antigen Test for RSV and Flu2,3

In a recent press release, ACON Laboratories announced retail availability of the Flowflex Plus RSV + Flu A/B + COVID 4-in-1 test, described as the first FDA-cleared home test intended to detect 4 respiratory infections—respiratory syncytial virus (RSV), influenza A, influenza B, and SARS-CoV-2—using a single over-the-counter rapid antigen assay. The company announcement states the test is cleared for adults and children as young as 6 months, when administered by an adult, and highlights use of a proprietary nasal swab guard for younger pediatric use.

The release describes the test as intended to help users distinguish among respiratory pathogens with overlapping symptom profiles (eg, fever, cough, congestion). It notes the assay “simultaneously detects” RSV, influenza A, influenza B, and COVID-19, positioning it for at-home decision-making about next steps such as contacting a clinician, limiting exposures, or seeking confirmatory testing, depending on local practice and patient risk. As with other over the counter antigen assays, clinical use considerations include timing relative to symptom onset, the potential need for repeat or confirmatory testing when suspicion remains high, and ensuring age-appropriate specimen collection and interpretation by caregivers for infants and young children, according to the CDC.3

Metformin and Post–COVID-19 Condition Risk4

A population-based retrospective cohort study evaluated whether starting metformin after SARS-CoV-2 infection was associated with a lower risk of post–COVID-19 condition (PCC) among individuals with overweight or obesity. In the reported analysis population of 624,308 patients, 2976 initiated metformin within 90 days of COVID-19 diagnosis.

In an intention-to-treat analysis, the 1-year risk difference for PCC associated with metformin initiation was −12.58%, with a hazard ratio of 0.36 (95% CI, 0.32-0.41); results were described as consistent across subgroup analyses. The authors noted a key limitation: findings may not apply to individuals with a normal body mass index. The publication’s conclusion states that early metformin treatment in people with overweight or obesity “may reduce” PCC risk, and calls for further research to confirm causality and clarify metformin’s role in PCC management.

References:

  1. Ma KC, Webber A, Lauring AS, et al. Estimated effectiveness of 2024-2025 COVID-19 vaccination against severe COVID-19. JAMA Netw Open. 2026;9(2):e2557415. Published 2026 Feb 2. doi:10.1001/jamanetworkopen.2025.57415
  2. Flowflex launches first FDA-cleared 4-in-1 home test detecting RSV, flu A/B and COVID for Ages 6 Months+. https://www.prnewswire.com/news-releases/flowflex-launches-first-fda-cleared-4-in-1-home-test-detecting-rsv-flu-ab-and-covid-for-ages-6-months-302668750.html. Published January 23, 2026. Accesed March 9, 2026.
  3. Centers for Disease Control and Prevention. Overview of Testing for SARS-CoV-2 (COVID-19). Updated September 28, 2022. Accessed March 10, 2026. https://www.cdc.gov/covid/hcp/clinical-care/overview-testing-sars-cov-2.html
  4. Chaichana U, Man KKC, Ju C, Makaronidis J, Wei L. Effect of metformin on the risk of post-coronavirus disease 2019 condition among individuals with overweight or obese: a population-based retrospective cohort study. Clin Infect Dis. Published online September 1, 2025. doi:10.1093/cid/ciaf429