Augie RayHow to misinterpret research:
A study finds that severe #COVID19 cases have a much higher risk of severe post-acute sequelae compared to flu. However, post-acute outcomes "occur with similar frequency among non-severe COVID-19 cases and influenza cases."
That last part encouraged some to say COVID and flu were similar. Wrong:
1) Severe acute COVID has much worse outcomes, and
2) People get the flu once every 5 to 10 years but COVID every 18 to 24 months.
https://www.medrxiv.org/content/10.1101/2025.05.30.25328674v1
Long-term risk of post-acute sequelae among adults following SARS-CoV-2 or influenza virus infection: a retrospective cohort study in a large, integrated healthcare system
Background: The comparative risk of post-acute sequelae (PAS) associated with SARS-CoV-2 and influenza virus infection remains unclear. Methods: We undertook a retrospective cohort study within the Kaiser Permanente Southern California healthcare system of COVID-19 and influenza cases who received acute respiratory illness (ARI) diagnoses in virtual, outpatient, or inpatient settings between 1 September, 2022 and 31 December, 2023. We monitored PAS-associated healthcare utilization across all settings through 180 days after index ARI diagnoses. We estimated adjusted hazard ratios (aHRs) comparing COVID-19 cases to influenza cases, weighting to account for cases' probability of retention in follow-up and infection with SARS-CoV-2 or influenza virus at the index ARI episode. Results: Analyses included 74,738 COVID-19 cases and 18,790 influenza cases, among whom 35,835 (38.3%), 26,579 (28.4%), 23,388 (25.0%), and 7,726 (8.3%) received care for their index ARI episodes in virtual, ambulatory, emergency department, and inpatient settings, respectively. Risk of PAS diagnoses in any clinical setting was similar among COVID-19 and influenza cases (aHR=1.04 [95% confidence interval: 0.99-1.09] and aHR=1.01 [0.97-1.06] 31-90 and 91-180 days after index, respectively). However, COVID-19 cases experienced higher risk of severe PAS conditions necessitating inpatient care (aHR=1.31 [1.07-1.59] and aHR=1.24 [1.03-1.49] 31-90 and 91-180 days after index, respectively). This heightened risk of severe PAS following COVID-19 was concentrated among patients who required inpatient admission at their index episode. Conclusions: PAS outcomes occur with similar frequency among non-severe COVID-19 cases and influenza cases. However, PAS among COVID-19 cases are more likely to require hospital admission than PAS among influenza cases. ### Competing Interest Statement JAL has received honoraria from Pfizer, Inc.; Merck, Sharp & Dohme; Vaxcyte, Inc.; Valneva, SE; and Seqirus, Inc., all unrelated to the submitted work. SYT has received grant funding from Pfizer, Inc. unrelated to the submitted work. ### Funding Statement This work was supported by the US Centers for Disease Control and Prevention (grant 75D30123-C-18129 to SYT). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was reviewed and approved by the Kaiser Permanente Southern California Institutional Review Board with a waiver of informed consent and was conducted consistent with federal law and CDC policy (45 C.F.R. part 46.101(c); 21 C.F.R. part 56). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The raw data used in this manuscript include protected health information (e.g. dates of diagnoses and testing) that cannot be shared openly without appropriate human subjects approval and data use agreements. Kaiser Permanente Southern California (KPSC) institutional policy requires a data transfer agreement to be executed between KPSC and the individual recipient entity prior to transmittal of patient-level data outside KPSC. Requests for data can be addressed to the Central Business Office of the Department of Research and Evaluation (contact via Diane.C.Robinson{at}kp.org).
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