Children and adolescents: Respiratory infection and long-term effects longitudinal study (CARE Study): Study protocol

Mark McMillan; Rebecca Beazley; Nan Vasilunas; Thomas R Sullivan; Tess Edmond; Ailish Battersby; Philip N Britton; Brendan McMullan; Jon Jureidini; Sarah Del Fante; Helen S Marshall

doi:10.1371/journal.pone.0341566

Children and adolescents: Respiratory infection and long-term effects longitudinal study (CARE Study): Study protocol

PLoS One. 2026 Feb 5;21(2):e0341566. doi: 10.1371/journal.pone.0341566. eCollection 2026.

Authors

Mark McMillan^{1

2}, Rebecca Beazley³, Nan Vasilunas⁴, Thomas R Sullivan^{5

6}, Tess Edmond⁷, Ailish Battersby⁷, Philip N Britton^{8

9}, Brendan McMullan^{10

11}, Jon Jureidini¹², Sarah Del Fante³, Helen S Marshall^{1

2}

Affiliations

¹ University Department of Paediatrics, Women's and Children's Hospital Network, North Adelaide, South Australia, Australia.
² Adelaide Medical School and Robinson Research Institute, University of Adelaide, North Adelaide, South Australia, Australia.
³ Communicable Disease Control Branch, South Australia Health, Adelaide, South Australia, Australia.
⁴ Infectious Disease Department, Women's and Children's Hospital Network, North Adelaide, South Australia, Australia.
⁵ Women and Kids Theme, South Australian Health and Medical Research Institute, Adelaide, South Australia, Australia.
⁶ School of Public Health, The University of Adelaide, Adelaide, South Australia, Australia.
⁷ Department of General Medicine, Women's and Children's Hospital Network, North Adelaide, South Australia, Australia.
⁸ Department of Infectious Diseases and Microbiology & Child and Adolescent Health, Children's Hospital Westmead, Westmead, Australia.
⁹ Sydney Medical School, University of Sydney, Camperdown, New South Wales, Australia.
¹⁰ Department of Infectious Diseases, Sydney Children's Hospital, Randwick, New South Wales, Australia.
¹¹ School of Clinical Medicine, Faculty of Medicine and Health, University of New South Wales, Kensington, New South Wales, Australia.
¹² Critical and Ethical Mental Health (CEMH), Robinson Research Institute, University of Adelaide, Adelaide, South Australia, Australia.

Abstract

Background: The effects of SARS-Cov-2 infection can extend beyond the acute phase of the illness, often described as Long COVID, post-COVID condition (PCC) or Post-acute sequelae of COVID (PASC). Post-acute sequelae (PAS) are also likely to be a problem for a small proportion of children and adolescents following influenza infection. However, there is no comprehensive ongoing data collection in Australian children and adolescents, and global data on both PCC during the SARS-Cov-2 Omicron variant period and PAS following influenza is limited.

Aim: This study aims to determine the cumulative incidence of PCC in Australian children and adolescents five years after the start of the COVID-19 pandemic. Secondary aims include identifying the cumulative incidence of PAS in children and adolescents following influenza infection.

Methods: This longitudinal cohort study will recruit children and adolescents aged 0-18 years in South Australia who tested positive for SARS-Cov-2 or influenza in the previous 2 months. Following consent, participants will complete an online baseline survey and then at 3, 6, and 12 months post-infection. The survey has been adapted from the International Severe Acute Respiratory and Emerging Infection Consortium (ISARIC) Paediatric COVID-19 follow-up survey. The survey includes validated assessment tools such as the Pediatric Quality of Life Inventory (PedsQL), Multidimensional Fatigue Scale, and the Malmö Postural Orthostatic Tachycardia Syndrome (POTS) Score questionnaire. PCC following COVID-19 and PAS following influenza infection will be identified according to an adapted World Health Organization definition of PCC in children and adolescents.

Discussion: This study addresses gaps in understanding PCC and PAS following influenza in children and adolescents during Omicron circulation. Whilst it is no longer feasible to prospectively compare post-acute sequelae in children and adolescents who have never had COVID-19, this design allows a comparison with another common viral infection, influenza, informing clinical management of children post-infection.

Copyright: © 2026 McMillan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

MeSH terms

Adolescent
Australia / epidemiology
COVID-19* / complications
COVID-19* / epidemiology
COVID-19* / virology
Child
Child, Preschool
Female
Humans
Incidence
Infant
Infant, Newborn
Influenza, Human* / complications
Influenza, Human* / epidemiology
Longitudinal Studies
Male
Post-Acute COVID-19 Syndrome
Respiratory Tract Infections* / epidemiology
SARS-CoV-2 / isolation & purification