Mid-Pandemic RSV and HPIV-3 Patterns in Young Children and Their Families

In children aged 0 to 4 years, rates of symptomatic respiratory syncytial virus (RSV) and human parainfluenza virus type 3 (HPIV-3) were 4-fold higher than rates of COVID-19 infection between November 2020 and March 2021, according to study findings recently published in Clinical Infectious Diseases.

Prior to the COVID-19 pandemic, most children had been infected by RSV and HPIV-3 by the age of 2 years. However, changing behavior patterns during the pandemic appeared to suppress these illnesses in the US until the spring of 2021, when substantial nationwide increases in these infections lead to a CDC alert regarding RSV. Researchers therefore sought to characterize the burden of HPIV-3 and RSV in children aged 0-4 years and infection patterns in their households in the middle of the COVID-19 pandemic — between November 2020 and March 2021 — using data from the SEARCh longitudinal household cohort surveillance study, which was originally undertaken to examine SARS-CoV-2 epidemiology in Maryland households with children.

The SEARCh cohort used in the current analysis included 175 households comprising 690 individuals, including 256 children 0 to 4 years of age (38 of whom were less than 1 year of age), 100 children 5 to 17 years of age, and 334 adults 18 to 74 years of age. All participants had weekly nasal swabs collected for SARS-CoV-2 molecular testing, with additional nasal swabs obtained at the onset of any “COVID-19-like illness” (CLI) — defined as “fever, cough, shortness of breath, chills, nasal congestion, sore throat, chest pain, and fussiness.” Adult participants completed weekly questionnaires regarding activities outside their home, including in-person attendance at school, work, and child care. Those reporting CLIs were asked whether medical attention had been sought or whether hospitalization was required.

Demographically, 87% of the participants were White, 6% were multiracial, 4% were Black, 2% were Asian, and 1% were “other race,” with 95% of the participants reporting that they were non-Hispanic. At study enrollment, 49% of the children 0 to 4 years of age attended child care outside the home, 23% of the children 5 to 17 years of age attended in-person school, and 42% of the adults worked outside the home.

CLIs were reported in 194 children from 142 households during the study period. A total of 392 CLI episodes were reported, with 781 nasal swabs available for testing by multiplex PCR. To establish the duration of infection, 167 additional specimens from children aged 0 to 4 years with at least 1 HPIV-3-positive nasal swab and 116 nasal swabs from those with at least 1 RSV-positive nasal swab were tested via singleplex PCR for the respective pathogen. Researchers also tested nasal swabs of household members of those with HPIV-3 or RSV infection with singleplex PCR for the duration of the time the illness was present in the household.

Incidence rates (IRs) of symptomatic infection for each virus were compared among children aged 0 to 4 years during epidemic periods (ie, the intervals between the first and last infections with each virus in the cohort). The epidemic period for HPIV-3 was April 18, 2021, to August 22, 2021 and for RSV was May 30, 2021, to October 3, 2021, with SARS-CoV-2 divided into 2 epidemic periods of November 29, 2020, to February 27, 2021, and February 28, 2021 to May 29, 2021. Notably, while the epidemic period of HPIV-3 infection was consistent with the US pre-pandemic seasonal pattern for HPIV-3 infection, the epidemic period for RSV — from June through the end of the study in October — was well outside the typical pre-pandemic RSV season of November through March. The study’s RSV epidemic period findings were also consistent with “the unusual surge in RSV cases in the summer and fall of 2021 detected by national surveillance,” study authors noted.

Individuals with HPIV-3 (n=45) or RSV (n=46) infections were found in 23.4% (41 of 175) of the households evaluated. Among children aged 0 and 4 years, IRs of symptomatic infection per 1000 person-weeks were as follows: (1) 8.7 for HPIV-3 (95% CI, 6.0-12.2); (2) 7.6 for RSV (95% CI, 4.8-11.4); and (3) 1.9 for SARS-CoV-2 (95% CI, 1.0-3.5).

Researchers also examined factors related to the primary household infection, which was defined as the earliest infection detected. Of the 36 primary HPIV-3 or RSV infections reported, all but 1 were in children aged 0 to 4 years. Children in child care or those who attended preschool had a higher likelihood of primary infection (odds ratio, 10.81; 95% CI, 3.14-37.23).

Several study limitations warrant mention. Individuals who self-identified as non-White or non-Hispanic, as well as those with a low income, were underrepresented in the SEARCh cohort, which may limit the generalizability of the findings. Further, the investigators focused their analysis on children 0 to 4 years of age with CLIs and their household members because multiplex PCR testing resource constraints prevented the assessment of all nasal swabs.

The authors concluded that in the cohort of children aged 0 to 4 years, “IRs of symptomatic HPIV-3 and RSV infection were four-fold higher than for SARS-CoV-2 during epidemic periods,” and that “HPIV-3 and RSV were almost exclusively introduced into the households by infants and preschool children.” The researchers added that “This study and others highlight the continued importance of HPIV-3 and RSV as pediatric pathogens in the COVID-19 pandemic era and underscore the importance of HPIV-3 vaccine and RSV vaccine and monoclonal antibody development and implementation.”

Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.