The incidence of acute respiratory illnesses (ARIs) decreased during the COVID-19 pandemic, corresponding with widespread use of public health measures aimed at reducing transmission of SARS-CoV-2, according to a study in Influenza and Other Respiratory Viruses.
Investigators assessed changes in the circulation of respiratory viruses during multiple early waves of the pandemic, examining data from the Household Influenza Vaccine Evaluation (HIVE) cohort. The longitudinal HIVE cohort includes 300 to 400 households per year in southeastern Michigan who have participated in active ARI surveillance since 2011. Data included in the current analysis are from March 1, 2020, to June 30, 2021.
All participants included for analysis had blood draws from 3 sero-surveillance periods: summer 2020, fall-winter 2020, and spring 2021. Serum specimens were assessed with electrochemiluminescence immunoassay to measure antibody levels against SARS-CoV-2 spike protein, SARS-CoV-2 spike protein receptor-binding domain, and SARS-CoV-2 nucleocapsid (N) protein. Adult cohort members were also surveyed from July to August 2020 and May to July 2021 on COVID-19 mitigation practices. Incidence rates (IR) of ARI and virus detection were calculated per 100 person-years for the study period and for a pre-pandemic period (March 1, 2016, to June 30, 2017).
The current analysis involved 437 individuals reporting 772 ARI episodes between March 1, 2020, and June 30, 2021, with 162 individuals reporting 1 or more ARI episodes (range, 1-11). The incidence rate (IR) for ARI during this period of the pandemic was 39.4 (95% CI, 36.7-42.3) per 100 person-years; in contrast, during a similar-length period prior to the pandemic (March 1, 2016, to June 30, 2017), the ARI incidence rate was 76.9 (95% CI, 72.4-81.6) per 100 person-years. Thus, the incidence rate ratio (IRR) for the pandemic period to pre-pandemic period incidence rates was 0.5 (95% CI, 0.5-0.6; P <.001).
Of the 626 specimens from ARI symptom onset, 343 tested positive for 1 or more respiratory virus. The IRR of the incidence of test-positive ARI specimens during the pandemic period to the incidence during the pre-pandemic period was 0.3 (95% CI, 0.3, 0.4; P <.001).
Rhinovirus (RV) was detected in each month of the study period and was the most common virus detected, with 43.6% of all specimens positive for RV. The IRR for the RV incidence during the study period to the RV incidence during the pre-pandemic period was 0.5 (95% CI, 0.5- 0.6; P <.001).
Seasonal coronavirus NL63 had the next-highest detection frequency, with 4.2% of all specimens testing positive. Influenza was detected in 7 ARI specimens (2.0% of positive tests), and SARS-CoV-2 was detected in 13 (3.8%).
Among 326 adults who participated in the first survey, 89.8% reported always wearing a face mask or cloth covering when in public. Of 390 participants who completed the second survey, 52.8% reported always wearing a face mask or cloth covering when in public. The investigators observed an increase in ARI reports and infections when reduced adherence to mitigation practices was reported.
A total of 29 (7.1%) specimens were seropositive for antibodies against the SARS-CoV-2 N protein, which indicates previous SARS-CoV-2 infection. The study authors observed 14 (5.3% of 265) cases during summer 2020, 8 (3.0% of 269) during fall/winter 2020, and 7 (11.3% of 62) in spring 2021.
With regard to study limitations, the researchers noted that respiratory virus infections may have been undetected by study assays if the participants had viral loads below detectable limits at the time of collection. Also, ARI episodes were mild and may not be representative of more severe illness, and generalizability to other populations is limited.
“The burden of ARI in the HIVE cohort during the COVID-19 pandemic fluctuated, with declines occurring concurrently with the widespread use of public health measures,” study authors concluded. “Rhinovirus and seasonal coronaviruses continued to circulate even when influenza and SARS-CoV-2 circulation was low.
Disclosure: One of the study authors declared an affiliation with a pharmaceutical company. Please see the original reference for a full list of authors’ disclosures.
Fine SR, Bazzi LA, Callear AP, et al. Respiratory virus circulation during the first year of the COVID-19 pandemic in the Household Influenza Vaccine Evaluation (HIVE) cohort. Influenza Other Respir Viruses. 2023;17(3):e13106. doi:10.1111/irv.13106