Transmissibility quantification of norovirus outbreaks in 2016−2021 in Beijing, China

Abstract The transmissibility is a crucial feature for norovirus, yet its quantitative estimation has been limited. Our objective was to estimate the basic reproduction number ( R 0 ) of norovirus and investigate its variation characteristics. Norovirus outbreaks reported from September 2016 to August 2021 in Beijing were analyzed. The susceptible‐infected‐removed compartment model was established to estimate R 0 . Linear regression models and logistic regression models were used to explore the factors affecting the transmissibility of norovirus. The overall median R 0 of norovirus was estimated as 2.1 (interquartile range [IQR] 1.8–2.5), with 650 norovirus outbreaks. The transmissibility of norovirus varied by year, outbreak setting and genotype. The R 0 of norovirus during September 2019 to August 2020 (median 2.1, IQR 1.8–2.4) and September 2020 to August 2021 (median 2.0, IQR 1.7–2.3) was lower than that of September 2016 to August 2017 (median 2.3, IQR 1.8–2.7) ( β = 0.94, p = 0.05; β = 0.93, p = 0.008). The R 0 of norovirus for all other settings was lower than that for kindergarten (median 2.4, IQR 2.0–2.9) (primary school: median 2.0, IQR 1.7–2.4, β = 0.94, p = 0.001; secondary school: median 1.7, IQR 1.5–2.0, β = 0.87, p < 0.001; college: median 1.7, IQR 1.5–1.8, β = 0.89, p = 0.03; other closed settings: median 1.8, IQR 1.5–2.0, β = 0.90, p = 0.004). GⅡ.2[P16] outbreaks had a median R 0 of 2.2 (IQR 1.8–2.7), which was higher than that for GⅡ.6[P7] outbreaks (median 1.8, IQR: 1.8–2.0, odds ratio = 0.19, p = 0.03; GⅡ.2[P16] as reference) and mixed‐genotype outbreaks (median 1.7, IQR: 1.5–1.8, β = 0.92, p = 0.02; mixed‐genotype as reference). In kindergartens and primary schools, norovirus shows increased transmissibility, emphasizing the vulnerable population and high‐risk settings. Furthermore, the transmissibility of norovirus may change over time and with virus evolution, necessitating additional research to uncover the underlying mechanisms.