Epidemic pattern of HFMD and the impact of COVID-19 intervention
From January 2019 to December 2022, a total of 2296 suspected HFMD cases were collected from sentinel hospitals for EV screening in Nanchang. Among the HFMD cases, 1321 (57.5%) were laboratory-confirmed (EV-positive) HFMD determined by real time RT-PCR. The pathogen spectrum of HFMD had a substantial change after the launch of EV-A71 vaccination in mid-2016, the typical biennial outbreak pattern gradually developed into less volatile mode as EV-A71-associated cases substantially decreased (Figure 2A, Supplementary Figure 1A). The monthly distribution of EV-positive cases during 2019-2022 were shown in Supplementary Figure 1B. CVA6 was the predominant agent accounting for 34.0-59.6% of EV-positive cases, followed by CVA16 (14.9-31.4%) and sporadic CVA10-associated cases, and the proportion of UEV reached to as high as 33.2% in 2019 (Supplementary Figure 2). To assess the potential impact of local COVID-19 outbreaks on EV transmission, a long time-span (2010-2022) etiology surveillance curve was displayed, and two predicted peaks was inserted to follow the epidemic pattern-biennial peak around May (Figure 2A). During the first local COVID-19 outbreak from January to March 2020, the HFMD incidence plunged and the expected epidemic peak vanished as result of a city-level lockdown along with the first-level PHER (Figure 2B). The prediction was supported by ARIMA forecasting in the absence of NPIs (Figure 2C-D). From then on, the dynamic Zero-Covid policy continued until the 3rd outbreak associated with Omicron variants in the end of 2022 (Figure 2B) (14). Apparently, the predicted peak of HFMD didn’t occur around May 2022 but a low-volatility plateau of HFMD incidence, which might be associated with the 2nd outbreak lasting for 2 months from March to May 2022.