key: cord-0861208-b003vcdc
authors: Wiese, Andrew D; Everson, Jordan; Grijalva, Carlos G
title: Social distancing measures: evidence of interruption of seasonal influenza activity and early lessons of the SARS-CoV-2 pandemic
date: 2020-06-20
journal: Clin Infect Dis
DOI: 10.1093/cid/ciaa834
sha: 7cf5b14c782612c68064949ccce3af851039fc0b
doc_id: 861208
cord_uid: b003vcdc

nan

M a n u s c r i p t

The unprecedented enactment of social distancing measures in response to the SARS-CoV-2 pandemic -including city lockdowns, school closures, stay-at-home orders, case isolation, quarantine of contacts, etc.was aimed at reducing the transmission of the virus and its burden on healthcare systems. Since influenza and other common respiratory pathogens share a similar mode of transmission with SARS-CoV-2, their transmission could be indirectly impacted by those measures. And while novel surveillance systems have been implemented to monitor SARS-CoV-2 activity, pre-existing surveillance systems have the advantage of allowing comparison to trends in prior years to assess the impact of social distancing measures on the activity of influenza and other respiratory pathogens.

Syndromic surveillance is an important public health tool for the early detection, monitoring and characterization of outbreaks, and supports targeted investigations that may include detailed clinical and laboratory assessments. Syndromic surveillance is especially informative when diagnostic tests are not available, applied selectively, or difficult to implement on a broad scale. Globally, syndromic surveillance systems of influenza-like illness (ILI) are maintained to characterize the onset, circulation, and characteristics of influenza activity. These activities are typically complemented with surveillance of laboratory-confirmed detection of influenza infections. Maintained over multiple years, these surveillance systems help identify syndromic and viral activity that deviates from previous years' patterns.

In this issue of the journal, Hyunju Lee and colleagues describe the use of national influenza surveillance data to assess the impact of social distancing measures, implemented in response to the SARS-CoV-2 pandemic, on seasonal influenza activity in Korea. Previous reports have demonstrated that the implementation of social distancing measures was associated with reductions in SARS-CoV-2 infections. [1] [2] [3] In this study, investigators compared the A c c e p t e d M a n u s c r i p t While surveillance data are helpful to identify abnormal activity of certain diseases of public health interest, and to demonstrate the impact of major interventions, such as implementation of social distancing measures, it is important to understand the limitations and strengths of specific surveillance systems. Monitoring a new disease that rapidly reaches pandemic proportion is difficult for surveillance systems that rely on patients presenting to healthcare settings and getting tested. Due to fear or other reasons, patients may avoid or delay healthcare encounters unless strictly necessary, and changes in testing practices could also affect the data captured by surveillance systems. Complementing laboratory-based surveillance with syndromic surveillance data is helpful, but additional research is necessary to clarify and characterize the general healthcare utilization patterns during the pandemic.

In Korea, the US and most other settings, several social distancing measures were implemented in rapid sequence, making it difficult to isolate the impact of specific measures due to their temporal and regional aggregation. Although the described comparisons are ecologic in nature, the population level assessment of the impact of these broad recommendations may be more relevant than individual level evaluations. Finally, it is important to understand that there may be substantive surveillance variation over time and across regions ( Figure) , and thus national figures may not represent the local or regional situation.

Looking beyond influenza, these surveillance systems will be important in different regions and countries as they initiate or continue relaxing social distancing requirements. In the US, a two-week downward trend in ILI and CLI activity was recommended as one indicator for reopening. 10 Despite declines following social distancing, CLI activity levels remained substantially elevated in certain regions through mid-May 2020, suggesting that high activity levels could rapidly resume once distancing measures are removed. In contrast with the abrupt 

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