key: cord-0765758-kx6hehif
authors: Sunagawa, Satoko; Iha, Yoshikazu; Kinjo, Takeshi; Nakamura, Katsunori; Fujita, Jiro
title: Disappearance of summer influenza in the Okinawa prefecture during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic
date: 2020-11-16
journal: Respir Investig
DOI: 10.1016/j.resinv.2020.10.010
sha: b6e2e54b3152903659e9e2f0b642f611be76b8b8
doc_id: 765758
cord_uid: kx6hehif

Since the Okinawan islands are located in the southernmost part of Japan, where the climate is subtropical, several episodes of influenza epidemics occur during the summer season. More recently, we have demonstrated that summer influenza epidemics occur every year. After the outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) began in January 2020, measures to avoid disease transmission have been widely promoted in Japan, such as the use of masks, handwashing, remote work, and cancellation of large events. These measures might also have reduced the spread of other infectious diseases, such as the seasonal influenza. Based on this background, we evaluated weekly influenza activity in the 2019/2020 season. After the SARS-CoV-2 pandemic, the summer influenza in the Okinawa prefecture disappeared in 2020. The reasons for the disappearance of summer influenza in Okinawa are discussed herein.

In subtropical areas such as Taiwan, Hong Kong, and Singapore, influenza epidemics are observed throughout the year and influenza pandemics frequently occur in the summer season [1] . Since the Okinawan islands are located in the southernmost part of Japan (latitude 26°N), where the climate is also subtropical, several episodes of influenza epidemics occur during the summer season [2] [3] [4] [5] [6] [7] . It has been reported that summer influenza is one of the main causes of acute respiratory infections in children and adults in the summer season in the Okinawa prefecture [4] . In addition, in previous studies, we have demonstrated that influenza B viruses play an important role in summer epidemics [5, 6] .

Since the outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) began in January 2020, measures to avoid disease transmission have been widely promoted in Japan, such as the use of masks, handwashing, remote work, and cancellation of large events. If effective, these measures could also reduce the spread of other infectious diseases, such as seasonal influenza. Based on this background, we evaluated weekly influenza activity in the 2019/2020 season.

From September 2019 to September 2020, two individual influenza surveillance datasets were collected from external sources [6] . The first dataset included a nationwide surveillance of influenza diagnosed by rapid antigen test (RAT) results and/or influenza-like illness symptoms. The Japanese national influenza surveillance is In the present study, we clearly demonstrate that the summer influenza in the Okinawa prefecture disappeared in 2020. It has also been reported that seasonal influenza activity is lower in 2020 than in previous years in Japan [8] . In addition, it has been suggested that cases of the flu dropped in the Southern Hemisphere. From Chile to South Africa to New Zealand, countries reported far lower numbers of influenza cases.

Although influenza activity in the 2019/2020 season was moderately severe in other parts of the world [9] , influenza activity in our study may have been affected by temperature [5, 6, 10] However, as demonstrated in Figure 2 , although a significant number of RATs was performed in several hospitals, detection of influenza was extremely rare in the Okinawa prefecture. Therefore, the disappearance of summer influenza should not be attributed to the diminishment of RATs during the SARS-CoV-2 outbreak.

In conclusion, our study clearly demonstrated the disappearance of summer influenza in the Okinawa prefecture after the pandemic of SARS-CoV-2. 

Dynamic patterns of avian and human influenza in east and southeast Asia

changing patterns of seasonality and prevalence of amantadine-resistant influenza A virus

Epidemiology of influenza from 2007 to 2008 in the Naha area, Okinawa prefecture: surveillance of rapid antigen test results

Detection of various respiratory viruses in patients with influenza-like illness before and after emergence of the 2009 pandemic H1N1 influenza virus in Okinawa

Effect of climatic conditions on epidemic patterns of influenza in Okinawa, Japan, during the pandemic of 2009: surveillance of rapid antigen test results

Comparative epidemiology of influenza A and B viral infection in a subtropical region: a 7-year surveillance in Okinawa

An epidemiological analysis of summer influenza epidemics in Okinawa

Seasonal Influenza Activity During the J o u r n a l P r e -p r o o f SARS-CoV-2 Outbreak in Japan

Coronavirus Disease 2019 and Influenza 2019-2020

Global environmental drivers of influenza

We would like to thank Editage Inc. (www.editage.com) for English language editing. All authors are required to disclose any COI within 2 calendar years preceding the current year, prior to the submission of any manuscript in the subject matter of which any company, entity, or organization has an interest.

The authors have no conflicts of interest to declare.