key: cord-0847046-fh9e37tp
authors: Seki, Masafumi
title: Lessons from the Nationwide Surveillance of SARS-CoV-2 Surges in Japan
date: 2021-07-06
journal: JMA J
DOI: 10.31662/jmaj.2021-0091
sha: b5c665a1731c8e8461859b0afb57cb889914382d
doc_id: 847046
cord_uid: fh9e37tp

nan

conditions (1) . Hence, age remains one of the most important factors to determine the prognosis of patients infected with SARS-CoV-2. Therefore, COVID-19 can be considered a formidable infectious disease with two distinct manifestations.

These two serious characteristics of SARS-CoV-2-infectivity and lethality-have been confirmed epidemiologically through an analysis of nationwide surveillance data during the first to the third wave of COVID-19 in Japan (5) .

The authors of that study demonstrated that the first wave in spring 2020 was characterized by the detection of infected patients from China followed by a notification of sporadic cases, including the "Diamond Princess" cruise ship and music clubs in Osaka (3) , (4) . Seemingly healthy people could spread SARS-CoV-2 during intensive activities in enclosed environments. It has been clear that infected asymptomatic individuals can transmit the virus as soon as 2 days after infection (5) .

The second wave in summer 2020 showed a large increase in notifications and a younger age distribution. Testing, especially polymerase chain reaction tests, became more available in the summer compared with that in the spring, and the test positivity declined. Moreover, it was found that the younger population was experiencing substantially milder cases of the disease. Although the mortality associated with COVID-19 remained low, severe and fatal cases skewed toward the aged, particularly older men. The data suggested that the mortality remained lower even when including the number of deaths at 1 month after the end of each wave to account for any "time lag (5) ."

The third wave in winter 2020 was characterized by steady notifications and a relatively high prevalence of hospitalized cases, and resulted in substantially higher mortality and morbidity, surpassing both the total and fatal case counts from the first two waves combined. Although the magnitude of the increases in mortality and morbidity varied, a surge was observed in urban and rural areas nationwide. To stimulate the economy, "Go Out To Eat" and "Go Travel" campaigns were introduced by the Japanese government to encourage dining out and taking domestic trips, respectively, which might have affected and exacerbated the COVID-19 pandemic (5) .

In all three COVOD-19 waves in Japan, the characteristic infectivity and lethality of SARS-CoV-2 was observed, but the propagation of the disease and its mortality varied depending on the situation and the backgrounds of the patients. The importance of molecular epidemiology has become increasingly apparent. If we continue to carry out appropriate nationwide surveillance, we should be able to predict and prepare for the next wave. Although we are already in the midst of a fourth wave, which is larger than the previous three, and numerous mutations of the virus with varying degrees of infectivity and lethality have already been observed, we can overcome this crisis by the rapid and widespread distribution of novel COV-ID-19 vaccines and continued interventions such as universal masking and hand washing.

Clinical characteristics of 138 hospitalized patients with 2019 novel Coronavirus-infected pneumonia in Wuhan, China

Initial genetic characterization of the 1918

Cluster of severe acute respiratory syndrome Coronavirus 2 infections linked to music clubs in Osaka

Environmental sampling for severe acute respiratory syndrome Coronavirus 2 during a COVID-19 outbreak on the Diamond Princess Cruise Ship

Epidemiology of coronavirus disease 2019 in Japan: descriptive findings and lessons learned through surveillance during the first three waves

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