key: cord-353608-de6rrf7v
authors: Saito, Sho; Asai, Yusuke; Matsunaga, Nobuaki; Hayakawa, Kayoko; Terada, Mari; Ohtsu, Hiroshi; Tsuzuki, Shinya; Ohmagari, Norio
title: First and second COVID-19 waves in Japan: A comparison of disease severity and characteristics: Comparison of the two COVID-19 waves in Japan
date: 2020-11-02
journal: J Infect
DOI: 10.1016/j.jinf.2020.10.033
sha: 
doc_id: 353608
cord_uid: de6rrf7v

• Coronavirus disease has emerged as a global pandemic. • Japan has experienced two waves of the disease. • The second wave had a lower proportion of severe cases on admission.

has become a global pandemic, occurring in forming several peaks in waves 2, 3 . This study compared the severity and characteristics of the first and second waves in Japan.

We obtained the study data from the COVID-19 Registry Japan (COVIREGI-JP). The COVIREGI-JP includes data from a observational cohort study using medical records in Japan. The criteria for enrolment were (1) tests such as polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP) that turned positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and (2) inpatient treatment at a health care facility. We evaluated age, sex, comorbidities, disease severity at admission, supportive care, medications, and the outcome on discharge. A patient's condition was denoted as "severe" on fulfilment of one or more of the following criteria: the need for invasive or non-invasive mechanical ventilation, need for supplemental oxygen, an oxygen saturation (SpO 2 ) of < 94% at room air, and tachypnoea (respiratory rate of >24 breaths per minute). Patients who did not meet these criteria were classified as "non-severe" at admission. Patients admitted between 26 January and 31 May 2020, were included in the first wave, and those admitted between 1 June and 31 July 2020, were included in the second wave 4 (frozen data as of 2 September 2020). Continuous variables were expressed as medians and interquartile ranges, and categorical variables were expressed as numbers (%). All statistical analyses were conducted using R version 4.0.2 (R core Team).

Data of 5194 cases from 327 facilities were included in the analysis: 3833 and 1361 cases from the first and second waves, respectively. At admission, the second wave had a smaller proportion of severe cases (12.0% vs 33.1%, Fig. 1a ); the duration from onset to admission was also shorter (median, 4 vs 7 days) than that in patients in the first wave (Fig. 1b, 1c) . Patients in the second wave tended to be younger (median age, 37 vs 56 years), were less frequently transferred from other hospitals (3.8% vs 15.0%) and were less likely to have comorbidities such as cardiovascular diseases (1.9% vs 5.9%), and cerebrovascular disease (1.8% vs 6.1%). Mortality (1.2% vs 7.3%) in hospitalized or discharged patients was also lower in the second wave; the same trend was observed on stratification according to age and severity at admission (Table 1 ).

Our study showed that the proportion of cases involving severe disease at admission was smaller in the second wave. Considering the lower percentage of patients transferred from other hospitals in the second wave, it is likely that the first wave had a more critical effect on the ability of healthcare institutions to receive patients. Moreover, the number of PCR tests performed was greater in the second wave than in the first wave 5 . Earlier admission of patients in the second wave may reflect the increase in the number of PCR tests performed and the number of beds available to COVID-19 patients. Data from the second wave indicated a demographic shift toward a younger population with fewer comorbidities, a lower proportion of severe patients at admission, and decreased mortality.

However, the mortality was lower in second wave even if stratifying age and severity at admission.

This may be because of the shorter time between disease onset and admission, differences in patient background, comorbidities, and advances in treatment methods.

Although this registry gathers information on a large number of patients, it does not cover all patients in Japan, and data from the second half of the second wave was not included in this study; this may be a source of bias in this study. In addition, since data are updated daily, there is a possibility that future findings will differ from the current results.

The findings of our study indicated that in the first wave, the medical system was under greater strain with more severe cases on admission. In the second wave, patients were younger with fewer underlying diseases and lower mortality rates.

Declarations of interest: none.

This study was funded by Health and Labour Sciences Research Grant, "Research for risk assessment and implementation of crisis management functions for emerging and re-emerging infectious diseases (19HA1003)" e Immunosuppression includes neutropenia (< 500 neutrophils/μL), use of glucocorticoids/steroids within 1 month (doses greater or equal to an equivalent of 20 mg of prednisone per day for at least 1 month), chemotherapy or radiation therapy or the use of immunosuppressants (such as antitumor necrosis factor-α therapy, anti-IL-6 receptor/anti-CD20 monoclonal antibodies, selective T-cell co-stimulation blockers, methotrexate, tacrolimus) within the past 3 months, post hematopoietic stem cell transplantation, post organ transplantation, asplenia, and primary immunodeficiency syndrome or HIV infection.

f Patients who received these treatments at least once during their hospitalization were included. g Data were counted only for patients who were alive at discharge.

Abbreviations: COVID-19, coronavirus disease; ECMO, extracorporeal membrane oxygenation; IQR, interquartile range

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Characteristics and outcomes of COVID-19 patients during initial peak and resurgence in the Houston metropolitan area

Decreased case fatality rate of COVID-19 in the second wave: a study in 53 countries or regions

Labour and Welfare. The 6th advisory board for the control of COVID-19 Reference 3-1

We thank all the participating facilities for the provision of care to COVID-19 patients and for cooperation regarding data entry.
