Introduction
Regarding COVID-19,
various situation has been observed in many countries [1]. Japan has presented
minus excess death in 2020, and held the Olympics on July 23, 2021 [2,3]. After
that, highest COVID-19 cases were found in Aug 20, the Paralympics was closed
on Sept 5 and cases were acutely decreased in October to November [4]. For
statistical data of COVID-19, John Hopkins University (JHU) have presented
current results every day [5]. The world infection situation is summarized [5].
COVID-19 has shown several strain mutations, and recent common type is Delta
strain. As to the new COVID-19 cases, Japanese government has continued to
report the current status, in which several waves can be observed [6]. The peak
of the 5th wave was seen on August 20, but it decreased sharply in August.
Regarding Tokyo, the capital of Japan, statistic result is shown. It dropped to
49 cases per day on October 11. After that, new case number in average (/day)
decreased as 34, 24 and 19 for 3 weeks, respectively. On November 7, the number
of deaths in Japan fell to zero after 15 months (Figure 1).
Similar to 50 states in
United States, Japan has 47 prefectures. In each prefecture, the number of new
COVID-19 cases have been checked every day for long period [6]. The infection
situation is summarized on Nov 6, 2021 period. Total new cases were 241 in
Japan with Tokyo 29, Osaka 39. Out of 47 prefectures, 20 prefectures showed
none (Figure 2).
Currently, the number of
new cases in Japan has been decreasing sharply. Detail statistic and
epidemiological study has been continued [7]. Regarding conventional matters
related to this situation, several points characteristic of Japan would be
summarized in the following.
·
Mild
lockdown: It is not official compulsory strategy, but government asks people to
control the activity [6].
·
Basic
infection control: People continue properly masks and hand washing for long.
Government, companies, school and all other organizations are usually
considering effective measures, and everyone is always cooperating for
restricted lifestyle.
·
High
vaccination rate: Japanese people have public mind and consideration to others,
and then people are willing to take vaccination [8]. Japan has 120 million
population. Half Japanese has completed twice vaccination on Sept 13, and 60%
completed on Oct 4, 2021 [6]. The number and ratio of vaccination on Nov 5,
2021 is as follows: the first vaccination was done in 98,487,956 (77.8%) and
the second completion was 92,556,990 (73.1%). Regarding elderly (>65 years
old), the first was 32,769,460 (91.6%) and the second was 32,480,692 (90.8%).
Thus, most elderly people have been vaccinated so far, and the younger
generation is currently vaccinated.
Figure 1:
Data of new COVID-19 cases from the world, Japan and Tokyo
1a: New cases
fluctuate during 400-800 thousand per day.
1b: Japan has 5 infection waves about every several
months.
1c: Tokyo has less than 50 new cases for 3 weeks.
Drastic decrease in
COVID-19 infection in Japan has been evaluated as a mystery from overseas, and
several hypotheses have been found [9].
·
Seasonal
effects: For seasonal changes, similar declines are also observed in the United
States and Germany. In these countries, infection spreads frequently in summer
and winter. During them, air conditioning is used and windows are not opened
frequently. In contrast, people tend to ventilate more and go outdoors in
spring and autumn.
·
2-month
cycle: In many countries, COVID-19 has shown some waves with increasing and
decreasing. The phenomena were said to be observed every 2 months [10]. Some
difference may exist between the original strain and current Delta strain. In
previous strains, one patient infected another 2.5 people in average. On the
other hand, Delta strains seem to infect 5-9 people [11]. Such highly
infectious Delta strains can spread rapidly and then may converge rapidly.
·
Pathogenicity:
There is a possibility that the nature of the Delta strain may be mutated so
far [12]. In other words, the infectivity of the Delta strain was certainly
strong at the beginning. However, the infectivity and the pathogenicity (the
ability to cause the disease) may be weakened since then. It is certain that
many people infected the Delta strain, but they may not been tested because of
asymptomatic.
A latest report has shown impressive perspective [13]. The renin–angiotensin–aldosterone system (RAAS) seems to play a crucial role in SARS-COV-2 infection [14]. For one of the main components of RAAS, it would be most striking that ACE2 is a prerequisite for SARS-COV-2 infection [15].
Figure 2: New COVID-19 cases from 47 prefectures in Japan (Nov 6, 2021).
Some investigators showed
the association between phenotypic expression of COVID-19 and a homolog of ACE2
(polymorphism of ACE1 gene), in particular with its severity [16]. For
explaining apparent mortality difference of Western and East Asian people, the ethnic
difference of ACE1 insertion (I)/deletion (D) polymorphism seems to be involved
[13]. Consequently, the investigation on ACE1 genotype will bring new clues to
diagnosis, pathophysiology and treatment for SARS-CoV-2 in the future [17]. In
summary, latest data and related topics for COVID-19 were described [18]. Some
description will be hopefully useful for clinical practice and research of COVID-19
in the future.
Conflicts
of interest
None.
Funding
None.
References
3.
Tokyo
Olympic and Paralympic.
5.
John
Hopkins University. The data showed 249,642,958 cases and 5,046,783 deaths on
November 7, 2021.
6.
MHLW
of Japan.
8.
Yoda T, Katsuyama H.
Willingness to receive COVID-19 vaccination in Japan. Vaccines. 2021; 9: 48.
10.
Covid,
in Retreat.
11.
COVID-19
vaccine breakthrough case investigations team. COVID-19 Vaccine breakthrough
infections reported to CDC - United States, MMWR Morb Mortal Wkly Rep. 2021;
70: 792-793.
15.
Tang
Q, Wang Y, Ou L, Li J, Zheng K, Zhan H, et al. Downregulation of ACE2
expression by SARS-CoV-2 worsens the prognosis of KIRC and KIRP patients via
metabolism and immunoregulation. Int J Biol Sci. 2021; 17: 1925-1939.