TOKYO -- As the recent ratio of COVID-19 patients with severe symptoms has dropped compared to the first wave of infections between March and May, some media and internet users have suggested that the virus is weakening. But experts in Japan say that there is scant evidence of this, and are warning people not to let their guard down.
A resurgence of novel coronavirus infections has recently been observed in large urban areas of Japan including Tokyo, Osaka in the west and Aichi in the central part of the country. Nationwide, the daily number of new infections reached 1,239 on July 29, topping 1,000 for the first time. The tally of new cases has subsequently topped 1,500 on high days, with figures over twice as high as those observed during the first wave in April when Japan was placed under a state of emergency. Meanwhile, although a mild increase has been observed in the number of patients with severe symptoms, the figure as of Aug. 16 stood at 232, only around two-thirds of the single-day high of 328 recorded on May 1.
From such circumstances, there have been suggestions online that the virus has weakened. In particular, a doctor who has provided frontline treatment to coronavirus patients in Italy, which saw an explosive increase in cases, has since May stated in interviews with numerous foreign news outlets that the potency of the virus has weakened compared to March and April, among other arguments. Theories that quote the Italian doctor to claim the virus is now not as strong have spread since.
It seems that the virus has in fact been steadily undergoing change. A team including researchers from the Los Alamos National Laboratory and Duke University revealed that it noticed a mutation in the "spike protein" on the surface of the novel coronavirus, and published its findings this July in the U.S. medical journal Cell. It is reportedly estimated that the ability of the mutated virus to infect human cells is three to six times higher than that of the dominant strain of the virus observed in initial periods.
Furthermore, according to the National Institute of Infectious Diseases in Japan, virus samples found in the country up until mid-June had apparently undergone changes in six places of its ribonucleic acid (RNA) base sequence compared to the "European lineage" virus strain which spread throughout Japan from mid-March. The institute says, however, that the genetic information alone is not enough to determine how lethal the virus is.
In general, a virus evolves as it multiplies continuously, and spreads further by becoming less lethal and more transmissible. If the virus remains highly lethal, the death rate of patients, or hosts of the virus, will rise, making the virus less likely to spread and quickening its containment. On the other hand, if the virus weakens, it becomes able to spread easily throughout society, prolonging the outbreak period.
Nevertheless, experts say vigilance is still needed, as there is insufficient evidence of the coronavirus having weakened at present. Tetsuya Mizutani, a virology professor at Tokyo University of Agriculture and Technology, touched on the gradual decline in global death rates of coronavirus patients, and commented, "The possibility that the virus is heading in the direction of becoming weaker cannot be denied." However, he also emphasized, "Mutations occur randomly. It is also possible for the virus to transform suddenly and become more lethal. It's premature to pass judgement at the present stage." He also pointed out, "The coronavirus has an enzyme that can restore it to its original state before genetic mutation, and even if it does weaken, it will likely be to a very small degree. The fact that it poses a threat to elderly people and those with underlying diseases, who have a higher risk of developing severe symptoms, remains unchanged.
Toshimasa Hayashi, deputy head of the infectious diseases department at Maebashi Red Cross Hospital, warned against optimism that the virus has gotten weaker, saying, "It is dangerous to carelessly think that the virus has weakened." He explained that among reasons why there are relatively fewer patients with severe symptoms are improvements in treatment methods and the slow development of severe symptoms among patients.
During the first wave of infections, the number of individuals with severe symptoms peaked about three weeks after the number of new infection cases reached a high. This is because in most cases of pneumonia, there is a time lag of around 10 days between the day patients develop symptoms and when they require artificial respirators and extracorporeal membrane oxygenation (ECMO) equipment. Hayashi commented, "If infections spread to the elderly, the number of patients with severe symptoms will certainly increase. We absolutely must not let our guard down."
A staff member at a hospital in Tokyo is wary about the situation now, saying, "The number of patients with severe symptoms has in fact been gradually rising." The worker said the hospital is responding to a resurgence of infections while coping with financial damage following the first wave of cases, as the number of regular patients declined. "We are under a more strained situation than during the previous wave of infections," the staff member said.
(Japanese original by Ayumu Iwasaki, Science & Environment News Department)