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Japan expert predicts coronavirus infections will peak April-May, last until August

Mitsuo Kaku is seen talking about the circumstances and potential developments associated with the new coronavirus, at Tohoku Medical and Pharmaceutical University's Fukumuro Campus in Sendai, on March 4, 2020. (Mainichi/Issei Takizawa)

SENDAI -- The coronavirus continues to spread across Japan, and fears it will take hold in communities are on the rise. To find out how the situation could develop, the Mainichi Shimbun spoke to Mitsuo Kaku, one of Japan's leading infectious disease experts. Kaku previously served as president of the Japanese Society for Infection Prevention and Control, and is currently a specially appointed professor at Tohoku Medical and Pharmaceutical University.

The interview was conducted on March 4, and the information included is current up to that day.

Question: What do we know about the new coronavirus?

Mitsuo Kaku: It has an incubation period of between one and 12 1/2 days. About 80% of patients experience mild symptoms, but conversely, it has a mortality rate of 3.8% and can easily trigger severe symptoms in people who are older or have preexisting conditions.

It's less infectious than influenza, yet the mortality rate is higher. But the data we're referring to here is all based on case histories from China, the alleged epicenter of the virus outbreak. The data from Japan must be closely inspected going forward.

Q: What's the state of infections?

At the moment we're at the initial stage of the spread of infections. The majority of infection routes so far have been from close physical contact. There have also been cases of droplet transmission, but many instances of infection are taking place in enclosed spaces.

Q: A man in his 70s who lives in the northern Japan city of Sendai and was a passenger on the Diamond Princess cruise ship was confirmed to have been infected after his return. Do you think we'll see more connected cases across northeastern Japan?

MK: The man in question wore a mask when going out, and reportedly only went to two shops for brief periods. The chances of him having spread the virus are low. But there is the possibility that someone other than this man is spreading the virus.

Q: What's your assessment of the Japanese government's initial steps to prevent infections at its borders?

MK: There's a very high chance that the virus was already being spread by people from the Chinese city of Wuhan in December 2019 (before information about the virus emerged), so infected people may have passed through controls at the border. Preventative measures at borders have been limited solely to body temperature checks, and I think it was difficult to effectively carry out such measures using that alone.

Q: The response to the handling of the cruise ship was divisive too. What do you think?

MK: The passengers and crew comprised various nationalities, and it was our first experience of group infection on a large vessel with some 3,700 people onboard. It's difficult to implement thorough hygiene controls in a space where space is limited, and there are many railings and other objects people touch with their hands.

Even bringing people off the ship would have posed problems, as there aren't facilities or checks to handle more than 3,000 people on Japanese soil.

Q: The government has asked all schools to close temporarily, and some local bodies have asked people to refrain from going outside. Have these measures been correct?

MK: Schools are the places where people have the highest risk of infection after their own homes. We don't yet know what effect it will have, but I understand that it was a viable choice, given the talk that this one- to two-week period could be the most important (to prevent the virus spreading). What's vital is that measures against infection such as closing the schools and refraining from going outside, are done in conjunction with each other.

Q: When do you expect the outbreak to peak, and when do you expect it to end?

MK: SARS was identified in November 2002, and its peak came around March and April 2003. In July of that year it was announced that the spread had ended. If we think about it on the same lines, then the new coronavirus began in around December 2019, and therefore would be expected to peak between April and May 2020, and continue until August.

The chances of it carrying on past summer are low, but we don't know what will happen. I think we'll be able to see whether the current countermeasures were effective by the end of March. It should gradually become clear how long the outbreak will last.

Q: Do you think that efforts in response to infections in Miyagi Prefecture, where you are based, have been sufficient?

MK: We don't have sufficient depressurized rooms (to prevent infection), and from an equipment perspective, things are looking very difficult. But the relevant institutions and bodies are working together to organize their response, so I want people to remain calm.

Additionally, systems to get people checked for whether they are infected with Polymerase Chain Reaction (PCR) tests are not catching up with demand. Given the current state of things, as of now I don't think it is a mistake to be prioritizing people with a high risk of developing severe symptoms, such as the elderly and those with existing conditions.

Q: What do you think is going to happen next?

MK: It's the first time that a coronavirus that can cause heavy symptoms has entered Japan, so there are many things we don't know yet. It is essential that researchers and experts commit to releasing scientifically-backed information, and that efforts are made to ensure testing is expanded and improved.

Q: What do you think about activities which aren't directly related to the spread of the virus, such as people buying up toilet and tissue paper?

MK: If the correct information isn't out there, then it leads to this kind of panic buying. To help the public avoid being taken in by fabrications, the government must provide information about what's going on.


Mitsuo Kaku was born in Oita Prefecture, southwestern Japan, in 1953. He completed his doctorate at Nagasaki University Graduate School of Medicine. He was previously an associate professor at St. Marianna University School of Medicine in the Kanagawa Prefecture city of Kawasaki and as a professor at Tohoku University School of Medicine, among other posts.

He took up his current position in 2019. Kaku specializes in the study of infectious diseases, and from March has headed the team of experts on the Nippon Professional Baseball Organization and J. League soccer body's new coronavirus prevention liaison committee.

(Interviewed by Issei Takizawa, Sendai Bureau)

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