Mutant virus "Spreading cannot be suppressed unless human contact is" halved ""

Recently NHK News on-line reported the following:

変異ウイルス「人の接触“半分減”でないと拡大抑えられず」

04月15日　22時44分

東京都内で感染力が強い変異ウイルスが広がった場合、人と人との接触を半分程度まで減らさないと感染拡大を抑えられないとする分析結果を都の専門家がまとめました。

分析結果は、１５日のモニタリング会議で、都の「専門家ボード」の座長を務める東北医科薬科大学の賀来満夫特任教授が明らかにしました。

今回の分析は、１人の感染者が何人に感染を広げるかを示す「実効再生産数」が、感染力が強いとされる「Ｎ５０１Ｙ」の変異があるウイルスの場合、従来のウイルスの１.４３倍になるとして計算しました。

１.４３倍は国立感染症研究所の報告をもとに仮定した数値です。

その結果、「Ｎ５０１Ｙ」の変異があるウイルスが広がった場合、人と人との接触を３０％減らしても、１人が１.１人に広げることになり、感染は拡大するとしています。

一方、接触を５０％減らした場合は１人が広げるのは０.７９人で、半分程度まで減らさないと感染拡大を抑えられないとしています。

さらに、７０％減らした場合は０.４７人まで減少し、感染の抑制につながるとしています。

ただ、海外の研究では「Ｎ５０１Ｙ」の変異があるウイルスの場合、「実効再生産数」が従来のウイルスの１.９倍だという報告もあります。

この場合、人との接触を５０％減らしても感染が拡大する計算になるということです。

賀来特任教授は「大阪のように新規陽性者が急増する前に、東京でも徹底して人の流れを減らしていくことがいっそう必要だ」と述べました。

Translation

Experts in Tokyo had summarized the analysis results showing that if a highly infectious mutant virus spread in Tokyo, the spread of the infection could not be suppressed unless the contact between people was reduced by about half.

The analysis result was revealed at the monitoring meeting on the 15th by Professor Mitsuo Kaku of Tohoku Medical and Pharmaceutical University who chaired the "Expert Board" in Tokyo.

In this analysis, the "Effective reproduction number" which indicated how many people one infected person would spread to another was calculated; in the case of a virus with a mutation of "N501Y" which was said to have strong infectivity, it was calculated to be at 1.43 times that of the conventional viruses.

1.43 times was the value assumed based on the report of the National Institute of Infectious Diseases.

As a result, if a virus with the "N501Y" mutation spread, even if the contact between people was reduced by 30%, one person could spread to 1.1 people, and the infection would spread out.

On the other hand, if the contact was reduced by 50%, one person would spread to 0.79 people, and so it was said that the spread of infection could not be suppressed unless human contact is reduced to about half.

Furthermore, if it was reduced by 70%, spreading would be reduced to 0.47, which could lead to the suppression of infection.

However, in overseas research, it had been reported that the "Effective reproduction number" of a virus with a mutation of "N501Y" was 1.9 times that of a conventional virus.

In this case, even if the contact between humans was reduced by 50%, the infection could still spread.

Professor Kaku said, " Tokyo need even more thorough reduction in the flow of people,  before the number of new positive cases increase rapidly as happening in Osaka."

              So,  in Osaka, the virus with the "N501Y" mutation is spreading in high speed and number not seen before. Leaders in Tokyo are under pressure to implement tougher regulations to control human flow so as to avoid this spreading in the capital area.