太陽光は新型コロナウイルスを急速に不活性化させるのか？　論文の公開求める声も

【ワシントンＡＦＰ＝時事】太陽光は新型コロナウイルスを急速に不活性化させるのか？ 米ホワイトハウスは、政府機関による謎めいた研究結果を明らかにしてそう主張したものの、一部の科学者は、さらなる証拠が示されるのを待っている状態だとして注意を呼びかけている。（写真は資料写真）
　米国土安全保障省長官の科学技術顧問を務めるウィリアム・ブライアン氏は２３日、ドナルド・トランプ大統領のコロナ流行に関する定例会見で、太陽光によって新型コロナウイルスが急速に不活性化することが分かったと発表。この発表には多くの注目が集まった。
　実験は、米メリーランド州にある国立生物兵器分析対策センターで実施。ブライアン氏が記者団に対して示した実験結果をまとめたスライドによると、ステンレス製品などの無孔質の表面上にあるウイルス量の半減期は、気温２１～２４度、湿度８０％の暗所で６時間だったが、太陽光が当たると半減期は２分にまで縮まった。
　また新型ウイルスが空気中に漂う状態になった場合の半減期は、温度２１～２４度、湿度２０％の暗所で１時間だったが、太陽光が当たると１分半にまで減少した。
　太陽光に含まれているが目には見えない紫外線は、ある種の病原体の消毒に非常に効果があることが知られている。世界保健機関（ＷＨＯ）が発展途上国の人々に、水道水をプラスチックのボトルに入れて太陽の下に５時間置くよう推奨しているのもこのためだ。しかし、すべての病原菌が太陽光で死滅するとは限らない。
　太陽光には波長が違うさまざまな紫外線が含まれている。大まかに見ると、日焼けや肌の老化の原因となる紫外線Ａ波（ＵＶＡ）、紫外線Ａ波よりエネルギーが強く、肌がやけどのように赤くなったり、がんを引き起こしたりすることもある紫外線Ｂ波（ＵＶＢ）、そして最も危険な紫外線Ｃ波（ＵＶＣ）に分けられる。

■紫外線Ａ波、ＳＡＲＳウイルスの活性には影響なし
　地球の大気を透過して地上に到達する紫外線は主にＵＶＡ。ＵＶＣは大気に吸収されて地上には届かない。ＵＶＣは動物細胞やウイルスの遺伝物質を傷つける程度が特に強いため、これが地上に届かないのはわれわれにとって朗報だ。
　新型コロナウイルスと遺伝子学的に近い重症急性呼吸器症候群（ＳＡＲＳ）の原因ウイルスを調べた２００４年の研究で、ＵＶＡは照射時間の長短にかかわらず、ＳＡＲＳのウイルスの活性にまったく影響を与えないことが示された。通常は実験室や病院の消毒に用いられ、今では中国のバスの消毒にも使われているＵＶＣは、ＳＡＲＳのウイルスを１５分以内に完全に不活性化させた。
　新型コロナウイルス「ＳＡＲＳ-ＣｏＶ-２」が、ＳＡＲＳのウイルスよりＵＶＣだけでなく普通の太陽光にも弱い可能性はある。問題は、国土安全保障省が、科学界の規範を無視してデータを公開していないことだ。
　ウイルス疫学者のクリス・ボンシファルバ氏は、「どのように実験が行われたのかを知るために、研究について理解することが非常に重要となるだろう。実際の研究論文、または最低でも査読前の原稿がすぐに共有されることを強く期待している」 「科学界は彼らの発見を検討したがっているのは確かだ」と述べた。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2020/04/27-13:26）

Does sunlight rapidly destroy the coronavirus? A White House presentation on a mysterious government study says so -- but some scientists have called for caution as we await more evidence.
An official from the Department of Homeland Security made the eye-catching announcement during President Donald Trump's daily pandemic briefing Thursday, showing a dramatic reduction in the virus' viability under the sun's rays.
But the fact there are no further details about how the study was conducted has left some experts scratching their heads.
It looks like someone did a test somewhere, Benjamin Neuman, chair of biological sciences at Texas A&M University-Texarkana, told AFP.
It would be good to know how the test was done.
William Bryan, the official who summarized the findings, told reporters that an experiment was carried out at the National Biodefense Analysis and Countermeasures Center in Maryland.
On a stainless steel surface in sunlight, the virus shrinks to half its amount in a matter of just two minutes in 70 to 75 degrees Fahrenheit (21 to 24 degrees Celsius) heat and 80 percent humidity, compared to six hours in the dark.
When the virus was suspended in the air, its half-life in sunlight was just a minute and a half when the temperature was 70 to 75 degrees with 20 percent humidity, as opposed to one hour in the dark.
Beyond the headline results, there are so far few details, making it impossible for experts to independently validate the findings.
As a scientist, I'd of course like to see an actual study and the actual numbers, viral epidemiologist Chris von Csefalvay told AFP.
- The ABCs of sunshine -
We do know that the solar radiation contained in ultraviolet light -- an invisible, energetic part of the electromagnetic spectrum -- can be very effective at dealing with certain pathogens.
That is why, for example, the World Health Organization recommends that people in developing countries can place tap water in plastic bottles and leave them under the sun for five hours in order to make it drinkable.
But not all microbes respond in the same way.
Sunlight in fact contains different types of ultraviolet radiation, which are classed by their wavelength.
Broadly speaking, these can be categorized into UVA, which causes the skin to tan and age; UVB, which is a bit more harmful in high doses and can cause burning and cancer, and UVC, which is the most dangerous.
Most of the sunlight that penetrates our atmosphere is UVA while UVC is completely filtered out.
That is good news for us: UVC has small, high energy waves that are particularly adept at warping genetic material, whether in animal cells or in viruses.
A 2004 study on SARS -- a close genetic relative of the new coronavirus -- found that UVA light had no effect on viability, regardless of duration of exposure.
UVC light -- which is commonly used to sterilize labs, hospitals and now even buses in China -- completely inactivated the virus within 15 minutes.
- Moot point? -
It is entirely possible that the SARS-CoV-2 virus is more vulnerable to regular sunlight than its older cousin, and not just UVC.
The problem is the DHS has bypassed scientific norms by not making its data available -- even in its preliminary, non peer-reviewed form, which is how most major research during this pandemic has first made its way into the public domain.
It would be really important for understanding this study to know how it was conducted, and I am quite hopeful that the actual paper, or at least a pre-print, will be shared soon, said von Csefalvay.
I know for a fact that the scientific community is eager to review their findings.
But even if all the findings are airtight, solar disinfection is probably going to have a limited impact.
After all, people are less likely to be infected outdoors than indoors, unless they are directly coughed or sneezed upon -- in which case UV rays won't have time to inactivate the viral droplets before they hit their target.
On the other hand, UVB can help boost the immune system by causing the body to produce more Vitamin D.
All of this points to the need for more research. But one thing is clear: President Trump's suggestion that UV could be used to treat patients already infected with the virus isn't grounded in fact.
There is no way currently that UV could be used to irradiate inside the body that would do any good, Paul Hunter, a professor of medicine at the University of East Anglia said.