令和 3 年 8 月 31 日
ワクチン接種後も「感染予防対策徹底」の継続を
金沢大学長 山崎光悦
学生の皆さん
本学では,医療従事者をはじめ多くの職員の協力を得て,新型コロナワクチンの大学拠点(職域)接種を7月6日に開始し,8月27日に終了しました。本学学生・教職員の接種希望者に加え,職域接種を実施しない近隣の大学関係者なども対象としました。本学が地域一般より早く接種を開始でき,皆さんがワクチン接種に関する正しい知識に基づいて判断した結果,学生全体の接種率は,自治体等での接種希望も含めると88%に達する見込みです。これは,私たち自身と共に社会を守るための寄与でもあり,一日も早いコロナ禍収束への一助となることを願っています。
石川県では,第4波が収束したとみられる6月26日には新規感染者はゼロになり,感染者の累計では,6月末日までは4千人未満(3,931人)でした。しかし,その後急激に感染が拡大し,7月28日には1日としては過去最多の119人の新規感染者が確認され,県はモニタリング指標を最も深刻な「ステージ4(感染拡大緊急事態)」に引き上げ,国に対するまん延防止措置の要請も決めました。7月の1か月間の感染者は1,174人でしたが,8月の1か月間では2倍近くの2千人を超えました(8月29日現在:2,080人/随時更新)。このような急激な感染拡大は,感染力の強い変異株「デルタ株」への置き換わりが進んだためとみられています。実際,県内のデルタ株の割合は,6月は1.3%でしたが,7月に40%に上昇し,8月には81.4%に達しています(※1:8月25日石川県公表)。
WHO(世界保健機関)によると,デルタ株は2020年10月に初めて報告され,2021年4月以降の爆発的な感染拡大の原因の1つとみられています。感染力が強く,従来の新型コロナウイルスのおよそ2倍,日本国内の感染拡大の第4波で広がったアルファ株の1.5倍程度と言われています。
ここで,ワクチン接種後の「ブレークスルー感染」について詳しく書きます(※2:厚生労働省Webより)。ウイルスや細菌に一度感染すると,身体の中にその病気に対する抵抗力(免疫)がついて,この記憶は身体の中に長く残ります。このため,麻疹や水痘など多くの感染症は「一度かかると二度とかからない」と言われています。しかし,インフルエンザなど,少しずつ性質を変化させる病原体による感染症は,ワクチンを接種した後でも感染する可能性があり,これを「ブレークスルー感染」と呼びます。
麻疹や水痘では鼻や喉の粘膜からウイルスが侵入した後,扁桃や近くのリンパ節でウイルスが増え,ついで血液の流れに乗って全身にウイルスが拡がってから,発熱や発疹などの症状が現れ発症します。つまりウイルスが体内に入り込んでから発症するまでの間に,10~20日間程度の潜伏期があります。既に感染していたり,ワクチンを接種したりして免疫ができている人では,血液中の抗体がそこに入ってきたウイルスをブロックするので,発症しなくて済みます。一方,インフルエンザの場合,鼻や喉の粘膜に侵入したウイルスは,そこですぐに増殖を始め呼吸器粘膜を傷害して,数日で発症します。ワクチンを接種して血液中に抗体があっても,呼吸器粘膜の感染を防ぐことは難しく,発症を防ぐ機能も十分ではありません。しかし抗体は肺の中に滲み出てきて肺炎を起こさないようにブロックすることで,重症化を防ぎます。新型コロナウイルスもインフルエンザウイルスと同じように,鼻や喉の粘膜で増えて数日で発症します。さらに肺にまで感染が及ぶと重症化の恐れがあります。つまり,血液の中の抗体は鼻や喉の粘膜ではワクチンの効き目が弱く,感染を防ぐ効果は十分強くありませんが,肺では重症化を防ぐ効果を発揮するのです。
ワクチン接種を済ませた人のブレークスルー感染はデルタ株に置き換わった後で増えてきているものの,ワクチンによって重症化を防ぐ効果は高いレベルが保たれています。このことは,医療体制の逼迫を防ぎ,医療本来の機能の維持にもつながります。
このように,新型コロナウイルス感染症の感染予防や重症化抑制にはワクチンが効果的です。しかしながら,12歳未満の子供や,体質や基礎疾患のためにワクチンを接種できない方もいます。ワクチンを接種した人は,たとえ感染したとしてもほとんどの場合,重症化まで至りません。また,感染しても発症しないことが多いので,自分ではそれと気付かないまま他の人に感染を広げる恐れがあります。
ワクチン接種を2回済ませた人も,全ての人を守るために不要不急の移動は控え,これまで以上に,基本的な感染予防対策(マスク着用,手指消毒,密閉・密集・密接な環境の回避等)を徹底してください。
本学では皆さんの協力を得てワクチンの職域接種を終了できました。引き続き学生一人一人が感染予防対策を講じることにより,10月からの第3クォーターの対面授業を安全に再開し,以前のような日常の学生生活を取り戻すことができるものと期待します。改めて皆さんのご理解とご協力をよろしくお願いします。
※1: https://www.pref.ishikawa.lg.jp/kansen/variant.html
※2: https://www.cov19-vaccine.mhlw.go.jp/qa/column/0006.html
August 31, 2021
Continue to take " COVID-19 Infection Prevention Measures " even after vaccination
YAMAZAKI Koetsu
President, Kanazawa University
Dear Students,
With the cooperation of many staff members, including medical personnel, Kanazawa university implemented the workplace vaccination against COVID-19 from July 6 through August 27. In addition to our students, faculty, and staff who wished to be vaccinated, we also offered the vaccines to people from neighboring universities and other institutions that do not offer the workplace vaccination. Our university was able to start vaccinations earlier than the general public in the region. As a result of everyone’s decision based on proper knowledge of vaccination, the overall vaccination rate for students is expected to reach 88%, including those vaccinated by the local government. This contributes to the protection of society as well as ourselves, and I hope that it will help to bring the corona disaster under control as soon as possible.
In Ishikawa Prefecture, the number of new positive case dropped to zero on June 26, when the fourth wave of COVID-19 seemed to be under control, and the total number of infected people was less than 4,000 (3,931) until the end of June. However, since then, the infection has spread rapidly. On July 28, a record number of 119 new cases were confirmed in one day. Ishikawa Prefecture has decided to raise its monitoring index to Stage 4, the most serious, and requested the government to take "Priority Preventative Measures”. In the month of July, the number of new positive case was 1,174, but in the month of August, the number nearly doubled to over 2,000.( As of August 29: 2,080/ frequently updated )
This is believed to be caused because delta variant, the mutant strain with highly contagious, has replaced the conventional new coronavirus. In fact, the percentage of delta strain in the prefecture was 1.3% in June, rose to 40% in July, and reached 81.4% in August. (*1: announced by Ishikawa Prefecture on August 25).
According to the WHO, the delta strain was first reported in October 2020 and is considered as one of the causes that the disease has spread explosively since April 2021. It is said that the delta strain is twice as infectious as the conventional new coronavirus and about 1.5 times as infectious as the alpha strain, which spread in the fourth wave of infection in Japan.
Here, I would like to mention in detail about "breakthrough infection" after vaccination (*2: from the Ministry of Health, Labor and Welfare Web site). Once we are infected with a virus or bacteria, our body develops resistance (immunity) to the disease, and this memory remains in the body for a long time. For this reason, many infectious diseases, such as measles and chicken pox, are said to be "once you get it, you never get it again. However, infectious diseases caused by pathogens that gradually change their properties, such as influenza, can be transmitted even after vaccinated, and this is called "breakthrough infection".
In the case of measles and chickenpox, the virus enters the body through the mucous membranes of the nose and throat, increases in the tonsils and lymph nodes around them, and then spreads through the bloodstream to the entire body, causing symptoms such as fever and rash. In other words, there is an incubation period of about 10 to 20 days between the time the virus enters the body and the onset of symptoms. In people who have already been infected or vaccinated and are immune to the disease, the antibodies in the blood block the virus from entering the body, so they do not develop the disease. On the other hand, in the case of influenza, viruses that invade the mucous membranes of the nose and throat immediately begin to grow and damage the mucous membranes of the respiratory tract, resulting in the onset of illness within a few days. Even with antibodies in the blood after vaccination, it is difficult to prevent infection of the mucous membranes of the respiratory tract, and the ability to prevent the onset of illness is not sufficient. However, antibodies seep into the lungs to block the infection from causing pneumonia, thereby prevent serious illness. Like the influenza virus, the new coronavirus grow in the mucous membranes of the nose and throat and develops in a few days. If the infection spreads to the lungs, it can cause severe illness. In other words, antibodies in the blood are not effective enough to prevent infection in the mucous membranes of the nose and throat, but they are effective in the lungs to prevent serious illness.
Although the number of “breakthrough infections” in vaccinated individuals has increased since the replacement of the delta strain, the vaccine has been maintaining a high level of efficacy in preventing serious infections. This prevents the medical system from overwhelmed and helps them to maintain the original function of medicine.
Thus, vaccines are effective in preventing infection and reducing the severity of COVID-19 infections. However, there are some people who cannot be vaccinated, such as children under the age of 12 and people with constitutional or underlying medical conditions. In most cases, people who have been vaccinated will not become seriously ill even if they are infected. In addition, even if they are infected, they often do not develop symptoms, so they may spread the disease to other people without realizing it.
Even if you have been vaccinated twice, in order to protect everyone, please refrain from unnecessary travels and take basic infection prevention measures (wearing masks, disinfecting hands, avoiding closed, crowded, or close environments, etc.) more thoroughly than before.
At Kanazawa University, we have finished the workplace vaccination with your cooperation. We hope that by continuing to take infection prevention measures, we safely resume face-to-face classes in the third quarter starting in October and go back to the daily student life as before. I would appreciate your continued understanding and cooperation.
*1: https://www.pref.ishikawa.lg.jp/kansen/variant.html (Japanese only)
*2: https://www.cov19-vaccine.mhlw.go.jp/qa/column/0006.html (Japanese only)