Q1. What is the passage mainly about?

1. AHow to stop chickenpox in children
2. BWhy people in Wales live longer
3. CA study about a shingles vaccine and dementia
4. DHow doctors make new vaccines

帯状疱疹ワクチンと認知症の関係を調べた研究が全体の話題なので C。

Q2. Who could get the vaccine in Wales?

1. APeople born on or after September 2, 1933
2. BPeople born before September 2, 1933
3. COnly children in Wales
4. DOnly doctors and nurses

people born on that day or later could とあり、that day は1933年9月2日を指すので A。それより前に生まれた人は受けられなかった。

Q3. In this passage, "almost the same" means ...

1. Acompletely different
2. Bvery similar
3. Cmuch older
4. Dmuch healthier

almost は「ほとんど」、the same は「同じ」。その日の近くに生まれた人どうしはワクチン以外ほぼ同じ＝とても似ている、なので B。

Q1. Why is it difficult to study whether vaccines lower the risk of dementia?

1. ABecause vaccines are too expensive.
2. BBecause there are not enough patients with dementia.
3. CBecause doctors in Wales refused to help.
4. DBecause people who get vaccines may already be healthier in other ways.

第2文 people who choose to get vaccines may already take better care of their health が理由なので D。

Q2. What percentage of people born one week after the cutoff date got the vaccine?

1. A47.2 percent
2. B20 percent
3. C0.01 percent
4. D3.5 percent

47.2 percent of those born one week after it did とあるので A。20%は認知症の診断が減った割合。

Q3. Why does the passage call the researchers' method "a clever way around this problem"?

1. AIt allowed them to give the vaccine to everyone.
2. BIt made the study much cheaper than other studies.
3. CIt let them compare two groups that differed mainly in vaccination.
4. DIt proved exactly how the vaccine protects the brain.

these people were so similar in other ways, the researchers could compare them fairly とあり、違いがほぼワクチンだけの2群を比べられた点が「巧み」なので C。

Q1. What problem did the natural experiment help the researchers avoid?

1. AThe high cost of electronic health records
2. BConfounding caused by differences in health awareness
3. CThe lack of a shingles vaccine in Wales
4. DThe difficulty of measuring people's ages

第1文で People who get vaccinated tend to be more health-conscious … hard to trust と問題を示し、found a way around this problem としているので B。

Q2. Which of the following is true according to the passage?

1. AThe effect was stronger in men than in women.
2. BPeople born before September 2, 1933, became eligible a year later.
3. CThe study tested the vaccine that is most common today.
4. DVaccination lowered the chance of a new dementia diagnosis by about 20 percent.

by 3.5 percentage points, or about 20 percent とあるので D。効果は女性で強く（A×）、9月2日より前の人は never eligible（B×）、調べたのは older live vaccine（C×）。

Q3. Which is NOT mentioned as a weakness of the study?

1. AThe vaccine studied was an older type.
2. BNo one knows how the vaccine might protect the brain.
3. CA diagnosis depends on whether a person saw a doctor.
4. DThe two groups had very different lifestyles.

弱点として older live vaccine、nobody knows how the shot might protect the brain、a diagnosis depends on whether someone saw a doctor の3つが挙げられている。2つのグループは should be almost identical in lifestyle とされているので D が正解。