Vaccines: How They Protect Against Disease | 疫苗：如何预防疾病

📚 Vaccines: How They Protect Against Disease | 疫苗：如何预防疾病

Vaccination is one of the most effective ways to protect individuals and communities from infectious diseases. In this article, we will explore exactly how vaccines work, why they are so important, and how they fit into the IGCSE Biology syllabus for Edexcel.

疫苗接种是保护个人和社区免受传染病侵害的最有效方法之一。在本文中，我们将深入探讨疫苗的具体作用机制、它们为何如此重要，以及它们在 Edexcel IGCSE 生物课程中的地位。

1. Why Do We Need Vaccines? | 为什么我们需要疫苗？

The immune system defends the body against pathogens such as bacteria and viruses. When a pathogen enters the body for the first time, the immune response is slow because specific white blood cells (lymphocytes) have never met the pathogen before. During this delay, the pathogen can cause severe illness.

免疫系统负责防御细菌、病毒等病原体。当病原体第一次进入体内时，由于特定的白细胞（淋巴细胞）从未遇到过这种病原体，免疫反应非常缓慢。在这一延迟期间，病原体可能引发严重疾病。

Vaccines train the immune system in advance by introducing a harmless version of the pathogen. This means that if the real pathogen later attacks, the body is already prepared and can respond rapidly and effectively.

疫苗通过引入无害的病原体版本来预先训练免疫系统。这意味着，如果真正的病原体日后入侵，体内已经有所准备，能够快速有效地作出反应。

2. Key Terms: Antigens and Antibodies | 关键术语：抗原与抗体

Every pathogen carries unique molecules on its surface called antigens. These antigens are recognised as ‘foreign’ by the immune system, triggering a defensive response.

每种病原体表面都带有独特的分子，称为抗原。免疫系统将这些抗原识别为“外来物质”，从而触发防御反应。

In response to a specific antigen, lymphocytes produce antibodies. Antibodies are proteins that bind to the antigen, neutralise the pathogen, and mark it for destruction by other immune cells.

针对特定的抗原，淋巴细胞会产生抗体。抗体是能够与抗原结合的蛋白质，可用中和病原体，并标记它以供其他免疫细胞摧毁。

Antibody → binds specifically to antigen → neutralises pathogen

抗体 → 特异性结合抗原 → 使病原体失活

3. How Do Vaccines Work? | 疫苗是如何工作的？

A vaccine contains antigens from a pathogen, but the pathogen has been modified so it cannot cause disease. Common vaccine types include:

疫苗含有来自病原体的抗原，但病原体已被改造，无法致病。常见的疫苗类型包括：

Dead (inactivated) pathogens – killed by heat or chemicals, e.g. polio vaccine.
Live attenuated pathogens – weakened so they cannot cause serious illness, e.g. measles, mumps and rubella (MMR) vaccine.
Subunit vaccines – contain only part of the pathogen (e.g. a protein antigen), e.g. human papillomavirus (HPV) vaccine.

灭活病原体 – 通过加热或化学药品杀死，如脊髓灰质炎疫苗。
减毒活病原体 – 已弱化至不能引发严重疾病，如麻疹、腮腺炎和风疹（MMR）疫苗。
亚单位疫苗 – 仅包含病原体的一部分（如蛋白质抗原），如人乳头瘤病毒（HPV）疫苗。

After vaccination, the immune system treats the antigens as an invader and produces antibodies. Some lymphocytes become memory cells, which remain in the body for many years – sometimes for life.

接种疫苗后，免疫系统将抗原视作入侵者并产生抗体。部分淋巴细胞会变成记忆细胞，这种细胞在体内可存留多年，有时甚至终身存在。

If the individual later comes into contact with the real pathogen, memory cells divide rapidly to produce large amounts of antibodies very quickly. The pathogen is destroyed before it can cause significant symptoms.

如果此人日后接触到真正的病原体，记忆细胞会迅速分裂，快速产生大量抗体。病原体在引发显著症状之前就被摧毁了。

4. Active Immunity: Natural and Artificial | 主动免疫：天然与人工

Vaccination produces active immunity, because the body’s own immune system becomes actively involved in making antibodies. Compare this with passive immunity, where antibodies are given directly.

疫苗接种产生主动免疫，因为机体自身的免疫系统积极参与抗体产生。这与直接给予抗体的被动免疫不同。

Type	How it is acquired	Duration	Example
Natural active	Infection with pathogen	Long-term	Chickenpox → immunity
Artificial active	Vaccination	Long-term	Hepatitis B vaccine
Natural passive	Antibodies passed from mother to baby	Short-term	Breast milk, placenta
Artificial passive	Injection of antibodies (immunoglobulin)	Short-term	Tetanus antitoxin

In each case, the key difference is whether memory cells are produced. Active immunity produces memory cells, while passive immunity does not.

每种情况下，关键区别在于是否产生记忆细胞。主动免疫会产生记忆细胞，而被动免疫不会。

5. Herd Immunity | 群体免疫

When a large percentage of a population is vaccinated, the pathogen cannot easily spread because most people are immune. This is called herd immunity. It also protects people who cannot be vaccinated, such as babies, pregnant women, or those with weakened immune systems.

当人群中很大比例的人都接种了疫苗，病原体就不易传播，因为大多数人已免疫。这被称为群体免疫。它还能保护无法接种疫苗的人群，例如婴儿、孕妇或免疫系统较弱的人。

For herd immunity to work, a high vaccination uptake is needed. If vaccination rates drop, outbreaks of diseases such as measles can occur.

为了实现群体免疫，需要很高的疫苗接种覆盖率。如果接种率下降，麻疹等疾病就可能爆发。

6. The Vaccination Process: Step by Step | 接种疫苗的步骤

From an exam perspective, you should be able to describe the sequence of events after vaccination:

从考试的角度，你应该能描述疫苗接种后的事件顺序：

A vaccine containing antigens (dead, weakened or part of a pathogen) is injected or taken orally.
White blood cells (lymphocytes) recognise the antigens as foreign.
Lymphocytes produce antibodies that specifically fit the antigen.
Some lymphocytes become memory cells that remain in the blood.
On later infection, memory cells rapidly produce many antibodies, preventing illness.

注射或口服含有抗原的疫苗（死病原体、弱化病原体或病原体片段）。
白细胞（淋巴细胞）将抗原识别为外来物质。
淋巴细胞产生与该抗原特异性匹配的抗体。
部分淋巴细胞成为记忆细胞，留存于血液中。
日后感染时，记忆细胞快速产生大量抗体，从而防止发病。

7. Pros and Cons of Vaccination | 疫苗接种的利与弊

Vaccination has transformed public health. But it is also worth understanding some of the perceived drawbacks, as these may appear in exam questions about discussions or debates.

疫苗接种极大地改善了公共健康。但了解一些可能存在的缺点也很有价值，因为这可能出现在关于讨论或辩论的考题中。

Advantages	Disadvantages / risks
Provides lasting immunity	Can cause mild side effects (e.g. sore arm, fever)
Protects individuals and communities	Rare allergic reactions
Can eliminate diseases (e.g. smallpox)	Vaccines are not always 100% effective

Overall, the benefits of vaccination far outweigh the risks for almost everyone.

总体而言，对几乎所有人来说，接种疫苗的好处远大于风险。

8. Common Exam Pitfalls | 常见考试误区

Students often confuse vaccination with giving antibodies. Remember: a vaccine triggers the body to make its own antibodies, so it is an example of artificial active immunity.

学生常把疫苗接种与直接给予抗体混为一谈。请记住：疫苗是触发身体自行产生抗体，因此属于人工主动免疫。

Another trap is thinking vaccines only contain antibodies. Actually vaccines contain antigens (not antibodies). The body then produces antibodies in response.

另一个陷阱是认为疫苗只含有抗体。实际上，疫苗含有抗原（不是抗体）。身体随后对之反应产生抗体。

Finally, memory cells are the reason why a second exposure to a pathogen is much quicker than the first. This is the basis of the ‘booster dose’, which restores memory cell numbers.

最后，记忆细胞是第二次接触病原体比第一次反应快得多的原因。这也是“加强针”的基础，它可恢复记忆细胞数量。

9. Revision Summary | 复习总结

Use this summary to check you have covered the main points from Edexcel IGCSE Biology 2.64:

使用以下摘要检查你是否掌握了 Edexcel IGCSE 生物 2.64 的主要要点：

Vaccines contain antigens from a harmless pathogen.
The immune system produces antibodies and memory cells.
On real infection, memory cells produce a rapid antibody response.
Vaccination is artificial active immunity.
Herd immunity protects the unvaccinated.

疫苗含有来自无害病原体的抗原。
免疫系统产生抗体和记忆细胞。
真正感染时，记忆细胞迅速产生抗体反应。
疫苗接种是人工主动免疫。
群体免疫保护未接种者。

Now you should be confident in explaining how vaccines protect individuals from disease. Keep revising the key terms – antigens, antibodies, memory cells and active immunity – and you will be ready for any IGCSE question on this topic.

现在你应该能够自信地解释疫苗如何保护个体免受疾病侵害。继续复习关键术语——抗原、抗体、记忆细胞和主动免疫——你就能从容应对任何关于这一主题的 IGCSE 考题。

Published by TutorHao | Biology Revision Series | aleveler.com

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Vaccines: How They Protect Against Disease | 疫苗：如何预防疾病