Vaccination: What It Is, How It Works, and Why It Matters

Introduction

Vaccines protect against illness, reduce complications, and save millions of lives every year¹. However, many people are still not completely aware of why vaccines are so important. While most people know that vaccines protect against diseases, they may not fully understand how they work or why some vaccines are recommended throughout life. 

So, if you’ve ever wondered, ‘what is a vaccine?’ this blog will help answer that question while explaining how vaccines work, the different types available, why are vaccines important​, and why staying up to date with recommended vaccinations is important for people of all ages. 

What Is Vaccination?

Vaccination is a safe and effective way to protect both individuals and communities from infectious diseases². It involves administering a vaccine (a weakened, inactivated, or harmless part of a germs ) that helps the body’s immune system recognise and fight the specific germ. It works by preparing the immune system in advance. This helps reduce the risk of developing serious illness if a person is exposed to the disease in the future³. 

Why Is Vaccination Done?

Vaccination is done to help prevent  infectious diseases before they occur. It trains the body’s immune system to recognise harmful germs and respond quickly if they enter the body³. Vaccines help reduce the risk of severe illness, complications, hospitalisation, and death caused by infectious diseases. They also help avoid the spread of infections within communities, protecting people who may be more vulnerable to disease⁴. 

How Do Vaccines Work?

Vaccines work by teaching the immune system how to recognise and fight harmful germs. The process can be explained in a few simple steps: 

• Step 1: The Vaccine Is Administered: A vaccine is given through an injection, oral dose, or nasal spray. It contains a weakened, inactivated, or harmless part of a germ³. 
• Step 2: The Immune System Responds: The body recognises the vaccine material as foreign and activates the immune system to produce protective antibodies and immune cells^3,5. 
• Step 3: Immune Memory Is Created: The immune system stores information about the germ, creating a ‘memory’ that helps it recognise the infection in the future³. 
• Step 4: Future Protection: If the vaccinated person is later exposed to the actual germ (virus or bacteria), the immune system quickly recognises it. It mounts a strong defence by fighting the germ, helping avoid illness or reduce its severity^3,5. 

Types of Vaccination

Vaccines are developed using different methods to help the immune system recognise and fight disease-causing germs. The main types of vaccines include: 

• Live Attenuated Vaccines: These vaccines contain a weakened form of the germs (virus or bacteria) that causes the disease. Because the germ is weakened, it does not usually cause illness in healthy people but still produces a strong immune response. 
  • Examples: Measles, Mumps, Rubella (MMR) vaccine, Chickenpox vaccine⁶. 
• Inactivated Vaccines: These vaccines contain germs that have been killed or inactivated. They cannot cause the disease but still stimulate the immune system to provide protection. 
  • Examples: Polio (IPV) vaccine, Hepatitis A vaccine, Rabies vaccine⁶. 
• Subunit, Recombinant, and Conjugate Vaccines: These vaccines contain only specific parts of a virus or bacterium, such as proteins or sugars, rather than the entire germ. This helps trigger an immune response while minimising side effects. 
  • Examples: Hepatitis B vaccine, Human Papillomavirus (HPV) vaccine, Pneumococcal vaccine⁶. 
• Toxoid Vaccines: Some bacteria cause disease by producing toxins. Toxoid vaccines contain inactivated toxins, helping the immune system learn how to defend against their harmful effects. 
  • Examples: Tetanus vaccine, Diphtheria vaccine⁶. 
• mRNA Vaccines: These vaccines use messenger RNA (mRNA) to provide instructions that help the body’s cells produce a harmless protein found on the germ. The immune system then learns to recognize and fight the actual infection. 
  • Examples: Certain COVID-19 vaccines. 
• Viral Vector Vaccines: These vaccines use a harmless virus, called a vector, to deliver genetic instructions that help the body produce an immune response against a specific disease. 
  • Examples: Some COVID-19 vaccines, Ebola vaccine⁶. 
• Combination Vaccines: Combination vaccines protect against multiple diseases with a single injection, reducing the number of shots required. 
  • Examples: DTaP vaccine (Diphtheria, Tetanus, and Pertussis), MMR vaccine (Measles, Mumps, and Rubella)⁶. 

Note: Different vaccines work in different ways, but all aim to train the immune system to recognise and respond more effectively to specific infectious diseases. 

Why Is Vaccination Important?

Vaccination is important because it helps protect individuals and communities from serious infectious diseases. Some of the key benefits of vaccines include: 

• Helps prevent many infectious diseases by helping the immune system recognise and fight harmful germs before they cause illness^2,3. 
• Reduces the risk of severe illness and complications associated with infectious diseases³. 
• Protects vulnerable individuals, such as infants, older adults, and people with weakened immune systems^3,8. 
• Helps avoid the spread of infections within families, schools, workplaces, and communities⁹. 
• Helps Contributes to herd immunity, which helps protect people who cannot receive certain vaccines for medical reasons². 
• Supports long-term public health by controlling and, in some cases, eliminating serious diseases³. 
• Reduces healthcare costs by avoiding illnesses that may require medical treatment or hospitalisation^4,10. 
• Protects future generations by limiting the circulation of infectious diseases in the population^2,3. 

Who Should Get Vaccinated and When?

Vaccination is recommended for people of all ages to help protect against infectious diseases. So, following the recommended immunisation schedule and receiving vaccines at the appropriate time helps ensure the best possible protection. Common recommendations include^11,12: 

1. Infants and Young Children

• Children should receive vaccines according to the recommended immunisation schedule. Early vaccination helps protect them from serious diseases during the years when they are most vulnerable. 
• Examples: Polio, DPT (Diphtheria, Pertussis, and Tetanus), Pneumococcal Conjugate Vaccine (PCV), Hepatitis B, Measles vaccines, etc. 

2. Adolescents and Teenagers

• Teenagers may need booster doses of certain vaccines as well as vaccines that are specifically recommended during adolescence. 
• Examples: HPV vaccine, Tetanus booster (Tdap), Meningococcal vaccine, etc. 

3. Adults

• Adults should keep their vaccinations and booster doses up to date to ensure continued protection against diseases that can be avoided with vaccines. 
• Examples: Annual Influenza (flu) vaccine, Tetanus booster (Td/Tdap), COVID-19 vaccines, etc. 

4. Pregnant Women

• Receiving recommended vaccines during pregnancy can help reduce the risk of certain infections for both the mother and her baby. So, pregnant women should consult their doctor regarding appropriate vaccinations. 
• Examples: Tdap vaccine and Influenza vaccine during pregnancy. 

5. People with Chronic Medical Conditions

• Individuals with conditions such as diabetes, heart disease, lung disease, kidney disease, or liver disease may be at higher risk of complications from infections and may require additional vaccines. 
• Examples: Influenza vaccine, Pneumococcal vaccine, Hepatitis B vaccine, etc. 

6. People with Weakened Immune Systems

• Individuals with weakened immunity due to cancers or medical treatments may need specific vaccinations to help reduce their risk of infection. Vaccination plans should be discussed with a healthcare professional. 
• Examples: Influenza vaccine, Pneumococcal vaccine, Shingles vaccine (where appropriate), etc. 

7. Healthcare Workers and Caregivers

• People who work in healthcare settings or provide care to vulnerable individuals should receive recommended vaccines to protect themselves and those they care for. 
• Examples: Hepatitis B vaccine, Influenza vaccine, COVID-19 vaccine, MMR vaccine, etc. 

8. Travelers

• People traveling to certain countries may require additional vaccines depending on the diseases present in the destination region. 
• Examples: Hepatitis A vaccine, Typhoid, Yellow Fever (where required), and other travel-related vaccines depending on destination.  

Important: The vaccines mentioned above are only examples. Not everyone needs the same vaccines at the same time. Your vaccination needs may depend on your age, health condition, lifestyle, occupation, and travel plans. Always consult your doctor and follow the recommended vaccination schedule to ensure you receive the appropriate vaccines at the right time. 

What Happens If You Don’t Get Vaccinated?

Choosing not to get vaccinated can increase the risk of contacting and spreading infectious diseases. While the level of risk varies depending on the disease and the individual’s health status, some potential consequences include: 

• Higher risk of infection because the immune system may not be prepared to recognise and fight specific germs¹³. 
• Increased risk of spreading infections to family members, friends, coworkers, and others in the community⁹. 
• Greater danger for vulnerable individuals, including infants and pregnant women, who may be more susceptible to severe disease⁸. 
• Reduced community protection (herd immunity), making it easier for infectious diseases to spread within the population¹⁴. 
• Increased risk of severe illness, complications, hospitalisation, or death from certain vaccine-preventable diseases 

Note: While not every unvaccinated person will become seriously ill, vaccination remains one of the safest and most effective ways to reduce the risk of many infectious diseases and their complications. 

Common Myths and Facts About Vaccination

Despite the proven benefits of vaccines, several myths and misconceptions continue to circulate. Therefore, understanding the facts behind these common claims can help people make informed decisions about vaccination and better protect their health. 

When Should You Get Vaccinated?

Vaccines should be received according to the recommended immunisation schedule and your doctor’s advice. 

Vaccination may be recommended during infancy, adolescence, adulthood, pregnancy, before travel, or in individual with certain health conditions that increase the risk of infection. Booster doses may also be needed over time to maintain immunity^11,12. 

In most cases, vaccines can be received at any time of the day. There is generally no specific morning, afternoon, or evening time that is considered best for vaccination. 

Note: Vaccination schedules vary based on factors such as age, health status, medical history, occupation, and travel plans. Always consult your doctor and follow the vaccination schedule recommended by national health authorities. 

Side Effects of Vaccines

Vaccines are generally safe and effective. However, they can sometimes cause side effects.  

Some of the common side effects after vaccination include¹⁶: 

• Pain, redness, or swelling at the injection site 
• Mild fever 
• Fatigue or tiredness 
• Headache 
• Chills 
• Muscle or joint aches 
• Mild rash (for some vaccines) 

Other, less common vaccine side effects include¹⁶: 

• Nausea or vomiting 
• Swollen lymph nodes 
• Dizziness or fainting 
• Temporary loss of appetite 
• Mild cold-like symptoms after certain vaccines (such as a runny nose or sore throat) 

Note: Most people experience either no side effects or only mild, short-lived symptoms after vaccination. The benefits of vaccination generally outweigh the risk of side effects. Always consult your doctor if you have concerns about vaccine safety or possible reactions. 

When to See a Doctor?

You should seek medical attention if you experience¹⁷: 

• Unusual confusion or extreme weakness 
• Difficulty breathing, wheezing, or noisy breathing 
• Difficulty swallowing or a feeling of tightness in the throat 
• Swelling of the face, throat, or tongue 
• Severe dizziness, fainting, or loss of consciousness 
• Pale, blue skin, lips, or tongue 
• Severe or unusual symptoms that do not improve 
• Any reaction that concerns you after vaccination 

Important: Vaccines are safe for most people. However, some individuals may not be able to receive certain vaccines, including those who have had a severe allergic reaction (anaphylaxis) to a previous vaccine dose or one of its ingredients. People with weakened immune systems due to certain medical conditions or treatments may not be eligible for some vaccines. If you are unsure whether a vaccine is suitable for you or your child, consult your doctor for guidance¹⁸. 

Also Read: Everything You Need to Know About the Hepatitis A Vaccine

Conclusion

Vaccination is one of the most effective ways to protect individuals and communities from infectious diseases. They help the immune system recognise and fight harmful germs, and reduce the risk of illness, serious complications, and disease outbreaks.  

If you have questions about which vaccines are right for you or your family, consult your doctor and follow the recommended immunisation schedule. 

Frequently Asked Questions (FAQs)

References

1. Why vaccines matter: understanding the broader health, economic, and child development benefits of routine vaccination – PMC. Accessed June 15, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC7482790/ 

2. Hussain S. Immunization and Vaccination. Psychiatry Pandemics. Published online May 16, 2019:153-177. doi:10.1007/978-3-030-15346-5_13. https://pmc.ncbi.nlm.nih.gov/articles/PMC11901362/ 

3. Ginglen JG, Doyle MQ. Immunization. In: StatPearls. StatPearls Publishing; 2026. Accessed June 15, 2026. http://www.ncbi.nlm.nih.gov/books/NBK459331/ 

4. Laupèze B, Del Giudice G, Doherty MT, Van der Most R. Vaccination as a preventative measure contributing to immune fitness. NPJ Vaccines. 2021;6:93. doi:10.1038/s41541-021-00354-z. https://pubmed.ncbi.nlm.nih.gov/34315886/ 

5. CDC. Explaining How Vaccines Work. Vaccines & Immunizations. May 7, 2026. Accessed June 15, 2026. https://www.cdc.gov/vaccines/basics/explaining-how-vaccines-work.html 

6. Policy (OIDP) O of ID and H. Vaccine Types. April 27, 2021. Accessed June 15, 2026. https://www.hhs.gov/immunization/basics/types/index.html 

7. Combination Vaccines – PMC. Accessed June 15, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC3068581/ 

8. Bruxvoort KJ, Bahakel H, Martin JM, et al. Inclusion of Women, Children, the Elderly, and Individuals With Underlying Medical Conditions: Prioritizing Vulnerable Populations in Clinical Research. Clin Infect Dis Off Publ Infect Dis Soc Am. 2025;81(Suppl 2):S78-S88. doi:10.1093/cid/ciaf408. https://pmc.ncbi.nlm.nih.gov/articles/PMC12513348/ 

9. Jung H, Albarracín D. Concerns for others increases the likelihood of vaccination against influenza and COVID-19 more in sparsely rather than densely populated areas. Proc Natl Acad Sci U S A. 2021;118(1):e2007538118. doi:10.1073/pnas.2007538118. https://pubmed.ncbi.nlm.nih.gov/33443183/ 

10. Benefits of vaccination. January 17, 2024. Accessed June 15, 2026. https://vaccination-info.europa.eu/en/about-vaccines/benefits-vaccination 

11. CDC. Vaccines by Age. Vaccines & Immunizations. June 9, 2025. Accessed June 15, 2026. https://www.cdc.gov/vaccines/by-age/index.html 

12. CDC. What Vaccines are Recommended for You. Vaccine Information for Adults. December 12, 2025. Accessed June 15, 2026. https://www.cdc.gov/vaccines-adults/recommended-vaccines/index.html 

13. Shaw D. The Side Effects of Not Being Vaccinated: Individual Risk and Vaccine Hesitancy Nationalism. J Bioethical Inq. 2022;19(1):7-10. doi:10.1007/s11673-021-10141-z. https://pmc.ncbi.nlm.nih.gov/articles/PMC8611634/ 

14. Field RI. Vaccine Declinations Present New Challenges for Public Health. Pharm Ther. 2008;33(9):542-543. https://pmc.ncbi.nlm.nih.gov/articles/PMC2730125/ 

15. What’s in a vaccine? Accessed June 15, 2026. https://www.who.int/news-room/feature-stories/detail/how-are-vaccines-developed 

16. CDC. Possible Side Effects from Vaccines. Vaccines & Immunizations. October 2, 2024. Accessed June 16, 2026. https://www.cdc.gov/vaccines/basics/possible-side-effects.html 

17. Anaphylaxis. nhs.uk. October 20, 2017. Accessed June 16, 2026. https://www.nhs.uk/conditions/anaphylaxis/ 

18. Why vaccination is important and the safest way to protect yourself – NHS. Accessed June 16, 2026. https://www.nhs.uk/vaccinations/why-vaccination-is-important-and-the-safest-way-to-protect-yourself/ 

19. Why vaccination is important and the safest way to protect yourself. nhs.uk. March 6, 2024. Accessed June 16, 2026. https://www.nhs.uk/vaccinations/why-vaccination-is-important-and-the-safest-way-to-protect-yourself/ 

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