How Vaccines Work: Live vs Inactivated Vaccines Explained

Vaccines are one of the greatest success stories in modern medicine. But how do they actually work to protect us from serious diseases?

At Ready Health Clinic, we offer expert vaccination advice and services as part of our travel health and general health support. In this blog, we’ll break down the science behind vaccines in a simple, friendly way—so you can feel informed, confident, and prepared.

What Is a Vaccine?

A vaccine trains your immune system to recognise and fight off harmful organisms—like viruses and bacteria—before they can make you seriously unwell.

Vaccines work by creating active immunity, which means your body makes its own immune response. They also help create immunological memory, so if you're exposed to the real infection in future, your body knows exactly how to fight it.

The Two Main Types of Vaccines

Vaccines come in a few forms, but they generally fall into two main categories:

1. Live Attenuated Vaccines

These contain a weakened version of a live virus or bacteria. It’s strong enough to trigger an immune response but not strong enough to cause serious illness in healthy people.

Examples include:

• MMR (measles, mumps and rubella)

• Yellow fever vaccine

• Chickenpox (varicella) vaccine

Pros:
✅ Mimics natural infection
✅ Produces strong and lasting immunity (often with fewer doses)

Cons:
❌ Not suitable for people with weakened immune systems
❌ Can (rarely) cause a mild form of the illness as a side effect
❌ Requires careful storage (often needs refrigeration)

2. Inactivated Vaccines

These are made from killed or inactive forms of the virus or bacteria, or fragments of the pathogen like proteins or sugars.

Examples include:

• Hepatitis A

• Polio (inactivated form)

• Rabies

• Typhoid (injection)

Pros:
✅ Cannot cause disease
✅ Safe for immunocompromised individuals
✅ More stable than live vaccines

Cons:
❌ Weaker immune response compared to live vaccines
❌ Often requires multiple doses or boosters
❌ Some forms (like polysaccharide vaccines) don’t work well in young children unless modified

What About mRNA and DNA Vaccines?

You might’ve heard about mRNA vaccines during the COVID-19 pandemic. These are part of a new generation of vaccines that use your body’s own cells to make a harmless piece of the virus—called an antigen—which then triggers your immune system to respond.

• mRNA vaccines (e.g., Pfizer-BioNTech COVID-19 vaccine) deliver instructions to your cells to produce the antigen.

• DNA vaccines use similar principles but require different delivery methods.

These innovative vaccines are safe, effective, and allow for rapid development during outbreaks.

What Are Conjugate Vaccines?

Some inactivated vaccines—like the pneumococcal vaccine—are polysaccharide vaccines, made from sugar-like molecules on the surface of bacteria. On their own, these don’t work well in young children.

So scientists have developed conjugate vaccines, which attach the polysaccharide to a protein to boost the immune response. These work much better in children and can trigger long-term protection.

Summary Table: Live vs Inactivated Vaccines

Vaccines Are Safe, Effective and Life-Saving

Understanding how vaccines work helps us appreciate just how important they are—not only for individual protection, but for public health too. Whether you're getting childhood jabs, planning international travel, or catching up on adult boosters, we're here to help.

If you're unsure about your vaccine needs, book a consultation at Ready Health Clinic. Our team of experienced medical professionals can guide you through your options.

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