Vaccine types: live, inactivated, subunit, toxoid, mRNA, vector !
- Topic
Vaccines teach the immune system to recognize a germ without causing the disease. They carry a weakened germ, a killed one, a piece of it or its instructions.
Updated 2026-11-01
What it is
A vaccine presents antigens from a pathogen to build active immunity and memory without the person going through the infection. By what they contain, vaccines are live attenuated, inactivated whole-organism, subunit (proteins, polysaccharides, conjugates), toxoids, or genetic platforms (mRNA and viral vectors). The type sets how strong the response is, how many shots are needed and who can receive it.
Key facts
- Live attenuated vaccines replicate in the body and usually give lasting humoral and cellular immunity, close to natural infection.
- Inactivated vaccines cannot replicate: they are safe in immunosuppressed people, but mostly induce antibodies and often need boosters.
- Plain polysaccharides activate B cells without T-cell help, so children under 2 respond poorly; conjugating them to a protein makes the response T-dependent.
- Toxoids are inactivated bacterial toxins (tetanus, diphtheria): they protect against the toxin, not against colonization.
- Adjuvants such as aluminium salts boost the response to non-live vaccines.
Vaccine types, with strengths and limits
| Type | Examples | Pros | Cons | Live? |
|---|---|---|---|---|
| Live attenuated | MMR (measles, rubella, mumps), varicella, yellow fever, rotavirus, BCG, oral polio | Strong, lasting humoral and cellular response; few shots | Contraindicated in severe immunodeficiency and pregnancy; heat- and light-sensitive; received antibodies can block it | Yes |
| Inactivated (whole organism) | Inactivated polio, hepatitis A, rabies, inactivated influenza | Cannot cause the disease; safe in immunosuppressed people | Weaker, mostly antibody response; needs several shots and boosters | No |
| Subunit or recombinant | Hepatitis B, HPV, acellular pertussis | Very safe; defined antigen | Usually needs an adjuvant and boosters | No |
| Polysaccharide conjugate | Haemophilus influenzae type b, pneumococcal conjugate, meningococcal conjugate | Works in infants and builds memory by making the response T-dependent | Covers only the serotypes included | No |
| Toxoid | Tetanus, diphtheria | Protects against the toxin that does the damage | Needs periodic boosters | No |
| mRNA | COVID-19 | Fast to develop and update; humoral and cellular response | Recent platform; needs a strict cold chain | No |
| Viral vector | Ebola, some COVID-19 vaccines | Strong cellular response; fast to develop | Prior immunity to the vector can blunt it | No (non-replicating vector in most) |
Test yourself
Think of the answer, then tap the question to see it.
Why does a plain polysaccharide vaccine protect a 6-month-old infant poorly?
Polysaccharides activate B cells without T-cell help, a pathway that is immature before age 2; conjugating them to a protein makes the response T-dependent and builds memory.
What type of vaccine are the tetanus and diphtheria vaccines?
Toxoids: inactivated bacterial toxins that induce neutralizing antibodies against the toxin.
What immunological advantage do live attenuated vaccines have over inactivated ones?
They replicate and induce lasting humoral and cellular immunity, much like natural infection, with fewer shots.
Which childhood vaccines are live attenuated?
BCG, rotavirus, MMR (measles, rubella, mumps), varicella, yellow fever, and oral polio where it is used.
Related
- Live vaccines: who should not receive them
- Colombia's PAI schedule (which vaccines, at what age)
- The cold chain
- Passive immunization: immunoglobulins and antitoxins
- Herd immunity and outbreak control
- Primary vs secondary response and memory
- B-cell activation, class switching and affinity maturation
- T-cell activation: two signals and superantigens
Microorganisms
- Measles virus
- Rubella virus
- Mumps virus
- Varicella-zoster virus
- Yellow fever virus
- Rotavirus
- Mycobacterium tuberculosis
- Hepatitis B virus
- Human papillomavirus
- Haemophilus influenzae
- Streptococcus pneumoniae
- Clostridium tetani
- Corynebacterium diphtheriae
- SARS-CoV-2
Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.
Sources: Chapter 1: Principles of Vaccination | Pink Book | CDC (Centers for Disease Control and Prevention (CDC), 2021); The different types of COVID-19 vaccines (World Health Organization, 2021); ¿Cómo funcionan las vacunas? (Ministerio de Salud y Protección Social de Colombia, 2026); Vaccines and immunization: What is vaccination? (World Health Organization, 2021).
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Representative model, for educational purposes only.