[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Immunology](https://durgical.com/en/immunology/) › [Vaccines](https://durgical.com/en/immunology/#a-vaccines) › Vaccine types: live, inactivated, subunit, toxoid, mRNA, vector

[Immunology](https://durgical.com/en/immunology/) · [Vaccines](https://durgical.com/en/immunology/#a-vaccines)

# 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

## Key points

- Live = humoral and cellular, long-lasting; contraindicated in severe immunodeficiency and pregnancy.
- Inactivated = safe in immunosuppressed people, mostly antibodies, needs boosters.
- Plain polysaccharide: T-independent response, poor before age 2; conjugation makes it T-dependent.
- Toxoid: tetanus and diphtheria; protects against the toxin.
- BCG, MMR, varicella, yellow fever, rotavirus and oral polio are live.

## 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) |

## Memory aid

A live vaccine needs a host who can fight back: never in a severely immunosuppressed person, never in pregnancy.

## 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.

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## Related

- [Live vaccines: who should not receive them](https://durgical.com/en/immunology/live-vaccines-who-should-not-receive-them/)
- [Colombia's PAI schedule (which vaccines, at what age)](https://durgical.com/en/immunology/colombia-s-pai-schedule/)
- [The cold chain](https://durgical.com/en/immunology/the-cold-chain/)
- [Passive immunization: immunoglobulins and antitoxins](https://durgical.com/en/immunology/passive-immunization-immunoglobulins-and-antitoxins/)
- [Herd immunity and outbreak control](https://durgical.com/en/immunology/herd-immunity-and-outbreak-control/)
- [Primary vs secondary response and memory](https://durgical.com/en/immunology/primary-vs-secondary-response-and-memory/)
- [B-cell activation, class switching and affinity maturation](https://durgical.com/en/immunology/b-cell-activation-class-switching-and-affinity-maturation/)
- [T-cell activation: two signals and superantigens](https://durgical.com/en/immunology/t-cell-activation-two-signals-and-superantigens/)

## Microorganisms

- [Measles virus](https://durgical.com/en/microbiology/measles-virus/)
- [Rubella virus](https://durgical.com/en/microbiology/rubella-virus/)
- [Mumps virus](https://durgical.com/en/microbiology/mumps-virus/)
- [Varicella-zoster virus](https://durgical.com/en/microbiology/varicella-zoster-virus/)
- [Yellow fever virus](https://durgical.com/en/microbiology/yellow-fever-virus/)
- [Rotavirus](https://durgical.com/en/microbiology/rotavirus/)
- [Mycobacterium tuberculosis](https://durgical.com/en/microbiology/mycobacterium-tuberculosis/)
- [Hepatitis B virus](https://durgical.com/en/microbiology/hepatitis-b-virus/)
- [Human papillomavirus](https://durgical.com/en/microbiology/human-papillomavirus/)
- [Haemophilus influenzae](https://durgical.com/en/microbiology/haemophilus-influenzae/)
- [Streptococcus pneumoniae](https://durgical.com/en/microbiology/streptococcus-pneumoniae/)
- [Clostridium tetani](https://durgical.com/en/microbiology/clostridium-tetani/)
- [Corynebacterium diphtheriae](https://durgical.com/en/microbiology/corynebacterium-diphtheriae/)
- [SARS-CoV-2](https://durgical.com/en/microbiology/sars-cov-2/)

[← All of immunology](https://durgical.com/en/immunology/)

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](https://www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-1-principles-of-vaccination.html) (Centers for Disease Control and Prevention (CDC), 2021); [The different types of COVID-19 vaccines](https://www.who.int/news-room/feature-stories/detail/the-race-for-a-covid-19-vaccine-explained) (World Health Organization, 2021); [¿Cómo funcionan las vacunas?](https://vacunacion.minsalud.gov.co/Vacunas/Paginas/como-funcionan-las-vacunas.aspx) (Ministerio de Salud y Protección Social de Colombia, 2026); [Vaccines and immunization: What is vaccination?](https://www.who.int/news-room/questions-and-answers/item/vaccines-and-immunization-what-is-vaccination) (World Health Organization, 2021).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/immunology/vaccine-types-live-inactivated-subunit-toxoid-mrna-vector/