Viral Vaccines

Vaccination is the most effective tool medicine has for preventing viral disease, and the only one that has ever eradicated a human virus. It is estimated to have saved more than 150 million lives over the past five decades. A vaccine works by showing the immune system part or all of a virus under controlled conditions, so that protective memory is in place before the first natural infection.

Two distinctions organise the whole topic. The first is how the antigen is presented, which defines the vaccine platform and sets the trade-off between how strong the immune response is and how safe the vaccine is to give. The second is how protection is acquired: active immunisation trains the person to make their own durable response, while passive immunisation transfers ready-made antibody for protection that is immediate but temporary. At the population level, high coverage produces herd immunity, which protects even those who cannot be vaccinated. The topic is treated in three articles.

→ See Vaccine Types and Platforms for how vaccines work and the platforms that deliver viral antigen: live attenuated, inactivated, subunit and virus-like particle, viral-vectored, and the nucleic-acid (mRNA and DNA) vaccines, with adjuvants, contraindications and how the seasonal influenza vaccine is made each year.

→ See Vaccination in Practice and Public Health for herd immunity, vaccine failure, safety and adverse-event reporting, schedules and special populations, surveillance, and eradication, with the South African Expanded Programme on Immunisation.

→ See Passive Immunisation and Immunoglobulins for the antibody products (polyclonal immunoglobulins and monoclonal antibodies) used for prophylaxis and treatment, when to use them, and how they interact with active vaccination.

Vaccine platforms at a glance

Platform	What it is	Live?	Examples
Live attenuated	A weakened whole virus that still replicates	Yes	Measles, mumps, rubella, varicella, oral polio, yellow fever, rotavirus
Inactivated	A killed whole virus	No	Inactivated polio, hepatitis A, rabies, influenza
Subunit / recombinant	A purified or engineered viral protein	No	Recombinant influenza, recombinant zoster
Virus-like particle	Self-assembled capsid proteins, no genome	No	Hepatitis B, human papillomavirus
Viral-vectored	A carrier virus delivering the antigen gene	Vector-dependent	Ebola, some COVID-19
mRNA / DNA	The genetic instructions for the antigen	No	COVID-19 (mRNA)

Viral vaccines and passive options

Which human viruses have a licensed vaccine, the platform used, and whether a passive antibody option exists.

Virus	Vaccine type	Passive option
Hepatitis A	Inactivated	Normal human immunoglobulin
Hepatitis B	Recombinant subunit (virus-like particle)	Hepatitis B immunoglobulin
Human papillomavirus	Virus-like particle	None
Influenza	Inactivated, recombinant or live attenuated	None routine
Measles	Live attenuated	Normal human immunoglobulin (post-exposure)
Mumps	Live attenuated	None
Rubella	Live attenuated	None
Varicella-zoster	Live (varicella, zoster); recombinant (zoster)	Varicella-zoster immunoglobulin
Poliovirus	Live oral and inactivated	None
Rotavirus	Live attenuated, oral	None
Yellow fever	Live attenuated (17D)	None
Rabies	Inactivated	Rabies immunoglobulin
SARS-CoV-2	mRNA, viral-vector, protein subunit	Monoclonal antibodies (variable)
Respiratory syncytial virus	Recombinant (maternal and older adult)	Nirsevimab or palivizumab
Mpox and smallpox	Live (vaccinia, modified vaccinia Ankara)	Vaccinia immunoglobulin
Ebola	Live viral-vector	Monoclonal antibodies (treatment)

Key terms

Term	Meaning
Active immunisation	Giving an antigen so the person makes their own lasting, memory-bearing response.
Passive immunisation	Transferring ready-made antibody for immediate but temporary protection, with no memory.
Live versus non-live	A live vaccine replicates (strong, broad immunity, but unsafe in pregnancy and immunocompromise); a non-live vaccine cannot replicate (safe in those groups, usually needs an adjuvant and boosters).
Herd immunity	Protection of the unvaccinated once enough of a population is immune to interrupt transmission; the threshold is about 95% for measles.
Correlate of protection	A measurable immune marker that predicts protection and on which a vaccine can be licensed (a haemagglutination-inhibition titre of about 1:40 for influenza).
Vaccine failure	Failure to respond at all (primary) or waning of an initial response (secondary).
Post-exposure prophylaxis	Vaccine, immunoglobulin or both given after a defined exposure to prevent disease (rabies, hepatitis B, measles, varicella).
Ring vaccination	Vaccinating the contacts around each case, and their contacts, to contain an outbreak; the strategy that helped eradicate smallpox.

References and recommended reading

• Crowe JE Jr. Immunization Against Viral Diseases. In: Fields Virology, 7th edition (Fundamentals), Chapter 15. Wolters Kluwer; 2023. The current comprehensive reference for vaccine immunology and platforms.
• Slifka MK, Amanna IJ. Passive Immunization. In: Plotkin’s Vaccines, 8th edition, Chapter 9. Elsevier; 2023. The reference for passive immunisation.
• Burrell CJ, Howard CR, Murphy FA. Vaccines and Vaccination. In: Fenner and White’s Medical Virology, 5th edition, Chapter 11. Academic Press / Elsevier; 2017. Concise foundational account of vaccine types and principles.
• National Department of Health, South Africa. Expanded Programme on Immunisation (EPI-SA): routine childhood immunisation schedule, 2024 revision.