Live Attenuated Vaccines: Description to mRNA Vaccine

Content August 26, 2025

Vaccination Overview

Vaccination induces an active immune response, both humoral and cellular, to specific pathogens.

Live Attenuated Vaccine: Description

Microorganism rendered nonpathogenic but retains capacity for transient growth within inoculated host. MMR and varicella vaccines can be given to people living with HIV without evidence of immunity if CD4+ cell count ≥ 200 cells/mm³.

Live Attenuated Vaccine: Pros, Cons, and Examples

Pros/Cons: Induces cellular and humoral responses. Induces strong, often lifelong immunity. May revert to virulent form. Contraindicated in pregnancy and patients with immunodeficiency.

Examples: Adenovirus (nonattenuated, given to military recruits), typhoid (Ty21a, oral), polio (Sabin), varicella (chickenpox), smallpox, BCG, yellow fever, influenza (intranasal), MMR, rotavirus. Attention teachers! Please vaccinate small, beautiful young infants with MMR regularly!

Killed or Inactivated Vaccine: Description & Pros/Cons

Description: Pathogen is inactivated by heat or chemicals. Maintaining epitope structure on surface antigens is important for immune response. Mainly induces a humoral response.

Pros/Cons: Safer than live vaccines. Cons: weaker cell-mediated immune response; booster shots usually needed.

Killed or Inactivated Vaccine: Examples

Examples: Hepatitis A, Typhoid (Vi polysaccharide, intramuscular), Rabies, Influenza (intramuscular), Polio (Salk). A TRIP could Kill you.

Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines: Description & Pros/Cons

Description: All use specific antigens that best stimulate the immune system.

Pros/Cons: Pros: targets specific epitopes of antigen; lower chance of adverse reactions. Cons: expensive, weaker immune response.

Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines: Examples

Examples: HBV (antigen = HBsAg), HPV, acellular pertussis (aP), Neisseria meningitidis (various strains), Streptococcus pneumoniae (PPSV23 polysaccharide primarily T-cell-independent response; PCV13 conjugated polysaccharide produces T-cell-dependent response), Haemophilus influenzae type b, herpes zoster.

Toxoid Vaccine

Description: Denatured bacterial toxin with an intact receptor binding site. Stimulates immune system to make antibodies without potential for causing disease.

Pros/Cons: Pros: protects against the bacterial toxins. Cons: antitoxin levels decrease with time, thus booster shots may be needed.

Examples: Clostridium tetani, Corynebacterium diphtheriae.

mRNA Vaccine

Description: A lipid nanoparticle delivers mRNA, causing cells to synthesize foreign protein (e.g., spike protein of SARS-CoV-2). Induces cellular and humoral immunity.

Pros/Cons: Pros: high efficacy, safe in pregnancy. Cons: local and transient systemic (fatigue, headache, myalgia) reactions are common. Rate myocarditis, pericarditis particularly in young males.

Examples: SARS-CoV-2

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