TYPE
HOW IT WORKS
EXAMPLES
CAUTIONS
Weakened organism replicates → MHC I and II presentation → CD8⁺ + CD4⁺ + antibodies
MMR, varicella, yellow fever, rotavirus, intranasal flu, oral typhoid, BCG, oral polio
Not in pregnancy, SCID, high-dose steroids, chemotherapy · can revert (OPV)
Whole organism killed → antibodies mainly
IPV (Salk), hepatitis A, rabies, injected influenza, Japanese encephalitis
Safe when immunocompromised; boosters
Purified or recombinant proteins
HBV (HBsAg), HPV (L1 VLPs), recombinant zoster, acellular pertussis
Adjuvants boost response
Inactivated toxin → neutralizing antitoxin antibodies
Tetanus, diphtheria
Boost every 10 years; no protection against colonization
T-independent B-cell response; no memory, weak under age 2
PPSV23, typhoid Vi
Poor in infants
Polysaccharide linked to carrier protein → helper T cells → class switching, memory
Hib, PCV15/20, MenACWY
Effective in infants
Host cells make antigen → antibodies + T cells
SARS-CoV-2, some RSV; Ebola (rVSV vector)
Myocarditis rare (young men, mRNA)
Preformed antibodies; immediate, short-lived, no memory
Rabies IG, HBIG, tetanus IG, VZIG, IVIG, nirsevimab (RSV), antitoxins (botulism)
Given with active vaccine after exposure
Encapsulated organisms
Pneumococcal, Hib, meningococcal (ACWY + B)
≥ 2 weeks before elective splenectomy
Protect mother and infant
Tdap (27–36 weeks each pregnancy), inactivated influenza, RSV (32–36 weeks), COVID
No MMR, varicella, live flu
Exposure-based
HBV (healthcare), rabies pre-exposure, yellow fever, typhoid, Japanese encephalitis
Yellow fever is live
Residual proteins
Influenza okay with egg allergy; yellow fever contains egg
Gelatin, neomycin in MMR/varicella
Not true contraindications
—
Mild illness, low-grade fever, antibiotics, breastfeeding, family member pregnant
Vaccinate anyway