Clinical Images
Immunization Schedules
The board does not ask you to recite every acronym. It asks whether you know when, which type, and when not to.
Pathophysiology
How Vaccines Build Immunity
Cause → effect: what you inject → what the immune system remembers → what disease you prevent.
Active vs passive immunity
Active immunity → antigen exposure → B cells make antibodies + memory cells → protection lasts years to life. That is what routine vaccines do.
Passive immunity → ready-made antibody (HBIG, varicella zoster immune globulin, rabies immune globulin) → immediate protection → wanes in weeks to months. Use when the patient cannot mount a fast enough response (perinatal HBV exposure, rabies PEP, VZV exposure in high-risk contacts).
Board chain: live vaccine → replicates a little → strong cellular + humoral memory. Killed/subunit vaccine → no replication → often needs more doses and boosters to reach the same memory depth.
Vaccine Types
Know the Weapon Class
Tap each card. Live vs killed is the single biggest contraindication fork in clinical practice.
Live attenuated
- Examples: MMR, varicella, rotavirus, LAIV (intranasal flu), yellow fever
- Effect: cellular + humoral immunity; usually 1-2 doses for life
- Contraindicated: pregnancy, severe immunocompromise, recent blood products (varies)
- Board trap: rotavirus is LIVE oral, not killed
Inactivated
- Examples: IPV (polio), inactivated flu shot, Hep A, Hep B, rabies
- Effect: humoral immunity; multiple doses needed
- Safer in: immunocompromised hosts, pregnancy (most killed vaccines OK)
- Board trap: IPV at 2, 4, 6-18 mo, 4-6 yr; never OPV in US
Toxoid
- Examples: tetanus (T), diphtheria (D) in DTaP/Tdap/Td
- Effect: neutralizing antibodies against toxin, not the bacteria
- Board trap: encephalopathy within 7 days of prior DTaP = contraindication to future pertussis containing vaccines, not tetanus
Conjugate
- Examples: Hib (PRP-T), PCV13/15/20, MenACWY, MenB
- Why conjugate: plain polysaccharide vaccines fail in infants <2 yr (T-independent response)
- Effect: T-cell help → memory in babies
- Board trap: asplenia/sickle cell needs conjugate + polysaccharide pneumococcal series
Presentation
Routine Birth to 18 Months
The visit ages the clinical medicine love: 2, 4, 6, 12-15, and 4-6 years.
| Age | Routine vaccines (high yield) | Why this visit matters |
|---|---|---|
| Birth | Hep B #1 (within 24 h) | Perinatal HBV protocol if mom HBsAg+ (vaccine + HBIG within 12 h) |
| 2 mo | DTaP, IPV, Hib, PCV, RV #1, Hep B #2 | Starts the primary series; rotavirus window opens (must finish by 8 mo) |
| 4 mo | DTaP, IPV, Hib, PCV, RV #2 | Second priming dose; spacing builds affinity maturation |
| 6 mo | DTaP, Hib, PCV, RV #3 (if 3-dose series), Hep B #3, annual flu | Flu season: first flu season needs 2 doses if <9 yr and never vaccinated before |
| 12-15 mo | MMR, varicella, Hep A #1, Hib booster, PCV booster, DTaP #4 | Live vaccines OK if not immunocompromised; separates infant from toddler immunity |
| 4-6 yr | DTaP #5, IPV #4, MMR #2, varicella #2 | School entry boosters; second MMR/varicella before kindergarten |
Presentation clues that map back to the schedule
- Whooping cough in a 2-month-old: too young for full immunity → cocoon with Tdap in pregnancy (27-36 wk) and household contacts.
- Measles in an unvaccinated 10-month-old: first MMR usually at 12 mo → early dose only for outbreak/travel (does not count toward routine 2-dose series if given <12 mo).
- Rotavirus diarrhea in a 9-month-old who never got RV: too old to start series (must complete by 8 mo; first dose by 15 wk).
- Hep B in a teen with no records: catch-up series (0, 1-2 mo, 4-6 mo) regardless of age.
Diagnosis
Screen Before You Stick
Contraindication = do not give. Precaution = can give if benefit outweighs risk; clinical medicine test the difference.
True contraindication: anaphylaxis to prior dose or vaccine component
Prior life-threatening allergic reaction to the vaccine or a known component (gelatin, neomycin, egg protein in yellow fever only) → do not repeat that vaccine.
Egg allergy alone is NOT a contraindication to egg-cultured inactivated flu vaccine in 2024+ guidelines.
DTaP-specific: encephalopathy within 7 days of prior dose
Encephalopathy (not simple febrile seizure) within 7 days of prior DTaP → contraindication to future pertussis-containing vaccines. Give Td/Tdap without pertussis? Use Td for tetanus boosters; Tdap once in adolescence/adult if pertussis contraindication absent later.
Febrile seizure after DTaP is a precaution, not a contraindication.
Live vaccines: pregnancy and severe immunocompromise
MMR, varicella, rotavirus, LAIV → contraindicated in pregnancy and severe T-cell immunodeficiency (SCID, active chemotherapy, high-dose steroids).
HIV with CD4% appropriate for age: MMR and varicella ARE indicated. Mild HIV is not an automatic live-vaccine ban.
Precaution: moderate/severe acute illness
Fever with moderate/severe illness → defer until recovered. Minor illness (otitis, low-grade fever) → vaccinate.
clinical medicine love "child with otitis media at well visit" → still vaccinate today.
Management
Special Populations & Catch-Up
High-yield management rules
- Preterm infant, medically stable: vaccinate at chronological age, same doses as term infant. Do not wait for corrected age.
- Asplenia / sickle cell: PCV series + PPSV23 + MenACWY + MenB + annual flu; penicillin prophylaxis until at least age 5.
- Household contact of immunocompromised patient: all close contacts should be fully immunized; live vaccines for healthy siblings are generally OK (rotavirus shedding is a theoretical risk, discuss with oncology team).
- Catch-up: minimum intervals matter more than restarting series; MMR #2 at least 4 weeks after #1; no maximum interval between doses.
- Tdap in pregnancy: every pregnancy, 27-36 weeks, to protect newborn via transplacental IgG before first infant DTaP at 2 months.