---

📚 Pediatric Infections & Immunization — Study Notes

---

PART 1: IMMUNIZATION

1.1 Principles of Active Immunization

• Immunogenicity depends on vaccine type, adjuvants, route, and host immune status.
• Vaccines contain: live attenuated organisms, inactivated organisms, toxoids, subunit/protein antigens, polysaccharide conjugates, or mRNA.
• Adjuvants (e.g., aluminum salts, AS04) enhance the immune response by increasing antigen presentation.
• Herd immunity: When a sufficient proportion of the population is immune, transmission is interrupted, protecting unimmunized individuals. Thresholds vary by pathogen (measles requires ~95% coverage).

---

1.2 Childhood Immunization Schedule (USA — AAP/CDC)

Key principle: Vaccines should be given at the earliest recommended age for maximum protection. Interrupted series do NOT need to be restarted.

---

1.3 Vaccine Types & Examples

---

1.4 Special Immunization Circumstances

• Avoid all live vaccines (MMR, Varicella, LAIV, Rotavirus).
• May still receive inactivated vaccines, though immune response may be blunted.
• Exception: HIV-infected children with CD4 ≥ 15% (and age-specific thresholds) may receive MMR and Varicella.

---

1.5 Passive Immunization

Key rule: Live vaccines (MMR, Varicella) must be delayed ≥3–11 months after IGIV (depending on dose) because passively acquired antibodies can inhibit active immune response.

---

1.6 Vaccine Safety

• Local (redness, swelling, pain at injection site): most common; self-limited.
• Systemic (fever, irritability): especially DTaP, MMR.
• Febrile seizures: occur 6–14 days post-MMR or after combined MMRV; not associated with long-term sequelae.

• Intussusception: previously associated with RotaShield (withdrawn); current vaccines (RotaTeq, Rotarix) carry a very small risk (~1–2 extra cases per 100,000 first doses).
• Anaphylaxis: rare; epinephrine (1:1,000) 0.01 mg/kg IM is treatment. All vaccine providers must be equipped to manage.
• Vaccine-strain viral infection: VAPP (vaccine-associated paralytic polio) with OPV — now OPV is not used in the USA.

• Contraindication = condition making vaccine likely to cause serious adverse reaction (e.g., severe allergic reaction to prior dose → do not give again).
• Precaution = condition that might increase risk but vaccination may still be appropriate (e.g., moderate/severe acute illness → defer until resolved).

---

PART 2: COMMON PEDIATRIC INFECTIOUS DISEASES

2.1 Pertussis (Whooping Cough)

• NP swab/wash for PCR (preferred; most sensitive in first 3 weeks)
• Culture (gold standard historically; decreasing use)
• Serology: elevated IgG anti-pertussis toxin (2–8 weeks after cough onset)
• Classic lab finding: marked lymphocytosis (WBC 20,000–100,000+ cells/µL)

• Azithromycin (preferred for infants < 1 month): 10 mg/kg/day × 5 days
• Azithromycin or clarithromycin: for children ≥ 1 month
• TMP-SMX: alternative for those intolerant to macrolides (avoid in < 2 months)
• Antimicrobials shorten the contagious period if given in the catarrhal stage; limited effect on clinical course once in the paroxysmal stage.

• DTaP × 5 doses (2, 4, 6, 15–18 months, 4–6 years)
• Tdap at 11–12 years and every pregnancy (27–36 weeks)
• Post-exposure prophylaxis: azithromycin for close household contacts regardless of vaccination status

Waning immunity from acellular vaccine is the main reason for increased pertussis in school-age children and adolescents.

---

2.2 Measles (Rubeola)

• Prodrome: 3 Cs — Cough, Coryza, Conjunctivitis + fever (3–4 days)
• Koplik spots: pathognomonic bluish-white spots on buccal mucosa; appear 1–2 days before rash
• Rash: morbilliform (maculopapular), starts behind ears → face → trunk → extremities; lasts ~5 days
• Fever may reach 40°C

• Otitis media (most common)
• Pneumonia (viral, bacterial superinfection)
• Encephalitis (1:1,000 cases) — most dangerous acute complication
• Subacute sclerosing panencephalitis (SSPE): rare, fatal, occurs 7–10 years post-infection; characterized by progressive neurological deterioration

• MMR #1 at 12–15 months; MMR #2 at 4–6 years
• Post-exposure prophylaxis: MMR within 72 hours (susceptible contacts) OR IGIM/IGIV within 6 days (immunocompromised, infants < 6 months, pregnant women)
• Herd immunity threshold: ~95% vaccination coverage

---

2.3 Varicella-Zoster Virus (VZV)

• Prodrome 1–2 days: fever, malaise
• Rash: pruritic, vesicles on erythematous base ("dewdrop on a rose petal"), appears in crops; all stages simultaneously (macule → papule → vesicle → pustule → crust)
• Distribution: centripetal (starts on trunk/face, spreads to extremities)

• Bacterial superinfection (most common; Group A Strep, S. aureus)
• Pneumonia (especially in adults, immunocompromised)
• Cerebellar ataxia
• Encephalitis
• Reye syndrome if aspirin given → avoid aspirin in varicella!

• Healthy children: supportive (antihistamines, acetaminophen — NOT aspirin)
• Acyclovir indicated for: immunocompromised, adolescents (>12 y), adults, secondary household cases, chronic pulmonary/skin disease, newborns exposed perinatally
• IV acyclovir: immunocompromised, neonatal, or disseminated disease

• Varicella vaccine × 2 doses: 12–15 months and 4–6 years
• Post-exposure: Vaccine within 3–5 days OR VariZIG within 10 days (immunocompromised, pregnant, neonates of VZV-susceptible mothers)

---

2.4 Haemophilus influenzae type b (Hib)

• Before vaccine: leading cause of bacterial meningitis in children < 5 years
• After Hib conjugate vaccine: dramatic reduction > 99% in invasive disease
• Conjugate vaccine converts T-independent → T-dependent response → immunologic memory even in infants < 2 years

---

2.5 Streptococcus pneumoniae (Pneumococcus)

• PCV13 (13-valent conjugate): 4 doses at 2, 4, 6, 12–15 months for all infants
• PPSV23 (23-valent polysaccharide): for high-risk children ≥2 years, ≥8 weeks after last PCV13
• PCV15 / PCV20 (newer formulations): now preferred by ACIP for adults

Key rule: MenACWY-D (Menactra) should not be given within 4 weeks of PCV13 due to immune interference.

---

2.6 Neisseria meningitidis (Meningococcal Disease)

• Fever + petechial/purpuric rash = meningococcemia (non-blanching!) → septic shock
• Waterhouse-Friderichsen syndrome: bilateral adrenal hemorrhage → adrenal insufficiency in overwhelming meningococcemia

• MenACWY (conjugate): 11–12 years + booster at 16 years; earlier for high-risk groups
• MenB (Bexsero or Trumenba): 16–23 years (Category B recommendation); recommended for high-risk (asplenia, complement deficiency, outbreak)

---

2.7 Group B Streptococcus (GBS) — Neonatal

• Universal maternal screening at 35–37 weeks gestation
• Intrapartum antibiotic prophylaxis (IAP) with IV penicillin G (or ampicillin) if:
  • GBS positive culture, or
  • GBS bacteriuria in this pregnancy, or
  • Prior infant with invasive GBS disease, or
  • GBS status unknown + risk factors (< 37 weeks, prolonged ROM ≥18 h, intrapartum fever ≥38°C)

---

2.8 Respiratory Syncytial Virus (RSV)

• Most common cause of bronchiolitis in infants (< 2 years)
• Leading cause of hospitalization in infants < 1 year

• Upper respiratory illness → wheezing, hyperinflation, atelectasis, tachypnea, use of accessory muscles
• Apnea, especially in premature infants

• Palivizumab (anti-RSV monoclonal antibody): monthly IM injections October–March
  • Indicated for: prematurity ≤28 weeks (up to 12 months), ≤32 weeks + CLD or CHD, ≤35 weeks with risk factors
• Nirsevimab (longer-acting monoclonal): single dose; now preferred (AAP 2023)
• RSV maternal vaccine (Abrysvo): given 32–36 weeks gestation to protect infants 0–6 months

---

2.9 Rotavirus

• #1 cause of severe diarrhea in children worldwide (< 5 years)
• Fecal-oral transmission; incubation 1–3 days

• RotaTeq (RV5): 3 doses at 2, 4, 6 months
• Rotarix (RV1): 2 doses at 2, 4 months
• First dose must be given before 15 weeks of age; series must be completed by 8 months
• Small increased risk of intussusception (~1–2/100,000 first doses)

---

2.10 Diphtheria

• Pseudomembrane: tough, grey membrane on pharynx/tonsils — bleeds on removal
• Toxin → myocarditis (arrhythmias, heart block) and neuropathy (palatal palsy, oculomotor palsy, Guillain-Barré-like peripheral neuropathy)
• "Bull neck" from cervical lymphadenopathy

---

2.11 Tetanus

• Trismus (lockjaw): hallmark
• Risus sardonicus: spastic facial muscle contraction
• Opisthotonus: arching of back
• Autonomic instability: diaphoresis, labile BP, tachycardia
• Neonatal tetanus: rigidity and spasms in newborn; occurs from unclean cord care.

---

2.12 Hepatitis A & B

• Fecal-oral transmission; self-limited; no chronic state
• Vaccine: 2-dose series at 12–23 months (HepA)
• Post-exposure: vaccine within 2 weeks (healthy, 1–40 y) or IGIM for < 1 year, immunocompromised, or > 40 years

• Parenteral/sexual/vertical (perinatal) transmission; can cause chronic infection → cirrhosis/HCC
• Perinatal: Neonate of HBsAg+ mother → HepB vaccine + HBIG within 12 hours of birth
• Vaccine: 3-dose series (birth, 1–2 months, 6–18 months)
• Serologic markers:
  • HBsAg: current infection
  • Anti-HBs: immunity (vaccine or resolved infection)
  • Anti-HBc IgM: acute infection
  • HBeAg: high viral replication/infectivity

---

2.13 HIV in Children

• Maternal ART throughout pregnancy
• IV zidovudine during labor/delivery
• Neonatal prophylaxis (ZDV ± nevirapine based on maternal viral load)
• C-section if maternal VL > 1,000 copies/mL at 36 weeks
• Avoid breastfeeding (in resource-rich settings)

---

PART 3: INFECTION CONTROL IN PEDIATRIC SETTINGS

3.1 Transmission-Based Precautions

Hand hygiene is the single most important measure for preventing healthcare-associated infections.

3.2 Infection Control in Child Care Settings

• Diarrheal illness is better controlled by infection control measures than respiratory illness in group settings.
• Exclusion criteria for diarrhea: stool not containable in diaper/toilet, or stool frequency > 2 above baseline.
• Immunization is the most effective intervention for reducing respiratory illness (influenza, pertussis, varicella) in group childcare.

---

PART 4: ANTIMICROBIAL THERAPY IN PEDIATRICS

4.1 Key Antibiotic Classes & Pediatric Notes

4.2 Antimicrobial Prophylaxis Indications

• Surgical prophylaxis: administer within 60 minutes pre-incision; discontinue within 24 hours post-surgery.
• Neonatal ophthalmia: topical erythromycin ointment at birth prevents gonococcal ophthalmia (legally mandated in most US states).
• Recurrent UTI: TMP-SMX or nitrofurantoin for children with VUR or structural anomalies.
• Rheumatic fever prevention: daily penicillin V or amoxicillin for ≥ 5–10 years after initial episode of rheumatic fever.

---

PART 5: HIGH-YIELD MNEMONICS & TABLES

5.1 Vaccine-Preventable Disease Quick Reference

5.2 Mnemonics

• Measles prodrome: 3 Cs — Cough, Coryza, Conjunctivitis
• Pertussis stages: CPC — Catarrhal → Paroxysmal → Convalescent
• Meningococcemia: Non-blanching rash = Petechiae/purpura → emergency
• Tetanus triad: Trismus + Risus sardonicus + Opisthotonus
• Vaccine contraindications (live): PAIL — Pregnancy, AIDS/immunocompromised, Immunosuppressive therapy, Last dose reaction (severe)

---