Introduction
Vaccination is one of the most effective public health interventions, saving millions of lives annually. The CDC childhood immunization schedule is designed to provide protection against 16 vaccine-preventable diseases from birth through adolescence. Herd immunity protects vulnerable populations who cannot be vaccinated.
CDC Immunization Schedule (Birth - 18 Years)
Birth to 15 Months
| Vaccine | Birth | 1 mo | 2 mo | 4 mo | 6 mo | 9 mo | 12 mo | 15 mo |
|---|---|---|---|---|---|---|---|---|
| HepB (Hepatitis B) | D1 | D2 | D3 | |||||
| RV (Rotavirus) | D1 | D2 | D3 (depending on brand) | |||||
| DTaP (Diphtheria, Tetanus, Pertussis) | D1 | D2 | D3 | D4 | ||||
| Hib (H. influenzae type b) | D1 | D2 | D3 (depending on brand) | D4 | ||||
| PCV13/15/20 (Pneumococcal conjugate) | D1 | D2 | D3 | D4 | ||||
| IPV (Inactivated Polio) | D1 | D2 | D3 | |||||
| Influenza (annually) | D1 (starting at 6 months) | |||||||
| MMR (Measles, Mumps, Rubella) | D1 | |||||||
| Varicella (Chickenpox) | D1 | |||||||
| HepA (Hepatitis A) | D1 | D2 (18 mo) |
18 Months to 18 Years
| Vaccine | 18 mo | 4-6 yr | 11-12 yr | 16 yr | 18 yr |
|---|---|---|---|---|---|
| DTaP | D5 | ||||
| DTaP/Tdap | D5 (DTaP) | Tdap | |||
| IPV | D4 | ||||
| MMR | D2 | ||||
| Varicella | D2 | ||||
| HepA | D2 | ||||
| HPV (Gardasil 9) | 2 doses (9-14 yr) or 3 doses (15+ yr) | ||||
| MenACWY (Meningococcal ACWY) | D1 | Booster | |||
| MenB (Meningococcal B) | Optional (shared decision) | ||||
| Influenza | Annually | Annually | Annually | Annually | Annually |
| COVID-19 | See current guidelines | ||||
| RSV (nirsevimab) | Infants <8 months during RSV season; high-risk 8-19 months |
Vaccine Types
| Type | Examples | Mechanism | Advantages | Contraindications |
|---|---|---|---|---|
| Live attenuated (LAIV/MMRV) | MMR, Varicella, LAIV (FluMist), Rotavirus, Zoster (Shingrix is recombinant) | Weakened pathogen replicates without causing disease in immunocompetent | Strong, long-lasting immunity (often 1-2 doses lifelong) | Immunocompromised, pregnancy, severe egg allergy (some) |
| Inactivated/killed | IPV, Hepatitis A, Rabies, Influenza (injectable) | Killed pathogen cannot replicate | Safer for immunocompromised | Generally safe in immunocompromised (may be less immunogenic) |
| Subunit/conjugate | Hib, PCV, MenACWY, Hepatitis B, HPV, DTaP, Tdap | Purified antigens (polysaccharide, protein, toxoid) | Very safe; fewer reactions than whole-cell | Generally none |
| mRNA | COVID-19 (Pfizer, Moderna) | mRNA encoding spike protein delivered in lipid nanoparticle | Rapid development; strong T-cell and antibody response | Only age/medical restrictions |
| Recombinant | HPV (Gardasil 9), Hepatitis B (Engerix-B), Shingrix | Recombinant protein produced in yeast or cells | Highly purified; well-studied | Generally none |
| Viral vector | COVID-19 (J&J), Ebola | Non-replicating viral vector carrying antigen gene | Single-dose often sufficient; stable storage | History of thrombosis with thrombocytopenia (J&J) |
| Toxoid | Tetanus, Diphtheria (Tdap, DTaP) | Inactivated bacterial toxin | Prevents disease caused by toxin | Generally none |
Vaccine-Preventable Diseases
Overview Table
| Disease | Pathogen | Transmission | Key Features in Children | Vaccine Efficacy |
|---|---|---|---|---|
| Hepatitis B | HBV | Blood, bodily fluids, vertical | Can lead to chronic carrier, cirrhosis, HCC | >95% (3 doses) |
| Rotavirus | Rotavirus | Fecal-oral | Severe gastroenteritis, diarrhea, dehydration, hospitalization | 85-98% against severe disease |
| Diphtheria | C. diphtheriae | Respiratory, skin | Pseudomembrane in airway, myocarditis, neuropathy | >95% |
| Tetanus | C. tetani | Soil, wounds | Trismus, rigidity, autonomic instability | Nearly 100% |
| Pertussis | B. pertussis | Respiratory droplets | Paroxysmal cough, whoop, post-tussive emesis; severe in infants | 85-95% (wanes over time) |
| H. influenzae type b | H. influenzae type b | Respiratory droplets | Meningitis, epiglottitis, pneumonia, sepsis | >95% (reduced disease by 99%) |
| Polio | Poliovirus | Fecal-oral | Paralysis (flaccid, asymmetric, lower > upper); 1% of infections | >99% (4 doses) |
| Pneumococcal | S. pneumoniae | Respiratory droplets | Pneumonia, meningitis, bacteremia, otitis media | 75-97% (IPD) |
| Measles | Measles virus | Airborne | Fever, coryza, conjunctivitis, Koplik spots, maculopapular rash; pneumonia, encephalitis, SSPE | 93% (1 dose); 97% (2 doses) |
| Mumps | Mumps virus | Respiratory droplets | Parotitis, orchitis, meningitis, encephalitis; deafness | 88% (2 doses) |
| Rubella | Rubella virus | Respiratory droplets | Mild fever, rash, lymphadenopathy; congenital rubella syndrome (CRS) | >95% |
| Varicella | VZV | Respiratory, contact | Generalized vesicular rash, pneumonia, encephalitis, zoster later | 85-90% (1 dose); >95% (2 doses) |
| Hepatitis A | HAV | Fecal-oral | Jaundice, vomiting, liver failure (rare in children <6) | 85-100% after 2 doses |
| HPV | HPV types 6,11,16,18,31,33,45,52,58 | Sexual contact | Genital warts, cervical/vulvar/penile/anal cancer | >90% (HPV-related cancers) |
| Meningococcal | N. meningitidis | Respiratory droplets | Meningococcemia, meningitis, sepsis; rapid progression | 80-85% (ACWY); 60-90% (B) |
| Influenza | Influenza A/B | Respiratory droplets | Fever, myalgia, cough; pneumonia, myositis, encephalopathy; hospitalization | 40-60% (varies by season) |
Vaccine Safety
Common Reactions
| Reaction | Frequency | Onset | Duration | Management |
|---|---|---|---|---|
| Local pain, redness, swelling | 20-50% | 0-48 hours | 1-3 days | Cold compress, acetaminophen/ibuprofen |
| Fever (mild, <102F) | 5-20% | 12-24 hours | 1-2 days | Acetaminophen/ibuprofen; DO NOT give prophylactically |
| Fussiness/irritability | 20-40% | 12-24 hours | 1-2 days | Comfort measures |
| Decreased appetite | 10-20% | 12-24 hours | 1-2 days | Offer fluids |
| Fatigue/sleepiness | 10-20% | 12-24 hours | 1-2 days | Allow rest |
| Maculopapular rash (MMR/Varicella) | 5-10% | 7-14 days | 2-3 days | Reassurance; not contagious |
Serious Adverse Events (Rare)
| Event | Vaccine | Incidence | Timing |
|---|---|---|---|
| Anaphylaxis | Multiple | 1 in 1,000,000 | 0-30 minutes |
| Febrile seizure | MMRV (first dose) | 1 in 2,500 (higher with MMRV than separate MMR+Varicella) | 5-12 days |
| Intussusception (bowel blockage) | Rotavirus | 1 in 20,000-100,000 | 1-7 days after dose 1-2 |
| Encephalopathy | DTaP (rare; whole-cell DTP higher) | <1 in 1,000,000 | 0-7 days |
| Guillain-Barre syndrome | Influenza | 1-2 per 1,000,000 | 1-6 weeks |
| Thrombosis with thrombocytopenia | COVID-19 (J&J adenovirus vector) | 3-5 per 1,000,000 (women 30-49) | 4-28 days |
| Hypotonic-hyporesponsive episode | DTaP (DTP higher risk) | <1 in 10,000 | 0-48 hours |
Contraindications vs Precautions
| Category | Description | Examples |
|---|---|---|
| True contraindication | DO NOT administer vaccine | Anaphylaxis to prior dose or component; encephalopathy within 7 days of pertussis vaccine |
| Precaution | May defer or proceed with caution (weigh risk/benefit) | Moderate-severe acute illness (with or without fever); recent blood product (for live vaccines); Guillain-Barre within 6 weeks of prior influenza vaccine |
| NOT contraindicated | Can vaccinate | Mild illness, low-grade fever, antibiotic use, breastfeeding, egg allergy (for influenza, except anaphylaxis), family history of seizures, prematurity |
Vaccine Safety Monitoring Systems
| System | Description | Purpose |
|---|---|---|
| VAERS (Vaccine Adverse Event Reporting System) | Passive reporting system (anyone can report) | Identify novel or rare adverse events; detects signals |
| VSD (Vaccine Safety Datalink) | Active surveillance using electronic health records from 10+ managed care organizations | Conducts studies on vaccine safety associations |
| CISA (Clinical Immunization Safety Assessment) | Clinical network of vaccine safety experts | Evaluates complex vaccine safety cases |
| PRISM (Post-Licensure Rapid Immunization Safety Monitoring) | Active surveillance using large health plan data | Rapid monitoring of newly licensed vaccines |
Herd Immunity (Community Immunity)
Concept
| Term | Definition |
|---|---|
| Herd immunity threshold | Percentage of population immune to prevent sustained transmission (1 - 1/R0) |
| R0 (Basic reproduction number) | Number of secondary cases from one infected individual in fully susceptible population |
| Effective R (Rt) | R0 x proportion susceptible; must be <1 for herd immunity |
Thresholds by Disease
| Disease | R0 | Herd Immunity Threshold | Vaccine Coverage Needed |
|---|---|---|---|
| Measles | 12-18 | 92-95% | >95% (2 doses) |
| Pertussis | 12-17 | 92-94% | >94% |
| Polio | 5-7 | 80-86% | >86% |
| Diphtheria | 6-7 | 83-86% | >85% |
| Rubella | 5-7 | 80-85% | >85% |
| Mumps | 4-7 | 75-86% | >86% |
| Smallpox | 5-7 | 80-85% | Eradicated |
| COVID-19 (original) | 3-5 | 60-80% | 70-80% |
| Influenza | 1.5-2 | 30-50% | >50% |
Consequences of Reduced Vaccination
| Outcome | Impact |
|---|---|
| Outbreak of vaccine-preventable disease | Measles outbreaks in undervaccinated communities (e.g., 2014-2015 Disneyland outbreak, 2019 NY outbreaks) |
| Loss of herd immunity | Requires high coverage; pockets of unvaccinated individuals enable outbreaks |
| Vulnerable populations affected | Infants too young to vaccinate, immunocompromised, cancer patients, elderly |
| Disease resurgence | Pertussis resurgence related to waning immunity and refusal; measles resurgence in undervaccinated areas |
| Healthcare system burden | Hospitalizations, ICU care, long-term complications, costs |
| Economic impact | Outbreak control costs, contact tracing, lost productivity |
Catch-Up Schedule
General Principles
| Principle | Description |
|---|---|
| Minimum intervals | Maintain minimum intervals between doses (do not restart series) |
| Simultaneous vaccination | All vaccines can be given simultaneously (separate injection sites) |
| Delayed start | If a series was delayed, continue from current point (do not restart) |
| Shortest intervals | If doses were given too close together, those doses are invalid |
| Age-appropriate dosing | Use age-appropriate formulation (DTaP vs Tdap; PCV13 vs PPSV23) |
Accelerated Catch-Up
| Vaccine | Minimum Interval Between Doses | Notes |
|---|---|---|
| HepB | 4 weeks between D1 and D2; 8 weeks between D2 and D3 (with 16 weeks between D1 and D3) | Minimum age for final dose: 24 weeks |
| DTaP | 4 weeks between D1-D3; 6 months between D3-D4; 6 months between D4-D5 | D5 not needed if D4 given at age 4+ |
| IPV | 4 weeks between D1-D3; 6 months between D3-D4 | Minimum age for final dose: 4 years |
| MMR | 4 weeks between D1 and D2 | |
| Varicella | 4-8 weeks between D1 and D2 | |
| HepA | 6 months between D1 and D2 | |
| HPV | Minimum 4 weeks between D1-D2; 12 weeks between D2-D3; 5 months between D1-D3 | 2 doses if 9-14 at start (0, 6-12 months) |
| MenACWY | 8 weeks between doses |