What is the recommended vaccination schedule for a 3-year-old boy who has never been vaccinated?

Catch-Up Vaccination for an Unvaccinated 3-Year-Old

This child should begin an accelerated catch-up vaccination schedule immediately, with multiple vaccines administered simultaneously at the first visit following minimum age and interval requirements, as this approach is safe, effective, and critical to rapidly establish protection against life-threatening vaccine-preventable diseases. 1, 2

Immediate Action at Today's Visit

Administer all age-appropriate vaccines simultaneously at separate anatomic sites to maximize protection and minimize the number of visits required for catch-up. 1, 2 The immune response to one vaccine is not negatively affected by simultaneous administration of others. 2

Vaccines to Give Today (First Visit):

• DTaP (Diphtheria, Tetanus, Pertussis) - First dose of the series 1
• IPV (Inactivated Poliovirus) - First dose 1
• MMR (Measles, Mumps, Rubella) - First dose (can be given as early as 12 months, this child is overdue) 1, 3
• Varicella - First dose 1, 3
• Hepatitis B - First dose 1, 3
• Hepatitis A - First dose (recommended for all children) 3
• PCV (Pneumococcal Conjugate) - Single dose is sufficient for healthy children ≥24 months 3
• Hib (Haemophilus influenzae type b) - Single dose is sufficient for healthy children ≥15 months 3
• Influenza vaccine - If during flu season; requires two doses separated by at least 4 weeks for first-time recipients 1, 3

Follow-Up Schedule Using Minimum Intervals

The catch-up schedule divides into specific age groups (4 months-6 years and 7-18 years), with minimum intervals that must be respected to ensure adequate immune response. 4, 1, 2

Second Visit (4 Weeks After First Visit):

• DTaP - Second dose (minimum 4-week interval) 1
• IPV - Second dose (minimum 4-week interval) 1
• Hepatitis B - Second dose (minimum 4-week interval from first dose) 1

Third Visit (4 Weeks After Second Visit):

• DTaP - Third dose (minimum 4-week interval) 1
• IPV - Third dose (minimum 4-week interval) 1
• MMR - Second dose (minimum 4-week interval from first dose) 1, 3
• Varicella - Second dose (minimum 3-month interval preferred, but can be given at 4 weeks for catch-up) 3

Fourth Visit (6 Months After Second Hepatitis B Dose):

• Hepatitis B - Third dose (must be at least 8 weeks after second dose AND at least 16 weeks after first dose, AND not before 24 weeks of age) 4, 1
• Hepatitis A - Second dose (minimum 6-month interval from first dose) 1, 3

Fifth Visit (At Age 4-6 Years):

• DTaP - Fourth dose (must be given at least 6 months after third dose AND after age 4 years for final dose) 4, 1
• IPV - Fourth dose (final dose) 1, 3

Critical Principles for Catch-Up Vaccination

• Never restart a vaccine series regardless of time elapsed between doses - simply continue from where the child left off. 2
• Minimum intervals must be respected, but longer-than-recommended intervals do not reduce final antibody concentrations or require additional doses. 2
• Use combination vaccines when available to reduce the number of injections and improve compliance. 2
• Multiple vaccines can and should be administered simultaneously at separate anatomic sites when indicated, as this increases the likelihood of complete vaccination. 1, 2

Important Considerations and Pitfalls

• Screen for contraindications before each visit: severe allergic reactions to vaccine components, immunodeficiency, or moderate-to-severe acute illness. 2
• Rotavirus vaccine is NOT indicated for this 3-year-old, as it must be initiated between 6-14 weeks of age and completed by 8 months due to intussusception risk. 1
• Document all vaccines carefully to avoid unnecessary repeat doses and ensure proper tracking of the catch-up schedule. 1
• Counsel the father about the importance of maintaining the schedule going forward, as this child is at significantly increased risk for vaccine-preventable diseases until fully caught up. 1
• Annual influenza vaccination should continue every year, with two doses separated by 4 weeks if this is the first influenza season the child receives the vaccine. 1, 3

Addressing Common Barriers

The father's justification of travel and not being in town highlights a common barrier to vaccination completion. Emphasize that:

• Vaccine-preventable diseases pose serious morbidity and mortality risks, particularly for unvaccinated children. 5
• The accelerated catch-up schedule is designed specifically for situations like this, allowing rapid protection with proven safety and efficacy. 4, 1
• Missing vaccinations increases community transmission risk and leaves the child vulnerable during the critical early childhood period. 6