2.2 Immunization Schedules (NACI) & Vaccine-Preventable Diseases across Lifespan

Immunization Schedules (NACI) & Vaccine-Preventable Diseases

The National Advisory Committee on Immunization (NACI) provides expert advice to the Public Health Agency of Canada (PHAC) regarding the safety, efficacy, and clinical use of vaccines. While healthcare administration is governed provincially and territorially, NACI recommendations form the gold standard for Canadian immunization practice.

On the MCCQE Part I, vaccine questions test exact timing, catch-up schedules, maternal-fetal immunization, special populations (e.g., post-splenectomy), and absolute versus false contraindications.

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Routine Pediatric Immunization Schedule

Canadian pediatric immunization schedules follow a structured sequence designed to establish immunity before exposure to high-mortality childhood pathogens.

Pediatric Vaccine Milestones

• 2 Months: DTaP-IPV-Hib-HB (Hexavalent vaccine: Diphtheria, Tetanus, acellular Pertussis, Inactivated Polio, Haemophilus influenzae type b, Hepatitis B), Pneumococcal Conjugate (Pneu-C-13 / Pneu-C-15 / Pneu-C-20), Rotavirus (oral).
• 4 Months: Second doses of DTaP-IPV-Hib-HB, Pneu-C, and Rotavirus.
• 6 Months: Third dose of DTaP-IPV-Hib-HB (and third dose of Rotavirus/Pneu-C depending on specific formulation used).
• 12 Months: Measles-Mumps-Rubella (MMR), Meningococcal C Conjugate (Men-C-C) or Men-C-ACYW-135, Pneumococcal Conjugate booster (Pneu-C).
• 18 Months: DTaP-IPV-Hib booster, Measles-Mumps-Rubella-Varicella (MMRV).
• 4–6 Years (Pre-school Booster): DTaP-IPV or Tdap-IPV, MMRV.
• Grade 6 / Adolescence (11–12 Years): Human Papillomavirus (HPV: 9vHPV, 2-dose series given 0 and 6 months if started before age 15), Hepatitis B (if not completed in infancy), Quadrivalent Meningococcal Conjugate (Men-C-ACYW-135 booster).
• 14–16 Years: Tdap booster (Tetanus, reduced Diphtheria, acellular Pertussis).

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Adult & Elderly Immunization Protocols

Adult immunization focuses on waning immunity, age-related immunosenescence, and chronic disease risk reduction.

Primary Adult Vaccines

1. Tetanus, Diphtheria, Pertussis (Tdap / Td):
   • Adults should receive one dose of Tdap in adulthood if not previously received, followed by a Td booster every 10 years.
   • Maternal Immunization: NACI recommends Tdap vaccination during EVERY pregnancy, ideally between 27 and 32 weeks gestation (regardless of prior Tdap interval). This maximizes transplacental transfer of maternal anti-pertussis antibodies, protecting the newborn during the vulnerable first two months of life.
2. Pneumococcal Vaccines:
   • Pneu-C-20 (Conjugate): Recommended for all adults aged 65 and older, and for adults aged 18–64 with high-risk conditions (asplenia, immunocompromise, chronic kidney/heart/lung disease, CSF leak, cochlear implants).
   • Alternative: Pneu-C-15 followed by Pneu-P-23 (Pneumococcal Polysaccharide 23-valent) at least 1 year later.
3. Herpes Zoster (Shingles):
   • Recombinant Zoster Vaccine (RZV / Shingrix): 2-dose series (administered 2 to 6 months apart) for all adults aged 50 and older, regardless of prior history of varicella infection or receipt of live zoster vaccine (Zostavax). RZV is also recommended for immunocompromised adults aged 18 and older.
4. Annual Influenza Vaccine:
   • Recommended for all individuals aged 6 months and older.
   • High-dose or adjuvanted inactivated influenza vaccine is preferred for adults aged 65 and older due to superior immunogenicity.

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Immunization in Special & High-Risk Populations

Asplenia & Functional Asplenia

Anatomical splenectomy (e.g., trauma, staging) or functional asplenia (e.g., Sickle Cell Disease) creates severe susceptibility to overwhelming post-splenectomy infection (OPSI) caused by encapsulated organisms.

• Required Vaccines:
  • Pneumococcal: Pneu-C-20 (or Pneu-C-15 + Pneu-P-23).
  • Meningococcal: Quadrivalent Men-C-ACYW-135 AND Meningococcal B (4CMenB).
  • Haemophilus influenzae type b (Hib): 1 dose if not previously vaccinated.
  • Annual Influenza Vaccine.
• Timing: Administer vaccines at least 2 weeks prior to elective splenectomy, or 2 weeks after emergency splenectomy.

Immunocompromised Individuals & Pregnancy

• Live Attenuated Vaccines: Includes MMR, Varicella, Yellow Fever, Oral Typhoid, Rotavirus, and Live Attenuated Influenza Vaccine (LAIV).
• Absolute Contraindications: Live vaccines are strictly contraindicated in:
  1. Pregnancy (theoretical risk of fetal infection; women should avoid pregnancy for 4 weeks post-vaccination).
  2. Severe Immunocompromise (e.g., CD4 count < 200/mcL in HIV, active chemotherapy, high-dose systemic steroids ≥20 mg/day prednisone equivalent for >2 weeks, biologic TNF-alpha inhibitors).
• Inactivated Vaccines: Safe in pregnancy and immunocompromised patients (e.g., inactivated flu, Tdap, Hepatitis B, COVID-19 mRNA).

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True vs. False Vaccine Contraindications

Exam Trap: Egg allergy is NO LONGER a contraindication for any influenza vaccine in Canada according to NACI guidelines. Do NOT delay, withhold, or refer patients with egg allergies to allergy specialists prior to administering routine flu vaccines.

Clinical Scenario: A 28-week pregnant 31-year-old G2P1 presents for prenatal assessment. Her medical record shows she received a Tdap booster 2 years ago following a clean laceration. What is the correct management regarding her immunization?
Answer: Administer the Tdap vaccine today. NACI guidelines mandate Tdap administration during every single pregnancy, regardless of the interval since her last tetanus or pertussis-containing vaccine. This provides peak transplacental IgG antibody transfer to protect her neonate against severe pertussis infection in early infancy.