Immunity, vaccine types, EPI schedule and non-EPI vaccines

Overview

Immunisation is the most cost-effective child health intervention. In Pakistan it is delivered through the Expanded Programme on Immunization (EPI), which protects infants against the main vaccine-preventable killers. House officers need to know the schedule, routes, contraindications, cold chain and adverse events, and how to counsel parents.

Types of immunity

Herd immunity

• When a large proportion of a community is immune, the chain of person-to-person spread breaks, so unvaccinated people are indirectly protected.
• Depends on infections in the community, vaccination coverage and herd structure (births, deaths and migration change it constantly).
• It does not need 100% coverage to stop spread.
• Tetanus is the exception: it does not spread person to person, so every individual must be vaccinated.
• OPV gives extra herd effect because vaccine virus is shed in stool and spreads to contacts.

Vaccine types

Live versus killed

• Live vaccines are generally more potent: the organism multiplies, presents all antigens, and (for OPV) induces gut immunity. Usually one dose gives protection (a second dose catches the few who did not respond); OPV needs several doses.
• Killed vaccines need several doses and boosters, but cannot cause disease.
• Two live vaccines: give on the same day at different sites, or at least 4 weeks apart (Park gives at least 3 weeks).
• Delay live vaccines after immunoglobulin or blood (measles-containing vaccines by several months).

Why conjugate vaccines

Children under 2 years respond poorly to polysaccharide antigens because the response is T-cell independent (no memory). Linking the sugar to a carrier protein makes it T-cell dependent, so infants make good antibody and memory.

EPI schedule (Pakistan)

The current national schedule is set by the Federal Directorate of Immunization in the National Immunization Policy 2022 (Annexure I). It adds a hepatitis B birth dose, the typhoid conjugate vaccine (TCV), measles-rubella (MR) in place of measles-only vaccine and a second IPV dose to the older schedule printed in Akbar's textbook.

• Fully immunised child: has received all the doses above, including two IPV doses.
• Catch-up after the first birthday: two MR doses at least 6 months apart, two IPV doses 6 months apart, and one TCV dose.
• Some provinces add a DPT booster at 4-5 years (Punjab).
• Schedules change as vaccines are added. Official source: National Immunization Policy 2022, Federal Directorate of Immunization (checked 6 November 2026).

• Minimum interval between doses of the primary DPT/OPV series: 4 weeks. If doses are late, do not restart; just continue the course.
• Pregnant women receive tetanus toxoid (Td) to prevent neonatal tetanus.
• Vitamin A is given with immunisation contacts every 6 months from 6 months of age (IMNCI).

EPI target diseases

Tuberculosis (severe childhood forms), poliomyelitis, diphtheria, pertussis, tetanus (including neonatal), measles, hepatitis B, Haemophilus influenzae type b disease, pneumococcal disease, rotavirus diarrhoea, plus diseases added later (typhoid, rubella).

Key facts about individual EPI vaccines

BCG

• Live attenuated Mycobacterium bovis. Most widely used vaccine in the world.
• Protects best against severe childhood TB (TB meningitis and miliary TB), about 80%; much less against adult pulmonary TB (about 50%).
• Normal reaction: wheal disappears in 30 minutes; papule at 2-3 weeks, which may form a small pustule or ulcer, heals within weeks and leaves a scar.
• Complications: abscess, ulceration, axillary lymphadenitis, keloid; disseminated BCG in immunodeficiency.
• Koch phenomenon: an accelerated reaction (within days, completes in about 10 days) in a child already sensitised to TB.
• Not given in symptomatic HIV or other immunodeficiency.

Polio vaccines

• OPV is not contraindicated by breastfeeding, mild diarrhoea or antibiotics.
• A child who has had polio still needs vaccine (three poliovirus types).
• Low seroconversion in hot countries: loss of cold chain and interference from other gut enteroviruses.

DPT (in pentavalent)

• Common: fever and local pain within 12-24 hours; give paracetamol. Not a reason to stop.
• Do not give pertussis component again after: anaphylaxis, or encephalopathy within 7 days of a dose.
• Akbar: if convulsions within 72 hours of DPT, give DT for remaining doses. Defer in a progressive or unstable neurological disorder (infantile spasms, uncontrolled epilepsy) until stable.
• Precautions: very high fever, persistent inconsolable crying for 3 hours or more, hypotonic-hyporesponsive (shock-like) episode within 48 hours.

Measles

• Live; subcutaneous; reconstituted vaccine is discarded after 4 hours.
• Mild fever, rash or conjunctivitis may follow in 5-15% (Park), usually a week later.
• Give to malnourished children on admission (and again on discharge), because malnutrition increases measles mortality.

Hepatitis B

• Recombinant; 3 doses (birth or 6 weeks, then in pentavalent). Deltoid in older children; anterolateral thigh in infants.
• Baby of an HBsAg-positive mother: HBIG 0.5 mL in the first 12 hours of life plus hepatitis B vaccine at a different site, then complete the course; check anti-HBs and HBsAg after the series.
• Successful vaccination gives anti-HBs alone in serum (no anti-HBc).

Rotavirus and PCV

• Rotavirus vaccine is oral only; first dose from 6 weeks, doses at least 4 weeks apart, and completed early in infancy because intussusception risk rises with age.
• PCV protects against pneumonia, meningitis and bacteraemia.

Contraindications and precautions

Vaccine storage, handling and administration

Cold chain

The cold chain keeps vaccines at the right temperature from manufacturer to child. Most vaccines need +2°C to +8°C.

• Equipment: walk-in cold rooms (regional), deep freezers (−15 to −25°C), ice-lined refrigerators (ILR, +2 to +8°C), cold boxes, vaccine carriers, day carriers, ice packs (water only, no salt).
• In the ILR keep vaccines in the basket; do not let freeze-sensitive vaccines touch frozen ice packs; record the temperature twice a day.
• Frozen "T" vaccines or hepatitis B, or vials with floccules: discard (freezing destroys the adsorbed antigen; a shake test can detect freeze damage).
• Reconstituted BCG and measles: use within 4 hours, then discard. Cool diluents before mixing to avoid thermal shock.
• Protect from sunlight and antiseptics; follow early expiry, first out.
• Risk of cold chain failure is highest at the village and session level.

Vaccine vial monitor (VVM)

A heat-sensitive square inside a circle on the label that darkens irreversibly with cumulative heat exposure.

Administration

• Safe injection: auto-disable syringes, one needle one child, safety box disposal.
• Sites: IM in the anterolateral thigh in infants (deltoid in older children); BCG intradermal in the upper arm; measles subcutaneous.
• Several vaccines can be given at the same visit at different sites.
• Observe for 15-30 minutes after vaccination; have adrenaline ready.

Adverse events following immunisation (AEFI)

An AEFI is any unwanted medical event after immunisation, whether or not caused by the vaccine.

Cause-specific categories (WHO):

1. Vaccine product-related reaction
2. Vaccine quality defect-related reaction
3. Immunisation error-related (wrong storage, dose, route, contamination): the most preventable
4. Immunisation anxiety-related (fainting, hyperventilation)
5. Coincidental event

Minor (common) reactions:

• Local pain, swelling and redness (about 10%; up to half with whole-cell DTP).
• Fever, irritability, malaise (more with DTP).
• Measles vaccine: mild fever and rash; BCG: expected papule and scar.

Serious reactions (rare): anaphylaxis, encephalopathy, hypotonic-hyporesponsive episode, vaccine-associated paralytic polio, disseminated BCG. Serious AEFIs and clusters must be reported and investigated.

Caregiver counselling

• Explain which diseases are prevented and when to come back; give and fill the vaccination card.
• Warn about expected minor reactions: fever and local soreness for a day or two; give paracetamol; do not apply anything to the BCG site.
• Seek help urgently for high fever, fits, persistent crying, breathing difficulty, or a large swelling.
• Reassure that mild illness, malnutrition, prematurity or breastfeeding are not reasons to miss a dose.
• Breastfeeding can continue normally around OPV.

Non-EPI vaccines

Quick revision

• Passive = immediate, short, no memory; active = slow, lasting, memory.
• Herd immunity protects the unvaccinated; not for tetanus.
• Live: BCG, OPV, measles/MR/MMR, rotavirus, varicella, yellow fever, Ty21a.
• Toxoids: diphtheria, tetanus. Conjugates: Hib, PCV, meningococcal, TCV.
• EPI (Akbar): birth BCG + OPV-0; 6-10-14 weeks pentavalent, OPV, PCV (rotavirus 6 and 10, IPV 14); measles 9 and 15 months. Check the current schedule.
• OPV is the most heat-sensitive; never freeze DPT, TT, hepatitis B or diluents.
• VVM: inner square equal to or darker than circle → discard.
• Reconstituted BCG and measles: discard after 4 hours.
• Vaccinate despite minor illness, malnutrition, prematurity.

Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Park's Preventive and Social Medicine).

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