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Pancyprian Health Education study materials
Pancyprian Health Education study resources

Pancyprian Health Education: Communicable disease prevention, surveillance and immunisation

Pancyprian Health Education · Work through your exam, one topic at a time.

All guide sections

Communicable disease prevention, surveillance and immunisation

Scope

The exam tests the chain of infection, surveillance systems, outbreak investigation and vaccine immunology, including schedule and contraindication decisions.

Core rules

  • The chain of infection has six links: pathogen, reservoir, portal of exit, mode of transmission, portal of entry and susceptible host. Control can break any link.
  • Incubation is the time from exposure to symptoms; latent period is from exposure to infectiousness; infectious period is when transmission is possible. Isolation separates sick people; quarantine restricts exposed contacts.
  • R0 is the average secondary cases in a fully susceptible population. The herd immunity threshold is 1 − 1/R0. Effective R depends on immunity and behaviour.
  • Surveillance is passive (routine reporting), active (health workers seek cases), sentinel (selected sites) or syndromic (based on symptoms). Notification triggers outbreak investigation: verify, define cases, find cases, analyse, control, communicate.
  • Vaccine types include live attenuated (MMR, varicella), inactivated, subunit, toxoid, viral vector and mRNA. Live vaccines are avoided in pregnancy and severe immunosuppression. Vaccine efficacy is measured in trials; effectiveness is measured in real populations.
  • Standard precautions apply to all patients; transmission-based precautions are added for airborne, droplet and contact spread. Cold chain failure reduces potency, especially for live vaccines.

Worked example

Measles has an R0 of about 15. The herd immunity threshold is 1 − 1/15 ≈ 93%. If coverage is 90%, the effective reproduction number is roughly 15 × 0.10 = 1.5, so outbreaks can continue. The reasoning: the threshold is a proportion, and a few percentage points below it matter disproportionately in high-R0 diseases. Control therefore combines routine MMR coverage above 95%, catch-up campaigns and rapid contact tracing.

Traps

Do not confuse R0 with case fatality; do not use efficacy and effectiveness interchangeably; do not claim herd immunity protects everyone (immunocompromised people remain dependent on others); do not recommend live vaccines in pregnancy.