Communicable Disease Epidemiology, Surveillance and Immunisation

Transmission dynamics

• Chain: agent → reservoir → portal of exit → mode → portal of entry → susceptible host.
• Carriers: incubatory, convalescent, healthy; temporary or chronic. Dead‑end hosts: humans in JE, rabies, hydatid.
• Incubation (infection → symptoms) sets quarantine length; serial interval (onset → onset); generation time (infection → infection).
• HIT = 1 − 1/R₀; critical coverage Vc = HIT / VE. Measles R₀ 12–18 → about 93–95%.
• Isolation = infected; quarantine = exposed well persons (longest incubation period).
• Vector transmission: propagative (dengue, plague), cyclo‑developmental (filaria), cyclo‑propagative (malaria).

Disinfection

• Spaulding: critical → sterilise; semi‑critical → HLD; non‑critical → clean or low‑level disinfect.
• Autoclave 121 °C, 15 psi, 15–20 min (G. stearothermophilus); hot‑air oven 160 °C × 2 h (B. atrophaeus).
• 0.5% chlorine for spills and decontamination; clean before disinfecting. Concurrent vs terminal disinfection.

Surveillance and outbreaks

• IDSP (2004, NCDC) → IHIP (2021): S (health worker), P (MO), L (lab). Weekly Monday–Sunday; immediate outbreak alerts; RRTs.
• Types: passive, active, sentinel, syndromic, event‑based, lab, environmental.
• IHR 2005: notify WHO within 24 h of assessing a potential PHEIC.
• Outbreak steps: prepare → confirm outbreak → verify diagnosis → case definition → find cases (line list) → describe → hypothesise → test (attack rates/RR or OR) → control → communicate. Exposure never goes in the case definition.

Vaccines and UIP

• Live: BCG, OPV, MR, RVV, live JE (avoid in pregnancy and immunosuppression). Toxoids: T, D. Conjugate: Hib, PCV, TCV.
• Live parenteral vaccines: same day or ≥ 4 weeks apart. Never restart a series.
• Schedule (MoHFW AR 2025–26): birth (BCG, OPV‑0, HepB‑0) → 6/10/14 weeks (OPV, Penta, RVV; fIPV at 6 and 14; PCV at 6 and 14) → 9–12 months (MR‑1, PCV‑B, fIPV‑3, JE‑1, Vit A) → 16–24 months (MR‑2, DPT‑B1, OPV‑B, JE‑2) → 5–6 years DPT‑B2 → 10 and 16 years Td; pregnancy Td‑1, Td‑2 or booster.
• 🆕 28 February 2026: single‑dose HPV for 14‑year‑old girls. FIC (NFHS‑6) 87.1%.
• Zero‑dose = no DTP‑1/Penta‑1. Dropout = (Penta‑1 − Penta‑3)/Penta‑1 × 100 (aim < 10%).

Cold chain and AEFI

• ILR +2 to +8 °C; deep freezer −15 to −25 °C. OPV most heat‑sensitive; Hep B, Penta, DPT, Td, PCV, IPV freeze‑sensitive.
• VVM = cumulative heat only; stage 3–4 discard. Shake test for freezing. FEFO.
• Open vial policy: eligible liquid vaccines up to 28 days; reconstituted BCG/MR/JE discard within 4 h or at session end.
• Wastage factor = 1/(1 − wastage rate).
• AEFI causes: product, quality defect, immunisation error, anxiety, coincidental. TSS cluster = contaminated reconstituted vial. Adrenaline 1:1,000 0.01 mL/kg IM; observe 30 min.

Polio and MR

• Last WPV case India 13 January 2011; certified 27 March 2014. WPV2 (2015), WPV3 (2019) eradicated; WPV1 in Pakistan and Afghanistan.
• AFP < 15 years: 2 stools ≥ 24 h apart within 14 days; 60‑day follow‑up; NPAFP ≥ 2/100,000; stool adequacy ≥ 80%.
• Measles: R₀ 12–18; 3 C's; Koplik spots; communicable 4 days before to 4 days after rash; vitamin A × 2 days. CRS: cataract, deafness, PDA; highest risk < 12 weeks. MR elimination target 2026.