Transmission route and clinical characteristics of highly contagious diseases
| Disease | TB | Influenza | Measles, mumps and varicella | Adenovirus | COVID-19 |
| Transmission routes | Airborne, ?prolonged contact | Droplet, fomite ? airborne | Airborne (measles, varicella), droplets (mumps) | Droplet, fomite | Droplet, ?fomite ?airborne |
| Presymptom transmission | Unclear but less likely | Yes, 12 hours before symptom onset, but less contagious | Yes (during prodrome but before rash for measles, yes (varicella 1–2 days before rash), yes mumps (2 days before parotitis) | Unknown but unlikely | Yes |
| Incubation period | Weeks months | 1–4 days | 12–25 days mumps, 10–12 days measles, 10–20 days varicella | 2–14 days | 1–14 days (median 4–6 days) |
| Isolation period | Until appropriate treatment started | Not known | Varicella: until rash ‘crusted’; measles: until 4 days after rash onset; mumps: ‘from several days before the parotid swelling to several days after it appears’ (PHE) | Not known | 7 days for mild/moderate disease and 14 days for severe disease |
?=Uncertain as robust conclusions cannot be formulated from current data.
PHE, Public Health England; TB, tuberculosis.