Table 1.
Transmissibility of, modes of transmission of and transmission-based precautions for common respiratory viruses in humans
| Transmissibility and transmission | HCoV | IV | MeV | PIV | RSV | HMPV | VZV | RhV | HAdVa |
|---|---|---|---|---|---|---|---|---|---|
| Transmissibilityb | |||||||||
| Basic reproduction number (R0) | 0.5–8.0 | 1.0–21.0 | 1.4–770 | 2.3–2.7 | 0.9–21.9 | – | 1.2–16.9 | 1.2–2.7 | 2.3–5.1 |
| Household SAR (%) | 0–38.2 | 1.4–38.0 | 52.0–84.6 | 36.0–67.0 | 11.6–39.3 | – | 61.0–78.1 | 28.0–58.0 | – |
| Evidence for direct contact transmissionc | |||||||||
| Infectious virus survival on experimentally contaminated handsd | ✓ | ✓ | – | ✓ | ✓ | – | ✓ | ✓ | – |
| Virus genetic material recovered on naturally contaminated hands | – | – | – | – | – | – | ✓ | ✓ | – |
| Infectious virus recovered on naturally contaminated hands | – | – | – | – | – | – | – | ✓ | – |
| Transfer of virus genetic material between hands experimentally | – | ✓ | – | – | – | – | – | – | – |
| Transfer of infectious virus between hands experimentally | – | – | – | – | ✓ | – | – | ✓ | – |
| Infection initiated via exposure to infectious virus on hands demonstrated in volunteer studies | – | – | – | – | – | – | – | ✓ | – |
| Transmission of laboratory-confirmed infection via hands demonstrated in observational studies | ✓ | ✓ | ✓ | – | ✓ | – | – | – | ✓ |
| Transmission of laboratory-confirmed infection via hands demonstrated in volunteer studies | – | ✓ | – | – | – | – | – | ✓ | – |
| Evidence for indirect contact (fomite) transmissionc | |||||||||
| Infectious virus survival on experimentally contaminated surfacesd | ✓ | ✓ | – | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Virus genetic material recovered on naturally contaminated surfaces | ✓ | ✓ | ✓ | ✓ | – | – | ✓ | ✓ | ✓ |
| Infectious virus recovered on naturally contaminated surfaces | ✓ | ✓ | – | – | – | – | – | ✓ | ✓ |
| Transfer of virus genetic material between hands and surfaces experimentally | – | ✓ | – | – | – | – | – | ✓ | – |
| Transfer of infectious virus between hands and surfaces experimentally | – | ✓ | – | ✓ | ✓ | – | – | ✓ | ✓ |
| Infection initiated via exposure to infectious virus on surfaces demonstrated in volunteer studies | – | – | – | – | – | – | – | – | – |
| Transmission of laboratory-confirmed infection via surfaces demonstrated in observational studies | ✓ | – | – | – | – | – | ✓ | – | – |
| Transmission of laboratory-confirmed infection via surfaces demonstrated in volunteer studies | – | – | – | – | ✓ | – | – | ✓ | – |
| Evidence for droplet transmissionc,e | |||||||||
| Infectious virus survival in experimentally generated droplets | – | ✓ | – | (✓) | – | – | – | – | – |
| Virus genetic material recovered in droplets in human exhaled breathf | (✓) | (✓) | – | (✓) | (✓) | (✓) | – | (✓) | – |
| Infectious virus recovered in droplets in human exhaled breath | – | (✓) | – | – | – | – | – | – | – |
| Virus genetic material recovered in droplets in the air | (✓) | (✓) | (✓) | – | (✓) | – | – | (✓) | (✓) |
| Infectious virus recovered in droplets in the air | – | – | – | – | (✓) | – | – | – | – |
| Infection initiated via exposure to infectious virus in droplets demonstrated in volunteer studies | ✓ | ✓ | – | – | ✓ | ✓ | – | ✓ | (✓) |
| Transmission of laboratory-confirmed infection via droplets demonstrated in observational studies | – | – | – | – | – | – | – | – | – |
| Transmission of laboratory-confirmed infection via droplets demonstrated in volunteer studies | – | – | – | – | – | – | – | – | – |
| Evidence for aerosol transmissionc,e | |||||||||
| Infectious virus survival in experimentally generated aerosols | ✓ | ✓ | ✓ | ✓ | ✓ | – | – | – | ✓ |
| Virus genetic material recovered in aerosols in human exhaled breathf | ✓ | ✓ | – | ✓ | ✓ | ✓ | – | ✓ | – |
| Infectious virus recovered in aerosols in human exhaled breath | – | ✓ | – | – | – | – | – | – | – |
| Virus genetic material recovered in aerosols in the air | ✓ | ✓ | ✓ | ✓ | ✓ | – | ✓ | ✓ | ✓ |
| Infectious virus recovered in aerosols in the air | ✓ | ✓ | – | – | ✓ | – | – | – | – |
| Infection initiated via exposure to infectious virus in aerosols demonstrated in volunteer studies | – | ✓ | – | – | – | – | – | ✓ | ✓ |
| Transmission of laboratory-confirmed infection via aerosols demonstrated in observational studies | ✓ | ✓ | ✓ | – | – | – | ✓ | – | – |
| Transmission of laboratory-confirmed infection via aerosols demonstrated in volunteer studies | – | – | ✓ | – | – | – | ✓ | ✓ | – |
| Transmission-based precautions in health-care settingsg | |||||||||
| Contact precautionsh | Y | Y | N | Y | Y | Y | N | Y | Y |
| Droplet precautions | Y | Y | N | Y | Y | Y | N | Y | Y |
| Airborne precautions | N | N | Y | N | N | N | Y | N | N |
See Supplementary Table 1 for supporting references as well as evidence stratified by coronavirus types or influenza virus (IV) types/subtypes. Human bocavirus is not shown due to a lack of evidence regarding all modes of transmission. HAdV, human adenovirus; HCoV, human coronavirus; HMPV, human metapneumovirus; MeV, measles virus; N, not recommended; PIV, parainfluenza virus; RhV, rhinovirus; RSV, respiratory syncytial virus; SAR, secondary attack rate; VZV, varicella zoster virus; Y, recommended; ✓, evidence identified; (✓), evidence identified only in particles with aerodynamic diameter between 5 and 100 µm (applicable to droplet transmission only); –, evidence not found. aHAdV types that are considered mainly respiratory (but not enteric) are included. bThe range of reported estimates of the mean or median is provided. Estimates of household SAR in the absence of interventions were extracted where possible. cObservational studies include epidemiological or outbreak investigations, whereas volunteer studies include challenge studies or randomized (controlled) trials. dData include contamination by direct virus inoculation or contamination by volunteers who were experimentally infected. eParticles with aerodynamic diameter larger than 5 µm are traditionally defined as droplets, whereas those with a smaller aerodynamic diameter are defined as aerosols. However, there is ongoing discussion on redefining the particle size threshold between droplets and aerosols (see the section Terminology and defining features of modes of transmission). Therefore, for evidence on droplet transmission, evidence is provided in parentheses if evidence of virus recovery is identified only in particles with aerodynamic diameter between 5 and 100 µm. Air samples collected without size fractionation but that were collected more than 2 m from a known source (for example, an infected individual) are considered as evidence suggestive of aerosols. fEvidence for virus genetic material recovered in droplets or aerosols in human exhaled breath for PIV, RSV and HMPV is based on the author’s own additional data of the published study93. gEach precaution represents a set of infection prevention and control practices and personal protective equipment recommended by the WHO for health-care workers during routine patient care (excluding aerosol-generating procedures) within health-care facilities, with consideration of the current understanding on the modes of transmission of the respective pathogen. hFor IV, contact precautions are recommended for zoonotic IV only but not for endemic or pandemic IV.