List of Most Contagious Diseases

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Infographic comparing the maximum basic reproduction numbers (R0) of various contagious diseases, using diagrams of a red contagious person spreading infection to multiple blue figures, with R0 values increasing from 2 for Ebola and influenza up to 18 for measles.

DTaP vaccine vial labeled for diphtheria, tetanus, and pertussis sits in front of a syringe, green medical gloves, and a disposable face mask.

Close-up of skin with numerous red, raised spots and blisters characteristic of a chickenpox rash.

Disinfection workers wearing masks and gloves spray and wipe down railings at Incheon International Airport in South Korea during the COVID-19 pandemic.

Rusty warning sign in French reading Attention Ebola, with instructions not to touch or handle animals found dead in the forest, displayed beside a road in Makoua, Congo.

Boxes of Ixiaro, Twinrix, and Rabipur vaccines are arranged on a table, showing their labels for Japanese encephalitis, hepatitis A and B, and rabies protection.

Influenza virus

List of Most Contagious Diseases: Media

Images

Infographic comparing the maximum basic reproduction numbers (R0) of various contagious diseases, using diagrams of a red contagious person spreading infection to multiple blue figures, with R0 values increasing from 2 for Ebola and influenza up to 18 for measles.

Basic reproduction number of select viral diseases

The contagiousness of infectious pathogens is measured by R₀ (R naught),...

Encyclopædia Britannica, Inc.

DTaP vaccine vial labeled for diphtheria, tetanus, and pertussis sits in front of a syringe, green medical gloves, and a disposable face mask.

DTaP vaccine

Pertussis, also known as whooping cough, can be prevented through vaccination with...

© Sherry Young/Dreamstime.com

Close-up of skin with numerous red, raised spots and blisters characteristic of a chickenpox rash.

Chickenpox

A close-up view of skin covered with the red raised papules that are characteristic...

©Gabriel Blaj/Dreamstime.com

Disinfection workers wearing masks and gloves spray and wipe down railings at Incheon International Airport in South Korea during the COVID-19 pandemic.

COVID-19, South Korea

Maintenance workers disinfecting a handrail at Incheon International Airport outside...

Chung Sung-Jun/Getty Images News

Mumps

Mumps

A child with bilateral swelling in the neck due to mumps.

Dr. Heinz F. Eichenwald—Centers for Disease Control and Prevention (CDC) (Image Number: 3186)

Tuberculosis

Tuberculosis

A doctor examining chest X-rays of patients infected with tuberculosis, which remains...

© imageBROKER—REX/Shutterstock.com

Rusty warning sign in French reading Attention Ebola, with instructions not to touch or handle animals found dead in the forest, displayed beside a road in Makoua, Congo.

Ebola virus disease outbreak

A sign warning visitors of an Ebola outbreak, September 27, 2013, Makoua, Republic...

© Sergey Uryadnikov/Shutterstock.com

Boxes of Ixiaro, Twinrix, and Rabipur vaccines are arranged on a table, showing their labels for Japanese encephalitis, hepatitis A and B, and rabies protection.

Vaccines

The vaccines Ixiaro for protection against Japanese encephalitis, Twinrix for protection...

© Ole Spata—picture alliance/Getty Images

Influenza virus

Influenza virus

A colored transmission electron micrograph showing influenza viruses (red) at the...

Science Photo Library/SuperStock

Interactives

Measles

Measles

Interactive line chart showing reported measles cases in the United States from 1960–2024.

Encyclopædia Britannica, Inc.