At what stage is smallpox most contagious?

This is an automatically translated article.

The article is professionally consulted by Master, Doctor Vu Quoc Anh - Pediatrician - Department of Pediatrics - Neonatology - Vinmec Danang International General Hospital. Dr. Anh has nearly 10 years of experience as a resident doctor and treating doctor at Hue Central Hospital and Danang Children's Hospital. Her strength is diagnosis and treatment of pediatric diseases; Pediatric resuscitation and first aid.
Smallpox is fatal in 30% of cases. Early symptoms include high fever and fatigue. The virus then causes a characteristic rash, especially on the face, arms, and legs. The spots become filled with clear liquid, turn pus, and then form a crust, which eventually dries and falls off.

1. Smallpox symptoms through stages

1.1 The incubation period This phase can last from 7 to 19 days (although the average time is 10 to 14 days).
At this stage, the disease is not contagious. The incubation period is the amount of time the virus stays in a person's body before they look or feel sick. This stage is usually asymptomatic.
1.2 The onset phase This phase lasts from 2 to 4 days.
Smallpox is contagious during this stage, but is most contagious during the next 2 stages (early rash and pus-scaly rash).
The first symptoms include:
High fever Headache and body Nausea. vomiting At this point, the body begins to show signs of illness.
1.3 Early Rash Stage This phase lasts about 4 days. This is the period when smallpox is most contagious. The rash begins as small red spots on the tongue and in the mouth. These spots change into sores that break open and spread large amounts of the virus into the mouth and throat. The patient continues to have a fever.
When the sores in the mouth start to break open, a rash will appear on the skin, starting on the face and spreading to the arms and legs, then the hands and feet. Usually, it spreads to all parts of the body within 24 hours. At this point, the fever begins to subside and the person may begin to feel better.
By day four, the sores on the skin are filled with a cloudy fluid and often have a depression in the center.

1.4 The rash - pus - scabs stage This stage lasts about 10 days.
At this stage, the sick person is still contagious. The sores become pustules (raised strongly, often round and firm to the touch). After about 5 days, the pustules begin to crust and then crust over. By the end of the second week after the rash appeared, most of the sores had scabbed over.
1.5 Scaling phase This phase lasts about 6 days. The scales begin to fall off, leaving marks on the skin. Three weeks after the rash appears, most of the scabs will fall off.
1.6 The scab phase is no longer contagious.
Four weeks after the rash appeared, all scabs should have fallen off. Once all the scabs have fallen off, the person is no longer able to transmit the disease to others.

2. When is smallpox most contagious?

The early rash stage is the most contagious. This phase lasts about 4 days with manifestations: red spots on the tongue and in the mouth, a generalized rash accompanied by fever.
The rate of transmission of smallpox is generally slower than that of diseases such as measles or chickenpox. Patients transmit smallpox mainly to family members and friends because by the time the patient is contagious, they are often sick and in bed; Large outbreaks in schools are uncommon.

3. How to prevent smallpox?

The smallpox vaccine protects people from smallpox by helping their bodies develop immunity to smallpox. The vaccine is made from a virus called vaccinia, which is a poxvirus similar to the virus that causes smallpox, but less harmful. The smallpox vaccine contains a live vaccine virus, not a killed or attenuated virus like many other vaccines.
For most people with healthy immune systems, a live virus vaccine is effective and safe. Sometimes a person receiving a live virus vaccine experiences mild symptoms such as a rash, fever, and headache. In some groups of people, complications from the vaccinia virus can be serious.
Other live virus vaccines currently in use include measles, mumps, rubella, and chickenpox.
Smallpox vaccination can protect you from smallpox for about 3 to 5 years. After that time, the protection decreases. If you need long-term protection, you may need a booster vaccine.
Historically, the vaccine has been effective in preventing smallpox infection in 95% of those vaccinated. In addition, the vaccine has been shown to prevent or significantly reduce infection when given within a few days of a person's exposure to the variola virus.
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