Let's talk infectious diseases, the reason for vaccines: ʸᵉˡˡᵒʷ ᶠᵉᵛᵉʳ

Yellow fever virus is an RNA virus that belongs to the genus Flavivirus. Yellow fever virus is transmitted to people primarily through the bite of infected Aedes or Haemagogus species mosquitoes. Mosquitoes acquire the virus by feeding on infected primates (human or non-human) and then can transmit the virus to other primates (human or non-human).

It is found in tropical and subtropical areas of Africa and South America. Yellow fever is a very rare cause of illness in U.S. travelers. It is diagnosed based on laboratory testing, a person’s symptoms, and travel history. There is no medicine to treat or cure infection.

The majority of people infected with yellow fever virus will either not have symptoms, or have mild symptoms and completely recover.

For people who develop symptoms, the time from infection until illness is typically 3 to 6 days. Initial symptoms include:

▪️Sudden onset of fever

▪️Chills

▪️Severe headache

▪️Back pain

▪️General body aches

▪️Nausea

▪️Vomiting

▪️Fatigue

▪️Weakness

▪️Most people with the initial symptoms improve within one week.

For some people who recover, weakness and fatigue (feeling tired) might last several months.

Severe symptoms include:

▪️High fever

▪️Jaundice

▪️Bleeding

▪️Shock

▪️Organ failure

Severe yellow fever disease can be deadly. Among those who develop severe disease, 30-60% die.

The most effective way to prevent infection from Yellow Fever virus is to prevent mosquito bites. Mosquitoes bite during the day and night. Use insect repellent, wear long-sleeved shirts and pants, treat clothing and gear, and get vaccinated before traveling, if vaccination is recommended for you.

Prior to 1741 doctors referred to the disease, and others that were similar to it, by a variety of names, such as pestilential fever, malignant fever, putrid bilious fever, and the like. Then the term yellow fever began to be used. The name comes from the yellowed appearance of the skin and eyes that results from damage to the liver: toxic materials build up in the blood and cause the tell-tale color to appear.

During the 1793 Yellow fever epidemic in Philadelphia Dr. Benjamin Rush observed the symptoms and spread of the disease closely, hoping to uncover some definite cause and means of prevention. Rush, however, did not seem to draw any conclusions about the presence of the mosquitoes in relation to yellow fever. He favored the “miasma” theory of the disease—literally “pollution”—which was widely accepted in Philadelphia at the time.

Yellow fever killed more than 13,000 people in the lower Mississippi Valley in 1878. At the time, it was one of the worst medical disasters in U.S. history. Marine Hospital Service Surgeon General John Woodworth reported to Congress that “Yellow fever should be dealt with as an enemy which imperils life and cripples commerce and industry.”

Spurred by the massive yellow fever-related casualties in the Spanish-American War, members of the U.S. Army Yellow Fever Commission, headed by Walter Reed, traveled to Cuba to study the disease in 1900. The Commission was successful with Jesse Lazear even giving his life toward the pursuit of an answer. It was determined that it was, in fact, caused through the transmission of mosquito bites.

Following this finding, efforts began to reduce and remove the mosquito population in areas where the disease was most evident. Workers drained or covered open water containers and fumigated areas to kill adult mosquitoes. Yellow fever cases began to drop, and reports of malaria dropped as well.

Due to the discovery that infected mosquitos were the culprits and there were preventative measures that could be taken, the last yellow fever epidemic on the North American continent occurred in 1905. But the need for a vaccine existed in other continents.

It wasn't until 1931 that a Yellow fever vaccine started to gain some traction. Max Theiler demonstrated that mice injected with serum from previously infected monkeys or humans were protected from yellow fever infection.

And finally, in 1936 Theiler and his colleagues successfully developed a live attenuated vaccine for yellow fever using tissue cultures prepared from embryonated chicken eggs. Among the many subcultures of the yellow fever virus in the laboratory, the one designated “17D” was used, giving the vaccine its name. He published results of U.S. vaccine trials in humans in 1937. The vaccine was easily adapted for mass production and became the universal standard.

Although the 17D yellow fever vaccine is highly effective, vaccination rates in at-risk regions remain lower than is necessary to prevent outbreaks. The World Health Organization warns that epidemics in unvaccinated populations can result in case-fatality ratios of more than 50%. WHO encourages both mass immunization efforts and routine infant immunization, as well as vaccination for travelers to countries where the disease is endemic. American travelers are required by WHO International Health Regulations to receive a yellow fever vaccination before visiting some countries in tropical South America and sub-Saharan Africa.

{You can find all the sources I used by clicking here.}