Dengue virus is transmitted by the bite of certain mosquitoes. Although these mosquitoes are not selective in who they bite, the dengue vaccine is only recommended for a specific group of young people.

The disease

What is dengue?

Dengue is an infection caused by four closely related viruses, referred to as dengue virus types 1-4. These viruses are carried by certain mosquitos, and the bite of the mosquito leads to the infection in people. The four viruses are part of the flaviviridae family and are closely related to other viruses that are carried by ticks or mosquitos and cause human disease, such as yellow fever, West Nile virus and Zika virus.

People infected with dengue virus can experience a range of symptoms from none to a severe, potentially life-threatening illness. Most commonly, people with symptoms experience a rapid onset of fever with headache, pain behind the eyes, muscle and joint pains, flushing of the face, decreased appetite, abdominal pain and nausea. A red, flat rash over the entire body that develops within three to four days of the start of fever is also common. Severe dengue can lead to bleeding, organ failure and shock. In these rare, but severe, cases, early diagnosis and comprehensive medical care in an intensive care unit are critical for saving lives. 

Infection with one type of dengue does not provide immune protection against the others, so people can be infected up to four times throughout their life. Unfortunately, additional dengue infections increase a person’s risk of experiencing severe disease.

How do you catch dengue?

Dengue virus is found in the blood of infected people, and it is most often spread through the bite of a mosquito. Two parts of this process are helpful to understand:

• Infection of the mosquito — Two types of mosquitos are known to spread dengue virus: Aedes aegypti and Aedes albopictus. Female Aedes mosquitos bite people because they need human blood to produce eggs. When the mosquito ingests an infected person’s blood, it becomes infected with dengue virus. Once infected, the mosquito will remain infectious for the remainder of its life (up to four weeks).
• From mosquito to human — When infected, dengue virus can be found throughout a mosquito’s body, including in its salivary glands. This is important because mosquito saliva includes a chemical that prevents a person’s blood from clotting during the feeding process. As such, when an infected mosquito bites someone, they share not only their saliva but also dengue virus. After a person is exposed to the virus in the mosquito’s saliva, symptoms typically begin about five to seven days later.   

Dengue is transmitted in tropical and subtropical regions where these types of mosquitos commonly live. In the United States, dengue is most common in Puerto Rico, American Samoa, the U.S. Virgin Islands, the Federated States of Micronesia, the Republic of Marshall Islands and the Republic of Palau.

How common is dengue?

Because more than half of the world’s population lives in areas where dengue is common, each year about:

• 400 million people get infected.
• 100 million of those people experience symptoms.
• 40,000 people die from their infection.

While any dengue infection can lead to severe disease, the second infection is most likely to cause severe dengue because of a phenomenon known as “antibody-dependent enhancement” (ADE). In ADE, antibodies meant to protect against the dengue virus actually make it easier for the virus to enter cells and reproduce, resulting in a more severe infection than likely would have occurred otherwise.

The vaccine

Prevention measures have traditionally focused on controlling the mosquito population and using personal protective measures, like applying insect repellent, wearing long sleeves and pants, and using mosquito nets, especially in areas where the disease is common. While a vaccine is now available, it is only used for a very specific group. To get the dengue vaccine, one must meet three important criteria:

1. The individual must live in a high-risk area. Simply visiting the area is not sufficient to qualify someone for this vaccine.
2. They must be between 9 and 16 years of age.
3. They must have had a previous case of dengue that was confirmed by laboratory testing at the time of diagnosis or can be confirmed by a blood test prior to vaccination.

The reason for these strict criteria relate to aspects of both the disease and the vaccine. Specifically, as mentioned, a second infection with dengue tends to be more severe. This became an issue during the testing of earlier versions of dengue vaccine. Early vaccine studies showed that if a person was vaccinated before ever being infected with dengue, when they were eventually infected, their disease was more severe because of ADE. Studies of the current dengue vaccine showed that if a person had a dengue infection before vaccination, ADE did not occur after receipt of the vaccine or during any future dengue infections.

By choosing a group that was likely already infected with dengue, based on their age and where they live, and by confirming a previous infection, providers can ensure that the vaccine is given after a first infection but, hopefully, before a second one.

For those who qualify for vaccination, the vaccine is given as three doses with the second and third doses administered six and 12 months after the first dose, respectively. 

How is the dengue vaccine made?

Efforts to develop a dengue vaccine have been ongoing since the 1920s. It proved extremely challenging to make a vaccine effective against all four types of dengue virus. The vaccine used in the United States contains live, weakened yellow fever vaccine viruses that have been altered to include the parts of dengue virus against which we make an immune response. Each of the four virus types in the vaccine protect against one of the four types of dengue virus. The vaccine was approved in 2019.

Does the dengue vaccine work?

The vaccine has been shown to reduce the need for hospitalization in 8 of 10 recipients, and protective immunity lasts for at least six years and likely longer. This aspect continues to be monitored.

What are the side effects of the dengue vaccine?

A small number of people may experience mild side effects, like headache, pain at the site where the vaccine was given, tiredness, weakness and muscle aches in the first couple of days after vaccination.

Other questions you might have

Why is this vaccine given at specific ages?

Children younger than 9 years of age are less likely to have had a dengue infection. Because it is important to only give this vaccine after a first natural infection, younger children should not receive it. At this time, data are limited related to how well the vaccine works in people over 16 years of age. For these reasons, vaccination is limited to children between 9 and 16 years of age. 

Why is this vaccine only given to people who have had a prior dengue infection?

People who are vaccinated before their first natural infection are at increased risk of experiencing severe dengue if they are infected after vaccination. Therefore, it’s important that this vaccine only be given to people who are known to have been previously infected based on blood tests.

How can we know if our child had a previous dengue infection?

Children are evaluated for previous dengue infection using a blood test. Your healthcare provider will be aware of the testing options for children who live in areas where dengue is common and the vaccine is recommended. Talk to your child’s doctor if you have questions or concerns related to whether they need to be tested.

Should my child get this vaccine if we are traveling to an area where dengue exposure is possible? 

No. At this time, vaccination is only recommended for people who live in an area where dengue is common. It is not recommended for travelers.

Relative risks and benefits

Do the benefits of the dengue vaccine outweigh its risks?

The dengue vaccine can cause mild side effects. On the other hand, at least 100 million cases of symptomatic dengue disease occur throughout the world each year with about 40,000 deaths.

Disease risks

• Headache
• Pain behind the eyes
• Muscle and joint pain
• Flushing of the face
• Decreased appetite
• Abdominal pain
• Nausea
• Rash
• Hemorrhagic fever and shock, including bleeding and organ failure
• Death

Vaccine risks

If an individual has not previously been infected with dengue virus, vaccination can increase the risk of severe dengue disease during a post-vaccination infection. For this reason, it is critical to have had a documented dengue infection prior to being vaccinated. For those who have already been infected with dengue virus, this risk of severe disease following vaccination does not exist, so vaccine recipients may experience only minor side effects like:

• Headache
• Pain at the injection site
• Tiredness
• Weakness
• Muscle aches  

References

Orenstein W, Offit PA, Edwards KM and Plotkin SA. Dengue vaccines, in Vaccines, 8th Edition, 2024, 275-285.

American Academy of Pediatrics. Dengue. In: Kimberlin DW, Barnett ED, Lynfield R, Sawyer MH, eds. Red Book Online: 2021 Report of the Committee on Infectious Diseases. 32nd ed. American Academy of Pediatrics; 2021.

Centers for Disease Control and Prevention. Dengue Vaccine. December 16, 2021. Accessed Jan. 31, 2024.