The disease

What is dengue?

Dengue is an infection caused by four closely related viruses, referred to as dengue virus types 1-4. Certain mosquitoes carry these viruses. When an infected mosquito bites a person, the person can become infected. 

The four dengue viruses are part of the flaviviridae family. They are closely related to other viruses that are carried by ticks or mosquitoes and cause disease in people, 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:

• Rapid onset of fever with headache
• Pain behind the eyes
• Muscle and joint pain
• Redness or darkness and warmth of the face, called flushing
• Lack of 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 

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, with each dengue infection, the person’s risk of experiencing severe disease increases.

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 mosquitoes are known to spread dengue virus: Aedes aegypti and Aedes albopictus. Female Aedes mosquitoes 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 mosquitoes commonly live. In the U.S, dengue is most common in:

• Puerto Rico
• American Samoa
• U.S. Virgin Islands
• Federated States of Micronesia
• Republic of Marshall Islands 
• Republic of Palau

How common is dengue?

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 in areas where the disease is common, like:

• Applying insect repellent
• Wearing long sleeves and pants
• Using mosquito nets 

When the dengue vaccine was available, it was only used for a very specific group. To get the dengue vaccine, a person had to meet three important criteria:

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

The reasons 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 because of ADE. 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. The severity of the infection after vaccination was similar to the issue with the disease related to ADE. Studies of the dengue vaccine used in the U.S. 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 could ensure that the vaccine was given after a first infection but, hopefully, before a second one.

For those who qualified for vaccination, the vaccine was given as three doses that took a year to complete. The second dose was given six months after the first dose, and the third dose was given 12 months after the first dose. 

How was the dengue vaccine made?

Efforts to develop a dengue vaccine have been ongoing since the 1920s. It was extremely challenging to make a vaccine that protected against all four types of dengue virus. The vaccine that was used in the U.S. contained live, weakened yellow fever vaccine viruses that had 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 protected against one of the four types of dengue virus. The vaccine was approved in 2019 and withdrawn in 2025 due to low demand. The final doses could be used until they expired, which would occur in late 2026. 

Did the dengue vaccine work?

The vaccine reduced the need for hospitalization in 8 of 10 recipients. Protective immunity lasted for at least six years and likely longer.

In other countries, a different vaccine, called Qdenga, was preferred because it protected a similar number of people after only two doses separated by three months, and people did not need to be tested for a previous dengue infection. This vaccine has not been licensed in the U.S.

What were the side effects of the dengue vaccine?

A small number of people experienced mild side effects, like:

• Headache
• Pain at the site where the vaccine was given
• Tiredness
• Weakness 
• Muscle aches 

These side effects occurred in the first couple of days after vaccination.

Other questions you might have

Why was this vaccine given at specific ages?

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

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

People who got the Dengvaxia vaccine before their first natural infection were at increased risk of experiencing severe disease if they were infected after vaccination. This effect was found in the Philippines when some children who participated in early clinical trials were hospitalized with dengue and some died. When scientists evaluated what was happening, they found that the affected children had never been infected with dengue virus before they were vaccinated. Children who had a dengue infection before they got the vaccine did not have the same risk for severe infection and hospitalization. Therefore, it was important that this vaccine only be given to people with previous dengue infections confirmed by blood tests.

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

Children can be evaluated for previous dengue infection using a blood test. Healthcare providers in areas where dengue is common are aware of the testing options, and when the vaccine was available, they were aware that testing had to be completed before vaccination. If you have questions or concerns, talk to your child’s healthcare provider.

Should people traveling to an area where dengue exposure is possible be vaccinated? 

No. Even when a dengue vaccine was available in the U.S., vaccination was only recommended for people living in an area where dengue was common. It was not recommended for travelers.

Relative risks and benefits

Do the benefits of the dengue vaccine outweigh its risks?

In 2026, the last doses of dengue vaccine are only available in very limited areas of the U.S. Since the dosing schedule took one year to complete, only people who have already started the series are able to get any remaining doses. For most people in the U.S. vaccination against dengue virus is not currently an option.

References

Orenstein WA, Offit PA, Edwards KM and Plotkin SA. Dengue Vaccines in Plotkin's 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.

Carlson R. Dengue vaccines. March 1, 2026. Accessed March 18, 2026.

Reviewed by Paul A. Offit, MD, on March 18, 2026