People who have experienced severe dengue often describe it as feeling as though every bone in the body is breaking. The illness may involve a persistently high fever, intense headache, and overwhelming fatigue that makes getting out of bed difficult. Some patients develop bleeding or shock and require urgent hospitalization.
Dengue is common in Thailand and throughout Southeast Asia. It remains a major cause of illness and death among people of all ages, particularly children and individuals who have previously been infected, as a second infection with a different dengue virus type may carry a greater risk of severe disease.
This article provides a comprehensive overview of dengue, including its causes, symptoms, viral serotypes, currently available vaccines, and self-care measures that can help reduce the risk of infection and severe illness.
What Is Dengue and What Causes It?
Source and Mechanism of Infection
Dengue fever is caused by the dengue virus (DENV). Its principal vectors are the Aedes aegypti mosquito and, in some areas, the Aedes albopictus mosquito.
Transmission begins when an Aedes mosquito feeds on the blood of a person who has dengue virus circulating in their bloodstream. The virus enters and multiplies inside the mosquito. When the infected mosquito later bites another person, the virus is transmitted to that individual. Dengue does not spread directly from person to person and normally requires an infected mosquito as the vector.
Aedes mosquitoes commonly lay their eggs in stagnant water collected in containers such as plant saucers, old tires, uncovered water containers, or even small amounts of water trapped in folded plastic. Thailand’s warm and humid climate allows these mosquitoes to breed throughout the year. Dengue outbreaks usually increase during the rainy season, particularly from May to September, when more standing-water breeding sites are available.
Symptoms of Dengue
Dengue symptoms range from mild illness to severe, potentially life-threatening disease. The clinical course is generally divided into three phases.
Febrile Phase
During the first 2–7 days, patients typically develop a sudden high fever, often reaching 39–40°C, together with severe headache, pain behind the eyes, intense muscle and joint pain—sometimes giving dengue the name “breakbone fever”—nausea, vomiting, and occasionally a red skin rash.
Critical Phase
The critical phase commonly begins as the fever starts to subside, usually between days 3 and 7 of illness. In severe cases, plasma may leak from the blood vessels, leading to fluid accumulation in the abdomen or around the lungs.
Abnormal bleeding may also occur, including nosebleeds, bleeding gums, or small bleeding spots beneath the skin known as petechiae. Some patients may develop dengue shock syndrome, a life-threatening condition requiring immediate medical treatment.
Recovery Phase
During the final 2–3 days, most patients who have passed through the critical phase begin to recover. The body gradually reabsorbs the leaked fluid into the bloodstream, symptoms improve, and appetite usually returns.
Warning signs requiring immediate medical attention include severe abdominal pain, persistent vomiting, abnormal bleeding, rapid or difficult breathing, unusual drowsiness, cold hands or feet, or unexplained restlessness.
Dengue Virus Has Four Main Serotypes
Dengue virus is divided into four major serotypes: DENV-1, DENV-2, DENV-3, and DENV-4. Each serotype can cause dengue illness, and all four circulate in Thailand, with the predominant serotype varying from year to year.
Some studies have associated DENV-2 and DENV-3 with a greater likelihood of severe disease. However, dengue severity depends on several interacting factors, including the viral serotype, the patient’s immune response, and any history of previous dengue infection.
Summary Table: Four Dengue Virus Serotypes
| Serotype | Characteristics | Remarks |
|---|---|---|
| DENV-1 | Commonly circulates in tropical regions | Can cause disease of any severity |
| DENV-2 | Associated with severe illness in some cases | Frequently identified during large outbreaks |
| DENV-3 | Widely found in Asia and Africa | May cause severe disease during secondary infection |
| DENV-4 | Detected less frequently than other serotypes | Can still cause dengue illness and complications |
Can Someone Who Has Had Dengue Become Infected Again?
Yes. Reinfection is possible, and this is one of the features that makes dengue more complex than many other viral infections.
When a person becomes infected with one dengue serotype, the body develops long-term immunity specifically against that serotype. However, protection against the other three serotypes is only temporary. After approximately 2–3 months, this short-term cross-protection gradually declines, and the person may become infected with another dengue serotype.
Research has also shown that a second infection with a different serotype may carry a higher risk of severe illness because of an immune mechanism known as antibody-dependent enhancement (ADE). In some cases, antibodies remaining from the first infection may make it easier for a different dengue serotype to enter immune cells.
For this reason, people who have previously had dengue should not assume that they are fully protected. Dengue vaccination may be beneficial for some individuals, but eligibility should be assessed by a doctor based on each person’s age, medical history, and risk factors.
What Is the Dengue Vaccine?
Benefits and Scope of Protection
A dengue vaccine is a biological product designed to stimulate the immune system to recognize and fight dengue virus without causing severe dengue disease.
Potential benefits of dengue vaccination include:
- Reducing the risk of symptomatic dengue infection, particularly among people living in areas with high transmission
- Lowering the likelihood of severe complications, including abnormal bleeding, shock, and severe dengue
- Reducing the risk of hospitalization, thereby decreasing medical expenses and the impact of illness on quality of life
However, dengue vaccines do not provide 100% protection. Vaccinated individuals should continue to prevent mosquito bites and reduce mosquito breeding sites. Dengue vaccines also have specific indications, limitations, and precautions that differ considerably from many routine vaccines. A medical assessment is therefore required before vaccination.
Which Dengue Serotypes Do the Vaccines Cover?
Most currently developed dengue vaccines are tetravalent, meaning that they are designed to provide protection against all four dengue virus serotypes: DENV-1, DENV-2, DENV-3, and DENV-4. This approach aims to reduce the risk of infection regardless of which serotype is circulating in the community.
TAK-003, marketed as Qdenga, is a tetravalent dengue vaccine recognized by the World Health Organization and approved by regulatory authorities in several countries, including the Thai Food and Drug Administration. The WHO identifies TAK-003 as the second dengue vaccine recommended for use in selected population groups.
What Types of Dengue Vaccines Are Currently Available?
Comparison Table: Current Dengue Vaccines
| Vaccine | Serotypes Covered | Number of Doses | Recommended Age Range | Important Considerations |
|---|---|---|---|---|
| Qdenga (TAK-003) | DENV 1-4 | 2 doses, 3 months apart | 4-60 years under Thai FDA approval | WHO recommends programmatic use for children aged 6-16 years in high-transmission settings |
| Dengvaxia (CYD-TDV) | DENV 1-4 | 3 doses, given 6 months apart | Highly restricted eligibility | U.S. FDA approval is limited to individuals with laboratory-confirmed previous dengue infection |
Tetravalent Dengue Vaccine
A tetravalent dengue vaccine is designed to stimulate immunity against all four dengue serotypes simultaneously: DENV-1, DENV-2, DENV-3, and DENV-4. Its main purpose is to reduce the risk of dengue infection from any circulating serotype and lower the likelihood of severe disease among vaccinated individuals.
Qdenga Vaccine (TAK-003)
Qdenga, also known as TAK-003, is a live attenuated tetravalent dengue vaccine developed by Takeda Pharmaceutical Company.
The vaccine uses an attenuated form of DENV-2 as its genetic backbone. Components from DENV-1, DENV-3, and DENV-4 are incorporated so that the immune system can develop responses against all four dengue serotypes.
According to product information registered with the Thai FDA, Qdenga is indicated for the prevention of dengue caused by any dengue virus serotype in individuals aged 4–60 years. The WHO recommends programmatic use of TAK-003 primarily for children aged 6–16 years in settings with high dengue transmission. Nevertheless, vaccination should follow the advice of a doctor and the official recommendations applicable in each country.
Dengvaxia Vaccine (CYD-TDV)
Dengvaxia, or CYD-TDV, is another tetravalent dengue vaccine developed by Sanofi Pasteur. Its use is subject to substantially greater restrictions than Qdenga.
According to the U.S. Food and Drug Administration, Dengvaxia is approved only for individuals aged 9–16 years who live in dengue-endemic areas and have laboratory-confirmed evidence of a previous dengue infection.
This restriction exists because studies found that people who had never previously been infected with dengue, known as seronegative individuals, could face a higher risk of severe dengue if they received Dengvaxia and were later naturally infected. Confirming previous dengue infection is therefore essential before this vaccine is administered.
The Number of Doses Depends on the Vaccine Type
Each dengue vaccine has a different dosing schedule, as follows:
- Qdenga (TAK-003): Two doses, with the second dose administered approximately three months, or 12 weeks, after the first dose.
- Dengvaxia (CYD-TDV): Three doses, with each dose administered six months apart.
Patients should understand that dengue vaccination is not completed with a single injection. Every scheduled dose should be received according to the appointment arranged by the doctor so that the immune system can develop the most effective level of protection.
Complete Every Dose According to Schedule for Optimal Protection
Failing to complete the recommended schedule may result in an inadequate immune response. Patients should record each vaccination date in their personal health record or arrange the next appointment with their doctor in advance.
If a scheduled dose must be postponed, the patient should inform the doctor so that the appropriate timing for the remaining dose can be assessed. The doctor will determine whether the vaccination series can be continued or whether any adjustment is required.
Who Should Consider Receiving the Dengue Vaccine?
People Living in Areas with Frequent Dengue Outbreaks
Individuals who live in areas where dengue cases are frequently reported, or in communities with naturally high populations of Aedes mosquitoes, have a greater risk of infection than those living in areas with lower transmission.
For these individuals, consulting a doctor about dengue vaccination may be a worthwhile option for reducing risk. This may be particularly relevant for people living in rural or semi-rural areas where natural sources of standing water are common.
People Who Have Previously Had Dengue
Individuals with a history of dengue infection may face a greater risk of severe illness if they are later infected with a different dengue virus serotype. Certain vaccines may help reduce this risk.
However, a doctor should always assess the patient’s previous infection history, age, overall health, and the most appropriate vaccine type before vaccination.
Long-term study data for Qdenga suggest that the vaccine provides beneficial protection in both individuals who have and have not previously had dengue. Nevertheless, vaccination should always follow current medical guidance and the latest official recommendations.
Children, Adolescents, and Adults Within the Approved Age Range
Each dengue vaccine has a different approved or recommended age range. For example, product information registered with the Thai Food and Drug Administration indicates that Qdenga is approved for individuals aged 4–60 years.
The World Health Organization, however, recommends programmatic use primarily for children aged 6–16 years in areas with high dengue transmission.
Because recommendations may differ between regulatory authorities and public health organizations, individuals interested in vaccination should consult a doctor directly for advice suited to their age, medical condition, and personal risk.
