Dengue Vaccine - All You Need to Know

Introduction

Dengue fever, caused by the dengue virus, is a significant public health concern in many parts of the world. With no specific antiviral treatment available, prevention remains the key strategy to combat this mosquito-borne illness. In recent years, developing and approving a dengue vaccine has shown promise in reducing the disease's impact. This article delves into dengue prevention through vaccination, exploring its benefits, limitations, and implications for public health.

What Is Dengue Fever?

Dengue, also known as break-bone fever, is a viral infection transmitted by mosquitoes to humans, particularly in tropical and subtropical regions. While many individuals afflicted with dengue may remain asymptomatic, those who experience symptoms typically encounter a high fever, headaches, body aches, nausea, and a rash. Most cases resolve within one to three weeks, yet severe dengue can necessitate hospitalization. In dire instances, dengue can prove fatal. To reduce the risk of infection, it is advised to avoid mosquito bites, especially during the daytime.

Presently, there is no specific treatment for dengue, and symptom management involves pain relief. Symptoms generally manifest four to ten days following infection. They may endure for two to seven days, featuring high fever, intense headache, eye pain, joint and muscle aches, nausea, vomiting, swollen glands, and a rash. Individuals encountering a second infection are at heightened risk of severe dengue. Often, severe symptoms emerge after the fever subsides, encompassing abdominal pain, persistent vomiting, rapid breathing, bleeding gums or nose, fatigue, restlessness, blood in vomit or stool, thirst, pale and cold skin, and weakness. Individuals experiencing these severe symptoms require immediate medical attention. After recovery, lingering fatigue might persist for several weeks in individuals who have contracted dengue.

Who Should Receive the Dengue Vaccine?

The CDC suggests that the dengue vaccine is appropriate for children aged 9 to 16, provided they have a history of prior dengue infection and reside in regions where dengue is prevalent. Verification of this past infection through laboratory testing is essential. Distinguishing itself from other vaccines, this particular vaccine is exclusively recommended for individuals who have previously encountered the dengue virus. This stipulation is because children lacking a history of dengue infection face an elevated risk of severe dengue illness and hospitalization if they contract dengue post-vaccination with Dengvaxia. Hence, healthcare professionals should ascertain evidence of a laboratory-confirmed earlier dengue infection before administering the vaccine.

Which Type of Dengue Vaccine Is Available?

Dengvaxia, scientifically known as CYD-TDV, stands as a tetravalent vaccine meticulously crafted to shield against the quartet of dengue virus serotypes. Its target audience encompasses individuals aged 9 to 45 residing in regions endemic to dengue. Dengvaxia vaccine providers administer three subcutaneous doses, each spaced six months apart (at zero, six, and 12 months) to achieve complete protection.

Operating on the principle of immunostimulation, the vaccine prompts the immune system to generate a defensive reaction against the virus, effectively diminishing the likelihood of experiencing severe illness following infection. Ongoing research is enhancing the understanding of the vaccine's duration of protection in children. As of now, it is established that the vaccine can safeguard against dengue for a minimum of six years.

Who Should Avoid the Dengue Vaccine?

The vaccine is not suitable for:

• Children under nine years old are less likely to have had prior dengue infection.

• Individuals over 16 years old, due to insufficient data on vaccine efficacy in this age group.

• Children without a history of prior dengue infection.

• Children with weakened immune systems (immunocompromised).

• Those who experienced severe allergic reactions to a previous vaccine dose or any ingredient.

• Individuals who have a severe allergy to any component of the vaccine.

• Travelers and non-residents of dengue-prone areas, as the vaccine is not approved for travel use by the FDA (Food and Drug Administration).

What Are the Potential Side Effects of the Dengue Vaccine?

1. For Children Who Have Previously Had Dengue:

• The most common side effects may include soreness, itching, pain at the injection site, headaches, fatigue, and overall discomfort. These reactions are typical indications that the body is developing protection and usually resolve within a few days.

• It's worth noting that some individuals might experience fainting after medical procedures, including vaccination. If feeling dizzy, noticing vision changes, or hearing ringing in the ears, inform the healthcare provider.

• Like any medication, there exists a highly remote possibility of the vaccine triggering a severe allergic reaction, other significant harm, or even death.

2. Potential Issues Following Any Vaccination:

• Fainting can sometimes occur after medical procedures, including vaccination. To prevent fainting and fall-related injuries, sitting or lying down for around 15 minutes after vaccination is advisable. Let the provider know if you are experiencing dizziness, vision alterations, or ear ringing.

• Like any medication, there is a scarce chance of a vaccine causing a severe allergic reaction, other severe complications, or fatality.

What Are the Current Developments in Dengue Vaccines?

The quest for effective dengue vaccines began in 1929, yet challenges persist due to the virus's complexity and the risk of immune-enhanced disease. A tetravalent vaccine, aiming for protection across all serotypes, has emerged as a critical solution. Despite a limited understanding of severe dengue's mechanisms and a lack of suitable animal models, recent years have seen substantial progress in vaccine development. Safety concerns, particularly immune-enhanced disease after vaccination, are carefully addressed through tetravalent vaccines that induce balanced immune responses. While numerous dengue vaccine candidates have entered clinical trials, one has reached phase III. This exemplifies the promising landscape of dengue vaccine development efforts.

• Live Attenuated Virus: Initial live attenuated dengue vaccine efforts involved serial passage of the virus in a nonhuman host but faced challenges during clinical trials due to incomplete seroconversion and reactogenicity. Subsequent work also encountered immunogenicity and reactogenicity concerns. Despite these hurdles, new formulations are promising in phase II studies, although further evaluation is necessary to determine protective efficacy and optimal dosing. The US National Institutes of Health introduced mutagenesis technology to alter dengue genomes genetically, resulting in attenuated variants for testing in flavivirus-naïve adults. Additionally, the US Food and Drug Administration developed a molecularly attenuated tetravalent dengue vaccine tested in nonhuman primates. Both approaches offer alternative paths toward constructing a live attenuated tetravalent dengue vaccine.

• Chimeric Virus Approach: The CDC (Centers for Disease Control and Prevention) devised a tetravalent chimeric dengue vaccine by incorporating DNA from the attenuated component of the live attenuated dengue virus vaccine. This tetravalent dengue chimeric vaccine candidate was then progressing through clinical testing. Another avenue involved inserting dengue structural genes into the infectious DNA of the established yellow fever vaccine virus strain lead candidate dengue vaccine displayed immunogenicity for all four serotypes and progressed to phase III efficacy trials. Enhanced disease caused by vaccine virus or vector transmission by recipients has not been observed. Molecular clone-based strategies offer benefits over traditional attenuation, including reduced risk of adventitious agents and enhanced quality assurance. When multiple dengue viruses are inoculated in human volunteers, interference requires study in genetically modified vaccine viruses.

• Inactivated Virus Approach: Inactivated whole virus vaccines possess the advantage of preventing pathogenic reversion and avoiding interference between combined vaccines. They demonstrate the ability to stimulate both cell-mediated and humoral immune responses. However, their limitation lies in expressing only the viral genome's structural proteins. This can produce antibodies that may not offer complete protection, potentially leading to breakthrough or enhanced infections. Adjuvants have been added to licensed vaccines to boost immunogenicity and are being explored.

• Subunit Vaccines: Recombinant subunit strategies offer benefits such as low reactogenicity and freedom from adventitious agents. Nevertheless, partial post-translational processing can yield protein variations from native forms, impacting antibody responses.

• DNA (Deoxyribonucleic Acid) Vaccines: Dengue DNA vaccines offer a potential path to trigger protective immunity while avoiding interference observed with multivalent live virus vaccines. A DENV-1 DNA vaccine exhibited neutralizing antibody development in volunteers receiving a high dosage. However, the DNA approach has risks, such as theoretical chromosomal DNA integration with potential gene impacts. Concerns of inducing autoimmune diseases like systemic lupus erythematosus through foreign DNA have not been validated in studies.

• Vectored Vaccines: Recombinant poxviruses and adenoviruses effectively elicit robust immune responses against diverse human pathogens, utilizing both humoral and cellular mechanisms. Various live virus vectors like adenovirus, alphavirus, and vaccinia virus have been modified to directly administer DENV E protein for dengue vaccine exploration. Additionally, yeast and insect cell-expressed recombination E proteins and virus-like particle-based dengue vaccine are also under preclinical examination.

Conclusion

Dengue virus triggers various clinical conditions, ranging from mild fever to severe DHF, posing a global health challenge. Vector control's impact on dengue transmission is constrained, and licensed antivirals for treatment are absent. A promising solution lies in developing a safe and potent dengue vaccine, which is expected to be the most efficient strategy for future dengue control. At present, the Dengvaxia dengue vaccine is the available in dengue-prone regions.