Chikungunya Vaccine - A Promising Outlook for the Future

Introduction

Southern Tanzania witnessed chikungunya disease first in the year 1952, and since then, there have been several outbreaks, and it is now identified in 110 countries. The year 2023 witnessed a surge in the number of cases and fatalities associated with chikungunya in the region of the United States of America. Multiple countries and regions experienced outbreaks of chikungunya, including areas where local transmission had not been previously recorded. Furthermore, there was a notable rise in the number of cases among newborns and a higher incidence of severe cases among the elderly. Additionally, the case fatality rate (CFR) also showed an increase compared to previous years.

What Is Chikungunya Disease?

Chikungunya is an RNA-virus disease transmitted to humans by infected mosquitoes, primarily the Aedes egypti and the Aedes albopictus species. Within four to seven days of the bite from an infected mosquito, individuals usually develop symptoms. It is characterized by symptoms such as fever, generalized body pain, joint pain, headaches, muscle aches, rashes, and overall tiredness. Symptoms usually last two or three days, and most individuals recover without further health complications. However, some individuals experience prolonged joint pain. Although rare, cases of neurological, gastrointestinal, heart, and eye complications have been reported. Chikungunya can be diagnosed through laboratory tests that detect the presence of the virus or specific antibodies in an individual's blood sample.

Currently, antiviral drugs specific to chikungunya disease are not available. Treatment measures mainly involve providing the individual with symptomatic relief. Medications such as Acetaminophen and Paracetamol are usually prescribed to help alleviate pain and for fever management. A clean environment plays a vital role in preventing infectious diseases. Chikungunya could be prevented by practicing measures to prevent the breeding of mosquitoes. The use of insecticides can help prevent the same. One may also wear covered clothing and use mosquito repellents in areas prevalent with mosquitoes to minimize mosquito bites. At present, there are no vaccinations available against Chikungunya virus. However, several vaccination trials were ongoing, and a recent trial has shown promising results.

What Is the New Chikungunya Vaccine?

VLA1553 is an experimental vaccine candidate that aims to protect against Chikungunya virus infection. It is a single-dose (1 × 104 TCID50 per 0.5 milliliters) vaccine made from a weakened form of the virus, designed to target all known strains, including the rapidly spreading strain. The vaccine is developed using a modified version of the La Reunion strain of the Chikungunya virus, which is designed to be less harmful but still be able to stimulate a long-lasting, strong immune response in individuals.

How Was the Chikungunya Vaccine Study Done?

• Four thousand hundred fifteen healthy individuals were chosen for the study from the United States of America across forty-three different study sites.

• A single dose of VLA 1553 was injected into the arm of three thousand eighty-two individuals, and a placebo was given to the remaining one thousand thirty-three individuals.

• Safety analysis was done for all the individuals involved in the study. The trial then divided the individuals into a smaller sub-group of three hundred sixty-two individuals to test for the immune response.

• Vaccination was given to two hundred sixty-six individuals, and a placebo was given to the remaining ninety-six individuals.

• The adverse effects of the vaccine were recorded electronically for eleven days. Assessment and observation of the immune response by the individuals were first done after one week of administering the vaccination.

• Similar assessments were then done twenty-eight days later and three months after vaccination. A final immune response assessment was done six months after the vaccination.

• Individuals were closely monitored for adverse effects.

What Were the Observations From the Chikungunya Vaccine Clinical Trial?

In the trial, the observations of the chikungunya vaccine (VLA1153) included the following:

• The vaccine effectively stimulated the immune system to produce antibodies against the Chikungunya virus.

• After twenty eight days of receiving a single-dose VLA1553, two hundred sixty three individuals of the trial developed Chikungunya virus-neutralizing antibodies. This shows that the vaccine successfully could induce the production of antibodies targeting the Chikungunya virus.

• These antibodies were present in the body for a considerable period (six months in 96 percent of individuals), providing ongoing protection against the virus.

• The vaccine showed consistent antibody generation across different age groups, suggesting that its effectiveness was not affected by the individual’s age.

• The observations were supported by a confidence interval (gives an idea of the precision of the results and how reliable the results are) of 95 percent.

• Forty-six individuals out of the entire trial did experience some adverse effects, including fever, pain in the joints and the back, rashes, swelling, and even neurological and cardiac problems were closely monitored. These adverse effects were observed within twenty-one days of vaccination, and all individuals recovered well without any further complications.

• Unfortunately, the rate of miscarriages observed in pregnant women of the trial group of VLA1553 was slightly higher than anticipated. However, this could also be due to the small sample size and natural variations accepted in studies of such sample sizes.

• However, the Data Safety Monitoring Board did not find any significant risk associated with the vaccination.

What Are the Limitations of the Chikungunya Vaccination Trial?

The study has some limitations, according to the authors involved in the study. These limitations include:

• The clinical trial was not done in an area where chikungunya was commonly found, and hence the study could not determine existing immunity to the virus in individuals involved in the trial.

• The safety of the chikungunya vaccination in this particular population remains uncertain.

• The vaccine is made from a weakened form of the live virus, which may not be suitable for pregnant women or individuals with weakened immune systems.

• To prevent and control the disease in endemic areas, the vaccine will need to be given to children as well. However, there is an ongoing study in Brazil (endemic areas) involving adolescents to assess the effectiveness of younger age groups.

Conclusion

Having a live-attenuated vaccine like VLA1553 that provides good antibody persistence after vaccination is crucial due to the unpredictable nature of the disease’s spread. Although further studies are needed to assess the effectiveness of VLA1553 in adolescents and pregnant women and its impact in the real world, the vaccine is expected to contribute significantly to being well-prepared against a probable future chikungunya outbreak.