The vaccine contains a live weakened form of the chikungunya virus and is designed to be administered in a single dose via muscle injection. The vaccine is sufficiently weakened to prevent disease while stimulating an immune response in recipients. Its safety profile was evaluated through clinical studies in North America, involving approximately 3,500 participants. The most common side effects were found to be mild headache, fatigue, muscle pain, joint pain, fever, nausea, and injection site tenderness, However, there were instances of severe chikungunya-like symptoms in 1.6% of vaccine recipients.

Chikungunya, derived from the Makonde language of Tanzania meaning “to become contorted”, describes the debilitating joint pain the virus causes. Initially identified in Tanzania in 1952, the virus has spread globally, affecting over 110 countries in Asia, Africa, Europe, and the Americas.

The virus is transmitted by Aedes aegypti and Aedes albopictus mosquitoes, which also spread dengue and Zika viruses. These mosquitoes breed in standing water and are primarily active during daylight hours. Humans serve as the primary reservoir for the virus, facilitating its spread when a mosquito bites an infected person and then transmits it to others. Mosquito control is a crucial aspect of managing the disease. Prevention also involves avoiding mosquito bites.

The transmission cycle involves an uninfected mosquito feeding on an infected person and then transmitting the virus to new hosts. Symptoms typically appear 4–8 days after infection. Chikungunya's hallmark is intense joint pain, often leading to a stooped posture in affected individuals. Other symptoms include muscle pain, headache, nausea, and rashes. Children, however, may exhibit milder or no symptoms. Although most patients recover, joint pain can persist, requiring pain relief and anti-inflammatory therapy. Reinfection is rare, as the disease appears to confer lasting immunity.

Diagnosis during the first week of illness can be achieved using reverse transcription–polymerase chain reaction (RT–PCR), while antibody detection tests are used after the first week. Confirmatory tests can help to distinguish it from dengue. Most patients recover fully, but severe cases can lead to eye, heart, and neurological complications, with newborns and the elderly at greatest risk.

The first chikungunya outbreaks in India occurred in 1963, 1965, and 1973, with sporadic cases continuing in the next century. Then, chikungunya dramatically re-emerged in 2005-2006 (as part of a broader global trend), thirty-five years after its last major outbreak!

The increased frequency and extent of outbreaks since 2004 are partly due to viral adaptations that enhance its transmission by the Aedes albopictus mosquito. Climate change will also expand the range of mosquitoes that harbour the virus, bringing infections to places that have never had major outbreaks before.

According to the National Centre for Vector Borne Disease Control, there were 57,813 suspected and 9,756 confirmed cases of chikungunya in India in 2018. In 2022, there were 148,587 suspected and 8,067 confirmed cases of chikungunya. Based on provisional data through the middle of September, there will likely be more than 100,000 suspected cases this year, with confirmed cases ranging in the thousands. A more detailed analysis of the data shows very wide ranges in numbers reported by state, perhaps indicating variance in prevalence. The fluctuations could also be due to differences in testing and reporting from each state.

What is undeniable is that chikungunya continues to be a public health concern in India and that the country will benefit from the distribution of a vaccine that could prevent this mosquito-spread viral disease.

The approval of the Valneva vaccine bodes well for the many other chikungunya vaccine candidates at various stages of clinical trials. In India, Bharat Biotech may be close to a breakthrough with its inactivated virus candidate for chikungunya. This vaccine, which will be administered in two doses, was in advanced clinical trials as of late August. All in all, it is a time to hope for a safe and effective chikungunya vaccine that will be widely available in India to prevent this debilitating, modern disease.

Anirban Mahapatra is a scientist by training and the author of COVID-19: Separating Fact From Fiction. He is currently finishing up his second popular science book. The views expressed are personal