Smitha (name changed), a resident of Attingal, had had a full course of anti-rabies vaccination when six months ago, she was bitten by a stray dog. But a few weeks ago, when she again sustained a dog bite, doctors advised her that she did not need a full course of antirabies vaccination again and that just a booster dose was sufficient.
She was warned that taking two full courses of anti rabies vaccinations so close in time can lead to hyperimmune reactions.
However, Smitha was not convinced. Scared by reports of how people developed rabies despite getting vaccinated, she insisted that she be given the full course of vaccination again.
“We suggested that she send a blood sample to us so that we can study the seroconversion levels against rabies from the vaccination she had earlier (seroconversion is the development of specific antibodies in blood in response to an infection or vaccination). According to the World Health Organisation, rabies virus-neutralizing antibody titre of 0.5 IU/mL or above is considered as an adequate immune response after vaccination. The blood sample had an antibody titre of 16 IU/ml, which was clear proof that she need not take the full course of anti rabies vaccination,” says E. Sreekumar, Director of the Institute of Advanced Virology here.
One of the key requirements of successful vaccination against rabies is the induction of a robust neutralizing antibody response against glycoprotein G, a key viral protein that facilitates the virus infection. The level of antibodies against the protein is considered as a surrogate marker of protection against rabies. These virus neutralizing antibodies protect against rabies by blocking viral entry into host cells.
The current gold standard techniques being used to estimate virus neutralising antibodies are rapid fluorescent focus inhibition test (RFFIT) and fluorescent antibody virus neutralization test (FAVN). Both tests require handling of live rabies virus in stringent biosafety conditions and vaccinated laboratory personnel to perform the tests
IAV has now developed a simple alternative assay for detecting neutralising antibodies against rabies virus in vaccinated humans as well as animals which use pseudoviruses for evaluating the immune response generated by vaccines.
Pseudoviruses are much safer to use in a laboratory setting due to their restricted infectivity and lack of virulent viral components
IAV had in April this year reported the development of a vesicular stomatitis virus (VSV)-based pseudovirus assay, which showed comparable performance to RFFIT assay, for evaluating immune response against rabies vaccine in humans (Lupitha et al., 2025; https://doi.org/10.1371/journal.pntd.0013010 ).
The use of this same assay was extended by IAV recently for efficacy analysis of animal rabies vaccination and it proved to be successful too (https://doi.org/10.1016/j.vetimm.2025.111026).
“Both RFFIT and FAVN tests for analysing seroconversion against rabies vaccines have limitations for large-scale use due to the need for higher bio-containments, low-throughput and a high cost. The assays we have developed are simpler, have a high throughput and can be used for large-scale immune response surveillance studies, especially in rabies endemic areas,” says Dr. Sreekumar.
There were at least three cases of human rabies in the State last year, wherein vaccinated children had developed rabies later, following which the efficacy of rabies vaccination had been called into question.
The assay developed by IAV would be useful in ensuring that anti rabies vaccination has generated protective levels of antibodies, especially in high risk groups such as animal handlers, forest officials, pet owners and veterinarians, who interact with animals daily as part of their occupation.
“Many people tend to ignore bites from their pets, believing that their pet is protected against rabies through vaccination. But with veterinary vaccines, we often may not be sure if cold chain maintenance was proper, whicch could affect the efficacy of the vaccine. This test is one way to ensure that your vaccinated pets do have protective immunity against rabies,” Dr. Sreekumar says.
IAV’s effort is to expand public health accessibility to anti-rabies antibody testing to ensure efficacy of rabies immunisation, thereby contributing to global rabies control and elimination. The test is being offered to public at ₹500/sample
Published – November 22, 2025 06:35 pm IST
