Current vaccines might not protect against emerging Japanese encephalitis strain: study

Current vaccines may fail to protect individuals against an emerging strain of the Japanese encephalitis virus, the leading cause of viral encephalitis in Asia, Chinese researchers said Tuesday.

Japanese Encephalitis virus can be separated into five genotypes, namely G1 to G5. Strain G5 was originally isolated from a patient and described in 1951, but then not seen again until found in 2009 in China and subsequently in South Korea.

No specific treatment exists against the virus, but a number of vaccines are used to protect local populations and travelers. All of the vaccines are based on G3 virus strains and have been shown previously to work well against G1 through G4 strains.

In the new study, published in the U.S. journal PLOS Neglected Tropical Diseases, Guodong Liang and colleagues from the Chinese Center for Disease Control and Prevention compared G3 and G5 viruses and tested whether the vaccine commonly used in China can protect against G5 viruses.

They injected mice with the G3-based vaccine and found it protected all the mice against a lethal challenge with G3 virus, but only 50 percent of the mice infected with G5 virus survived.

Next, the researchers looked for inactivating antibodies in 26 vaccinated two-year-old children and were able to detect neutralizing antibodies against G3 strains in all the children, but only 35 percent of them also had antibodies that could neutralize G5 strains.

Finally, the researchers analyzed samples from 45 patients who had been infected with the virus naturally and found while all of the patients had neutralizing antibodies against G3 strains, only 29 of the 45 patients, or 64 percent, had the ability to neutralize G5 strains.

Most of the latter were older patients, while less than half of the patients under the age of 15 had neutralizing antibodies against G5 virus.

The results suggested that natural infection with a different strain might not protect against subsequent G5 infection, especially in children.

"Based on these results, we propose that the current JE (Japanese Encephalitis) vaccine derived from G3 JE virus (JEV) does not provide adequate levels of protection against the emerging G5 JEV genotype," they wrote in their paper.

"Our results demonstrate the need for more detailed studies to reevaluate whether or not the apparent emergence of G5 JEV can be attributed to failure of the current vaccine to induce appropriate immune protectivity against this genotype of JEV." Endit