Why do people still get Japanese encephalitis after 4 doses of vaccine?

On June 16, the Hanoi Department of Health recorded the first case of Japanese encephalitis of the year, a 12-year-old boy in Phuc Tho district. The boy had received four doses of vaccine, the last of which was on June 15, 2019.

Explaining why children who have been vaccinated still get sick, a representative of the Hanoi Center for Disease Control (CDC) said that according to the Ministry of Health's instructions, to prevent Japanese encephalitis, children need to receive 3 basic doses, including: 1st dose when the child is 12 months old; 2nd dose: 1-2 weeks after the 1st dose; 3rd dose: 1 year after the 2nd dose. Then repeat every 3-5 years until the child is 15 years old.

"This boy received his last injection in June 2019. According to the recommendation, he should receive another injection every 3-4 years. However, this child did not receive a booster shot and thus contracted the disease. However, when children receive the basic injections, the severity of the disease will be largely reduced," said a representative of the Hanoi CDC.

Dr. Pham Quang Thai, Head of the Northern Expanded Immunization Office, National Institute of Hygiene and Epidemiology, said there are many reasons why a person who is vaccinated still gets sick, such as the immune system gradually decreasing over time, the individual's constitution, or the virus's attack dose.

In particular, the effectiveness of the vaccine cannot provide 100% absolute protection, on average 90-95% depending on the type, so a small number of children who have been vaccinated can still get the disease. In this case, the vaccine only protects for about 3-4 years, so the manufacturer recommends a booster shot, not because of the quality of the vaccine.

"The value of vaccines in preventing disease cannot be denied. In case of unfortunate illness, vaccines can also help to make symptoms milder and reduce the severity of the disease," said Dr. Thai, recommending that everyone should follow the full vaccination schedule, including booster shots.

The Hanoi CDC assessed that the rate of children in the expanded immunization age group who have been fully vaccinated is always high. "This boy is just an isolated case, and does not pose any problem for the vaccination campaign," said a CDC representative.

Japanese encephalitis is an acute blood-borne disease caused by the Japanese encephalitis virus. In Vietnam, Culex tritaeniorhynchus mosquitoes breed strongly in the summer (especially from March to July), and are active at dusk. This mosquito species has a high density in the plains and midlands, and is the main vector of Japanese encephalitis in our country.

The disease often causes encephalitis and meningitis in children, with a high mortality rate and sequelae (25-35%). Japanese encephalitis is often difficult to detect early because the initial symptoms are very similar to other infections. On the second or third day of the disease, symptoms gradually become more obvious, such as sudden high fever, nausea, vomiting, headache, lethargy, and slow response.

According to the latest vaccination schedule updated by the Ministry of Health, there are currently 11 infectious diseases that require vaccines in the expanded immunization program, including Japanese encephalitis B.