How many days does fever last after Japanese encephalitis vaccination?

In today’s society, every newborn child must receive vaccinations. Some children may develop fever after receiving the Japanese encephalitis (JE) vaccine. How many days does it typically take for this fever to subside?

How long does fever last after JE vaccination?

Generally, if the fever is solely a reaction to the vaccine, symptoms usually resolve within one to two days. This is because the JE vaccine induces only an immune response—not an actual disease state. Once administered, the vaccine stimulates the body’s immune system to produce antibodies, thereby conferring future protection against the Japanese encephalitis virus. Thus, this fever represents a normal immunological response rather than true illness. The vaccine contains inactivated (killed) JE virus particles—processed and non-infectious—so it cannot cause actual disease.

Typically, the fever lasts about one to two days, with body temperature rarely exceeding 38.5°C. If the child remains alert and in good spirits, providing ample warm water and light, easily digestible meals usually suffices to alleviate symptoms. However, some children may experience persistent fever above 38.5°C lasting longer than two days, or develop prominent clinical symptoms following JE vaccination. In such cases, the fever should not be attributed solely to vaccine reaction; instead, it may indicate a pre-existing underlying condition that was present prior to vaccination.

Vaccination may sometimes coincide with or exacerbate an existing illness—or even trigger a new one. In such instances, prompt medical evaluation at a hospital is essential. Treatment—including whether rapid fever reduction is appropriate—will depend on the specific diagnosis established through clinical assessment. Ensuring adequate rest and sufficient sleep is also important. We hope this information proves helpful!