There are no data on the use of inactivated Vero cell culture-derived Japanese encephalitis (JE) vaccine (JE-VC) as a booster among individuals who previously received inactivated mouse brain-derived JE vaccine (JE-MB).
Military personnel who received ≥3 doses of JE-MB or were JE vaccine-naïve were vaccinated with 2 doses of JE-VC on days 0 and 28. Serum neutralizing antibodies were measured pre-vaccination and 28 days after each dose. Non-inferiority was evaluated for seroprotection rate and geometric mean titer (GMT) between previously vaccinated participants post-dose 1 and vaccine-naïve participants post-dose 2.
Fifty-three previously vaccinated and 70 JE vaccine-naïve participants were enrolled. Previously vaccinated participants had significantly higher GMTs pre-vaccination, post-dose 1, and post-dose 2. Seroprotection rates among previously vaccinated participants post-dose 1 (44/44, 100%) were noninferior to those achieved in previously naïve participants post-dose 2 (53/57, 93%). The GMT was significantly higher in previously vaccinated participants post-dose 1 (GMT 315; 95% CI 191-520) compared to previously naïve participants post-dose 2 (GMT 79; 95% CI 54-114).
Among military personnel previously vaccinated with ≥3 doses of JE-MB, a single dose of JE-VC adequately boosts neutralizing antibody levels and provides at least short-term protection. Additional studies are needed to confirm these findings in other populations and determine the duration of protection following a single dose of JE-VC in prior recipients of JE-MB.
"The two vaccine types are derived from different JE virus (JEV) strains, SA14-14-2 and Nakayama, both of which, however, belong to the same JEV genotype (GIII). We  and others  have recently shown a significant cross-reactivity between the immune responses to these two vaccines: travelers primed with JE-MB do not require the regular two-dose schedule of JE-VC – one booster dose suffices to elicit protective levels of neutralizing antibodies. No data exist on the longevity of the response to such heterologous boost- ing. "
[Show abstract][Hide abstract] ABSTRACT: The inactivated Vero cell-derived vaccine (JE-VC, IXIARO) has replaced the traditional mouse brain-derived preparations (JE-MB) in travelers' vaccinations against Japanese encephalitis. We showed recently that a single JE-VC dose efficiently boosts immunity in JE-MB-primed vaccinees, and that JE-VC elicits cross-protective immunity against non-vaccine genotypes, including the emerging genotype I. While these studies only provided short-term data, the present investigation evaluates the longevity of seroprotection in the same volunteers.
The study comprised 48 travelers who had received (1) JE-VC primary series, (2) JE-MB primary series followed by a single JE-VC booster dose, or (3) JE-MB primary series and a single JE-MB booster dose. Serum samples were collected two years after the last vaccine dose, and evaluated with the plaque-reduction neutralization test against seven Japanese encephalitis virus strains representing genotypes I-IV. PRNT50 titers≥10 were considered protective.
Two years after the primary series with JE-VC, 87-93% of the vaccinees proved to be cross-protected against test strains representing genotypes II-IV and 73% against those of genotype I. After a single homologous or heterologous booster dose to JE-MB-primed subjects, the two-year seroprotection rates against genotype I-IV strains were 89-100%.
After JE-VC primary series, seroprotection appeared to wane first against genotype I. The first booster should not be delayed beyond two years. In JE-MB-primed subjects, a single JE-VC booster provided cross-protective immunity against genotype I-IV strains in almost all vaccinees, suggesting an interval of two years or even longer for the second booster. These data further support the use of a single JE-VC dose for boosting JE-MB immunity.
[Show abstract][Hide abstract] ABSTRACT: Illness in business travelers is associated with reduced productivity on the part of the employee as well as the employer. Immunizations offer a reliable method of preventing infectious diseases for international business travelers. The authors review the travel patterns of business travelers, available data on illnesses they encounter, their potential travel-associated risks for vaccine-preventable diseases and recommendations on immunizations for this population. Routine vaccines (e.g., measles, tetanus and influenza) should be reviewed to assure that they provide current coverage. The combined hepatitis A and hepatitis B vaccine with a rapid schedule offers options for those with time constraints. Other vaccine recommendations for business travelers need to focus on their destinations and activities and underlying health, taking into account the concept of cumulative risk for those with frequent travel, multiple trips or long stays.
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