Browsing by Author "Lars Lindquist"

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    Cross-protection elicited by primary and booster vaccinations against Japanese encephalitis: A two-year follow-up study
    (2013-12-17) Elina O. Erra; Helena Hervius Askling; Sutee Yoksan; Lars Rombo; Jukka Riutta; Sirkka Vene; Lars Lindquist; Olli Vapalahti; Anu Kantele; University of Helsinki Haartman Institute; Helsinki University Hospital; Karolinska Institutet; Mahidol University; Sormland County Council; Medical Centre Aava; Swedish Institute for Communicable Disease Control; Helsingin Yliopisto
    Background: 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. Methods: 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. PRNT50titers≥10 were considered protective. Results: 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%. Conclusions: 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. © 2013 The Authors.
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    Cross-protective capacity of Japanese encephalitis (JE) vaccines against circulating heterologous JE virus genotypes
    (2013-01-15) Elina O. Erra; Helena Hervius Askling; Sutee Yoksan; Lars Rombo; Jukka Riutta; Sirkka Vene; Lars Lindquist; Olli Vapalahti; Anu Kantele; University of Helsinki Haartman Institute; Helsinki University Hospital; Karolinska Institutet; Mahidol University; Sörmland County Council; Medical Centre Aava; Swedish Institute for Communicable Disease Control; Department of Veterinary Biosciences; Helsingin Yliopisto
    Current Japanese encephalitis vaccines are derived from strains of genotype III, yet heterologous genotypes are emerging in endemic areas. Inactivated vaccines given to European travelers were found to elicit protective levels of neutralizing antibodies against heterologous strains of genotypes I-IV. © 2012 The Author. Published by Oxford University Press on behalf of the Infectious Diseases Society of America.
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    A single dose of vero cell-derived Japanese encephalitis (JE) vaccine (ixiaro) effectively boosts immunity in travelers primed with mouse brain-derived JE vaccines
    (2012-09-01) Elina O. Erra; Helena Hervius Askling; Lars Rombo; Jukka Riutta; Sirkka Vene; Sutee Yoksan; Lars Lindquist; Sari H. Pakkanen; Eili Huhtamo; Olli Vapalahti; Anu Kantele; University of Helsinki Haartman Institute; Helsinki University Hospital; Karolinska Institutet; Sormland County Council; Travel Clinic; Swedish Institute for Communicable Disease Control; Mahidol University; Helsingin Yliopisto
    Background. A significant part of the world population lives in areas with endemic Japanese encephalitis (JE). For travelers from nonendemic countries, Vero cell-derived vaccine (JE-VC; Ixiaro) has replaced traditional mouse brain-derived vaccines (JE-MB) associated with safety concerns. The 2 vaccines are derived from different viral strains: JE-VC from the SA14-14-2 strain and JE-MB from the Nakayama strain. No data exist regarding whether JE-VC can be used to boost immunity after a primary series of JE-MB; therefore, a primary series of JE-VC has been recommended to all travelers regardless of previous vaccination history.Methods.One hundred twenty travelers were divided into 4 groups: Volunteers with no prior JE vaccination received primary immunization with (group 1) JE-MB or (group 2) JE-VC, and those primed with JE-MB received a single booster dose of (group 3) JE-MB or (group 4) JE-VC. Immune responses were tested before and 4-8 weeks after vaccination using plaque reduction neutralization test (PRNT) against both vaccine strains.Results.In vaccine-naive travelers, the vaccination response rate for test strains Nakayama and SA14-14-2 was 100 and 87 after primary vaccination with JE-MB and 87 and 94 after JE-VC, respectively. Antibody levels depended on the target virus, with higher titers against homologous than heterologous PRNT50 target strain (P < . 001). In travelers primed with JE-MB, vaccination response rates were 91 and 91, and 98 and 95 after a booster dose of JE-MB or JE-VC, respectively. Subgroup analysis revealed that a higher proportion of primed (98/95) than nonprimed (39/42) volunteers responded to a single dose of JE-VC (P < . 001).Conclusions.A single dose of JE-VC effectively boosted immunity in JE-MB-primed travelers. Current recommendations should be reevaluated. © 2012 The Author.
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    A single dose of vero cell-derived Japanese encephalitis (JE) vaccine (Ixiaro) effectively boosts immunity in travelers primed with mouse brain-derived JE vaccines.
    (2012-06) Elina O. Erra; Helena Hervius Askling; Lars Rombo; Jukka Riutta; Sirkka Vene; Sutee Yoksan; Lars Lindquist; Pakkanen, Sari H.; Eili Huhtamo; Olli Vapalahti; Anu Kantele; Mahidol University. Faculty of Medicine. Haartman Institute; Mahidol University. Institute of Molecular Bioscience
    BACKGROUND: A significant part of the world population lives in areas with endemic Japanese encephalitis (JE). For travelers from nonendemic countries, Vero cell-derived vaccine (JE-VC; Ixiaro) has replaced traditional mouse brain-derived vaccines (JE-MB) associated with safety concerns. The 2 vaccines are derived from different viral strains: JE-VC from the SA14-14-2 strain and JE-MB from the Nakayama strain. No data exist regarding whether JE-VC can be used to boost immunity after a primary series of JE-MB; therefore, a primary series of JE-VC has been recommended to all travelers regardless of previous vaccination history. METHODS: One hundred twenty travelers were divided into 4 groups: Volunteers with no prior JE vaccination received primary immunization with (group 1) JE-MB or (group 2) JE-VC, and those primed with JE-MB received a single booster dose of (group 3) JE-MB or (group 4) JE-VC. Immune responses were tested before and 4-8 weeks after vaccination using plaque reduction neutralization test (PRNT) against both vaccine strains. RESULTS: In vaccine-naive travelers, the vaccination response rate for test strains Nakayama and SA14-14-2 was 100% and 87% after primary vaccination with JE-MB and 87% and 94% after JE-VC, respectively. Antibody levels depended on the target virus, with higher titers against homologous than heterologous PRNT(50) target strain (P < .001). In travelers primed with JE-MB, vaccination response rates were 91% and 91%, and 98% and 95% after a booster dose of JE-MB or JE-VC, respectively. Subgroup analysis revealed that a higher proportion of primed (98%/95%) than nonprimed (39%/42%) volunteers responded to a single dose of JE-VC (P < .001). CONCLUSIONS: A single dose of JE-VC effectively boosted immunity in JE-MB-primed travelers. Current recommendations should be reevaluated. CLINICAL TRIALS REGISTRATION: NCT01386827.