Investigating the efficacy of monovalent and tetravalent dengue vaccine formulations against DENV-4 challenge in AG129 mice

Dengue (DEN) is the most important mosquito-borne viral disease, with a major impact on global health and economics, caused by four serologically and distinct viruses termed DENV-1 to DENV-4. Currently, there is no licensed vaccine to prevent DEN. We have developed a live attenuated tetravalent DENV vaccine candidate (TDV) (formally known as DENVax) that has shown promise in preclinical and clinical studies and elicits neutralizing antibody responses to all four DENVs. As these responses are lowest to DENV-4 we have used the AG129 mouse model to investigate the immunogenicity of monovalent TDV-4 or tetravalent TDV vaccines, and their efficacy against lethal DENV-4 challenge. Since the common backbone of TDV is based on an attenuated DENV-2 strain (TDV-2) we also tested the efficacy of TDV-2 against DENV-4 challenge. Single doses of the tetravalent or monovalent vaccines elicited neutralizing antibodies, anti-NS1 antibodies, and cellular responses to both envelope and nonstructural proteins. All vaccinated animals were protected against challenge at 60 days post-immunization, whereas all control animals died. Investigation of DENV-4 viremias post-challenge showed that only the control animals had high viremias on day 3 post-challenge, whereas vaccinated mice had no detectable viremia. Overall, these data highlight the excellent immunogenicity and efficacy profile of our candidate dengue vaccine in AG129 mice.     

Development of DENVax: a chimeric dengue-2 PDK-53-based tetravalent vaccine for protection against dengue fever

Dengue. virus infection is the leading arboviral cause of disease worldwide. A vaccine is being developed based on the attenuated DEN-2 virus, DEN-2 PDK-53. In this review, we summarize the characteristics of the parent DEN-2 PDK-53 strain as well as the chimeric viruses containing the prM and E genes of DEN-1, DEN-3 or DEN-4 virus in the genetic backbone of the DEN-2 PDK-53 virus (termed DENVax). Tetravalent DENVax formulations containing cloned, fully sequenced isolates of the DEN-2 PDK-53 virus and the three chimeras have been evaluated for safety and efficacy in preclinical animal models. Based on the safety, immunogenicity and efficacy in preclinical studies, Phase 1 clinical testing of DENVax has been initiated.     

Immunogenicity and protective efficacy of a vaxfectin-adjuvanted tetravalent dengue DNA vaccine

A prototype dengue-1 DNA vaccine was shown to be safe and immunogenic in a previous Phase 1 clinical trial. Anti-dengue-1 neutralizing antibody responses were detectable only in the group of volunteers receiving the high dose of nonadjuvanted vaccine and the antibody titers were low. Vaxfectin^®, a lipid-based adjuvant, enhances the immunogenicity of DNA vaccines. We conducted a nonhuman primate study to evaluate the effect of Vaxfectin^® on the immunogenicity of a tetravalent dengue DNA vaccine. Animals were immunized on days 0, 28 and 84, with each immunization consisting of 3 mg of Vaxfectin^®-adjuvanted tetravalent dengue DNA vaccine. The use of Vaxfectin^® resulted in a significant increase in anti-dengue neutralizing antibody responses against dengue-1, -3 and -4. There was little to no effect on T cell responses as measured by interferon gamma ELISPOT assay. Animals immunized with the Vaxfectin^®-formulated tetravalent DNA vaccine showed significant protection against live dengue-2 virus challenge compared to control animals (0.75 mean days of viremia vs 3.3 days). Animals vaccinated with nonadjuvanted DNA had a mean 2.0 days of viremia. These results support further evaluation of the Vaxfectin^®-adjuvanted tetravalent dengue DNA vaccine in a Phase 1 clinical trial.     

Development of a recombinant tetravalent dengue virus vaccine: Immunogenicity and efficacy studies in mice and monkeys

Truncated recombinant dengue virus envelope protein subunits (80E) are efficiently expressed using the Drosophila Schneider-2 (S2) cell expression system. Binding of conformationally sensitive antibodies as well as X-ray crystal structural studies indicate that the recombinant 80E subunits are properly folded native-like proteins. Combining the 80E subunits from each of the four dengue serotypes with ISCOMATRIX^® adjuvant, an adjuvant selected from a set of adjuvants tested for maximal and long lasting immune responses, results in high titer virus neutralizing antibody responses. Immunization of mice with a mixture of all four 80E subunits and ISCOMATRIX^® adjuvant resulted in potent virus neutralizing antibody responses to each of the four serotypes. The responses to the components of the tetravalent mixture were equivalent to the responses to each of the subunits administered individually. In an effort to evaluate the potential protective efficacy of the Drosophila expressed 80E, the dengue serotype 2 (DEN2-80E) subunit was tested in both the mouse and monkey challenge models. In both models protection against viral challenge was achieved with low doses of antigen in the vaccine formulation. In non-human primates, low doses of the tetravalent formulation induced good virus neutralizing antibody titers to all four serotypes and protection against challenge with the two dengue virus serotypes tested. In contrast to previous reports, where subunit vaccine candidates have generally failed to induce potent, protective responses, native-like soluble 80E proteins expressed in the Drosophila S2 cells and administered with appropriate adjuvants are highly immunogenic and capable of eliciting protective responses in both mice and monkeys. These results support the development of a dengue virus tetravalent vaccine based on the four 80E subunits produced in the Drosophila S2 cell expression system.     

Development of a small animal peripheral challenge model of Japanese encephalitis virus using interferon deficient AG129 mice and the SA14-14-2 vaccine virus strain

Japanese encephalitis virus (JEV) is the most common cause of viral encephalitis in Asia, and it is increasingly a global public health concern due to its recent geographic expansion. While commercial vaccines are available and used in some endemic countries, JEV continues to be a public health problem, with 50,000 cases reported annually. Research with virulent JEV in mouse models to develop new methods of prevention and treatment is restricted to BSL-3 containment facilities, confining these studies to investigators with access to these facilities. We have developed an adult small animal peripheral challenge model using interferon-deficient AG129 mice and the JEV live-attenuated vaccine SA14-14-2, thus requiring only BSL-2 containment. A low dose of virus (10 PFU/0.1 ml) induced 100% morbidity in infected mice. Increased body temperatures measured by implantable temperature transponders correlated with an increase in infectious virus and viral RNA in serum, spleen and brain as well as an increase in pro-inflammatory markers measured by a 58-biomarker multi-analyte profile (MAP) constructed during the course of infection. In the future, the MAP measurements can be used as a baseline for comparison in order to better assess the inhibition of disease progression by other prophylactic and therapeutic agents. The use of the AG129/JEV SA14-14-2 animal model makes vaccine and therapeutic studies feasible for laboratories with limited biocontainment facilities.     

A small animal peripheral challenge model of yellow fever using interferon-receptor deficient mice and the 17D-204 vaccine strain

Yellow fever virus (YFV), a member of the genus Flavivirus, is a mosquito-borne pathogen that requires wild-type (wt), virulent strains to be handled at biosafety level (BSL) 3, with HEPA-filtration of room air exhaust (BSL3+). YFV is found in tropical regions of Africa and South America and causes severe hepatic disease and death in humans. Despite the availability of effective vaccines (17D-204 or 17DD), YFV is still responsible for an estimated 200,000 cases of illness and 30,000 deaths annually. Besides vaccination, there are no other prophylactic or therapeutic strategies approved for use in human YF. Current small animal models of YF require either intra-cranial inoculation of YF vaccine to establish infection, or use of wt strains (e.g., Asibi) in order to achieve pathology. We have developed and characterized a BSL2, adult mouse peripheral challenge model for YFV infection in mice lacking receptors for interferons α, β, and γ (strain AG129). Intraperitoneal challenge of AG129 mice with 17D-204 is a uniformly lethal in a dose-dependent manner, and 17D-204-infected AG129 mice exhibit high viral titers in both brain and liver suggesting this infection is both neurotropic and viscerotropic. Furthermore the use of a mouse model permitted the construction of a 59-biomarker multi-analyte profile (MAP) using samples of brain, liver, and serum taken at multiple time points over the course of infection. This MAP serves as a baseline for evaluating novel therapeutics and their effect on disease progression. Changes (4-fold or greater) in serum and tissue levels of pro- and anti-inflammatory mediators as well as other factors associated with tissue damage were noted in AG129 mice infected with 17D-204 as compared to mock-infected control animals.     

Preclinical development of a dengue tetravalent recombinant subunit vaccine: Immunogenicity and protective efficacy in nonhuman primates

We describe here the preclinical development of a dengue vaccine composed of recombinant subunit carboxy-truncated envelope (E) proteins (DEN-80E) for each of the four dengue serotypes. Immunogenicity and protective efficacy studies in Rhesus monkeys were conducted to evaluate monovalent and tetravalent DEN-80E vaccines formulated with ISCOMATRIX™ adjuvant. Three different doses and two dosing regimens (0, 1, 2 months and 0, 1, 2, and 6 months) were evaluated in these studies. We first evaluated monomeric (DEN4-80E) and dimeric (DEN4-80EZip) versions of DEN4-80E, the latter generated in an attempt to improve immunogenicity. The two antigens, evaluated at 6, 20 and 100 μg/dose formulated with ISCOMATRIX™ adjuvant, were equally immunogenic. A group immunized with 20 μg DEN4-80E and Alhydrogel™ induced much weaker responses. When challenged with wild-type dengue type 4 virus, all animals in the 6 and 20 μg groups and all but one in the DEN4-80EZip 100 μg group were protected from viremia. Two out of three monkeys in the Alhydrogel™ group had breakthrough viremia. A similar study was conducted to evaluate tetravalent formulations at low (3, 3, 3, 6 μg of DEN1-80E, DEN2-80E, DEN3-80E and DEN4-80E respectively), medium (10, 10, 10, 20 μg) and high (50, 50, 50, 100 μg) doses. All doses were comparably immunogenic and induced high titer, balanced neutralizing antibodies against all four DENV. Upon challenge with the four wild-type DENV, all animals in the low and medium dose groups were protected against viremia while two animals in the high-dose group exhibited breakthrough viremia. Our studies also indicated that a 0, 1, 2 and 6 month vaccination schedule is superior to the 0, 1, and 2 month schedule in terms of durability. Overall, the subunit vaccine was demonstrated to induce strong neutralization titers resulting in protection against viremia following challenge even 8-12 months after the last vaccine dose.     

Scientific consultation on cell mediated immunity (CMI) in dengue and dengue vaccine development

Dengue is a re-emerging arboviral disease of great public health importance. Limited understanding of protective immune responses against dengue has hampered advancement of dengue vaccine candidates. Demonstrating an immunological correlate of protection has been limited to associating quantitative neutralizing antibody titers with clinical outcomes following infection. There have been a number of studies investigating the role of cell mediated immunity (CMI) in natural infections and these have demonstrated roles in both virus clearance and potentiating disease. Vaccine developers have extended the exploratory study of CMI in natural infection to the study of dengue vaccine recipients. Primary infections and monovalent vaccine administration generates dengue type-specific T-cell responses. Secondary infection, vaccination of flavivirus primed individuals, or administration of multivalent vaccine candidates results in broad, cross-reactive T-cell responses, similar to the broadening of antibody patterns. However, the precise function of CMI in protection or disease pathology remains ill-defined and, at present, there is no evidence to suggest that CMI can be utilized as a correlate of protection. Nonetheless, the study of CMI in natural infection and following vaccine administration should continue in an attempt to improve the understanding of dengue immunopathology, vaccine candidate immunogenicity, and potential correlates of protection.     

Detection of dengue cases by serological testing in a dengue vaccine efficacy trial: Utility for efficacy evaluation and impact of future vaccine introduction

BackgroundDengue diagnosis confirmation and surveillance are widely based on serological assays to detect anti-dengue IgM or IgG antibodies since such tests are affordable/user-friendly. The World Health Organization identified serological based diagnosis as a potential tool to define probable dengue cases in the context of vaccine trials, while acknowledging that this may have to be interpreted with caution.MethodsIn a phase IIb randomized, placebo-controlled trial assessing the efficacy of a tetravalent dengue vaccine (CYD-TDV) in Thai schoolchildren, case definition was based on virological confirmation by either serotype-specific RT-PCRs or by NS1-antigen ELISA (Clinicaltrials.gov NCT00842530). Here, we characterized suspected dengue cases using IgM and IgG ELISA to assess their utility in evaluating probable dengue cases in the context of vaccine efficacy trials, comparing virologically-confirmed and serologically diagnosed dengue in the vaccine and placebo groups. Serologically probable cases were defined as: (1) IgM positive acute- or convalescent-phase samples, or (2) IgG positive acute-phase sample and ≥4-fold IgG increase between acute and convalescent-phase samples.ResultsSerological diagnosis had good sensitivity (97.1%), but low specificity (85.1%) compared to virological confirmation. A high level of false positivity through serology diagnosis particularly in the 2 months post-vaccination was observed, and is most likely related to detection of the immune response to the dengue vaccine. This lack of specificity and bias with vaccination demonstrates the limitation of using IgM and IgG antibody responses to explore vaccine efficacy.ConclusionReliance on serological assessments would lead to a significant number of false positives during routine clinical practice and surveillance following the introduction of the dengue vaccine.     

Probing the attenuation and protective efficacy of a candidate chikungunya virus vaccine in mice with compromised interferon (IFN) signaling

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that causes explosive outbreaks of febrile illness associated with rash, and painful arthralgia. The CHIK vaccine strain 181/clone25 (181/25) developed by the United States Army Medical Research Institute of Infectious Diseases (USAMRIID) was shown to be well-tolerated and highly immunogenic in phase I and II clinical trials although it induced transient arthralgia in some healthy adult volunteers. In an attempt to better understand the host factors that are involved in the attenuating phenotype of CHIK 181/25 vaccine virus we conducted studies in interferon (IFN)-compromised mice and also evaluated its immunogenic potential and protective capacity. Infection of AG129 mice (defective in IFN-α/β and IFN-γ receptor signaling) with CHIK 181/25 resulted in rapid mortality within 3-4 days. In contrast, all infected A129 mice (defective in IFN-α/β receptor signaling) survived with temporary morbidity characterized by ruffled appearance and body weight loss. A129 heterozygote mice that retain partial IFN-α/β receptor signaling activity remained healthy. Infection of A129 mice with CHIK 181/25 induced significant levels of IFN-γ and IL-12 while the inflammatory cytokines, TNFα and IL-6 remained low. A single administration of the CHIK 181/25 vaccine provided both short-term and long-term protection (38 days and 247 days post-prime, respectively) against challenge with wt CHIKV-La Reunion (CHIKV-LR). This protection was at least partially mediated by antibodies since passively transferred immune serum protected both A129 and AG129 mice from wt CHIKV-LR and 181/25 virus challenge. Overall, these data highlight the importance of IFNs in controlling CHIK 181/25 vaccine and demonstrate the ability of this vaccine to elicit neutralizing antibody responses that confer short-and long-term protection against wt CHIKV-LR challenge.     

Immunogenicity and protective efficacy of the norovirus P particle-M2e chimeric vaccine in chickens

The ectodomain of the influenza matrix protein 2 (M2e) is highly conserved across strains and has been shown to be a promising candidate for universal influenza vaccine in the mouse model. In this study, we tested immune response and protective efficacy of a chimeric norovirus P particle containing the avian M2e protein against challenges with three avian influenza (AI) viruses (H5N2, H6N2, H7N2) in chickens. Two-week-old specific pathogen free chickens were vaccinated 3 times with an M2e-P particle (M2e-PP) vaccine via the subcutaneous (SQ) route with oil adjuvant, and transmucosal routes (intranasal, IN; eye drop, ED; microspray, MS) without adjuvant. M2e-PP vaccination via the SQ route induced significant IgG antibody responses which were increased by each booster vaccination. In groups vaccinated via IN, ED or MS, neither IgG nor IgA responses were detected from sera or nasal washes of immunized birds. The M2e-PP vaccination via the SQ route significantly reduced the virus shedding in the trachea and the cloaca for all three challenge viruses. Despite the absence of detectable IgG and IgA responses in birds vaccinated with the M2e-PP via intranasal routes, a similar level of reduction in virus shedding was observed in the IN group compared to the SQ group. Our results supports that the universal vaccine approach using M2e-based vaccine can provide cross-protection against challenge viruses among different HA subtypes although the efficacy of the vaccine should be enhanced further to be practical. Better understanding of the protective immune mechanism will be critical for the development of an M2e-based vaccine in chickens.     

A multi-country study of dengue vaccination strategies with Dengvaxia and a future vaccine candidate in three dengue-endemic countries: Vietnam,Thailand, and Colombia

BackgroundThe dengue vaccination era began when Dengvaxia (CYD-TDV) became available in 2016. In addition, several second-generation vaccine candidates are currently in phase 3 trials, suggesting that a broader availability of dengue vaccines may be possible in the near future. Advancing on the recent WHO-SAGE recommendations for the safe and effective use of CYD-TDV at the regional level on average, this study investigates the vaccination impacts and cost-effectiveness of CYD-TDV and of a hypothetical new vaccine candidate (NVC) in a country-specific manner for three endemic countries: Vietnam, Thailand, and Colombia.MethodsThe vaccination impacts of CYD-TDV and NVC were derived by fitting the empirical seroprevalence rates of 9 year olds into an individual-based meta-population transmission model, previously used for the WHO-SAGE working group. The disability-adjusted life years were estimated by applying country-specific parametric values. The cost-effectiveness analyses of four intervention strategies in combination with routine and catch-up campaigns were compared for both vaccines to inform decision makers regarding the most suitable immunization program in each of the three countries.Results and conclusionBoth CYD-TDV and NVC could be cost-effective at the DALY threshold cost of $2000 depending upon vaccination costs. With CYD-TDV, targeting 9 year olds in routine vaccination programs and 10–29 year olds as a one-off catch-up campaign was the most cost-effective strategy in all three countries. With NVC, while the most cost-effective strategy was to vaccinate 9–29 and 9–18 year olds in Vietnam and Thailand respectively, vaccinating younger age cohorts between 1 and 5 years old in Colombia was more cost-effective than other strategies. Given that three countries will soon face decisions regarding whether and how to incorporate CYD-TDV or future dengue vaccines into their budget-constrained national immunization programs, the current study outcomes can be used to help decision makers understand the expected impacts and cost-effectiveness of such vaccines.     

A novel dengue virus serotype-2 nanovaccine induces robust humoral and cell-mediated immunity in mice

Dengue virus (DENV), a member of the Flaviviridae family, can be transmitted to humans through the bite of infected Aedes mosquitoes. The incidence of dengue has increased worldwide over the past few decades. Inadequate vector control, changing global ecology, increased urbanization, and faster global travel are factors enhancing the rapid spread of the virus and its vector. In the absence of specific antiviral treatments, the search for a safe and effective vaccine grows more imperative. Many strategies have been utilized to develop dengue vaccines. Here, we demonstrate the immunogenic properties of a novel dengue nanovaccine (DNV), composed of ultraviolet radiation (UV)-inactivated DENV-2, which has been loaded into the nanoparticles containing chitosan/Mycobacterium bovis Bacillus Calmette-Guerin cell wall components (CS/BCG-NPs). We investigated the immunogenicity of DNV in a Swiss albino mouse model. Inoculation with various concentrations of vaccine (0.3, 1, 3 and 10 μg/dose) with three doses, 15-day apart, induced strong anti-dengue IgM and IgG antibodies in the mouse serum along with neutralizing antibody against DENV-2 reference strain (16681), a clinical-isolate strain (00745/10) and the mouse-adapted New Guinea-C (NGC) strain. Cytokine and chemokine secretion in the serum of DNV-immunized mice showed elevated levels of IFN-γ, IL-2, IL-5, IL-12p40, IL-12p70, IL-17, eotaxin and RANTES, all of which have varying immune functions. Furthermore, we observed a DNV dose-dependent increase in the frequencies of IFN-γ-producing CD4⁺ and CD8⁺ T cells after in vitro stimulation of nucleated cells. Based on these findings, DNV has the potential to become a candidate dengue vaccine.     

A tetravalent recombinant dengue domain III protein vaccine stimulates neutralizing and enhancing antibodies in mice

Dengue viruses co-circulate as four serologically distinct viruses (DENV1-4) that commonly infect individuals sequentially. Current DENV candidate vaccines incorporate the entire virion envelope E protein (E) ectodomain thereby stimulating both DENV serotype-specific and cross-reactive antibodies. Because the latter may enhance naturally acquired infection, such vaccine formulations must be tetravalent. We evaluated the neutralizing and enhancing antibody response to E domain III (dIII) proteins, in which serotype-specific neutralizing determinants are concentrated. Mice immunized with insect cell-secreted recombinant DENV-dIII proteins individually, and in tetravalent combination, produced serotype-specific IgG1 neutralizing antibodies that nevertheless exhibited measurable DENV enhancing activity in FcγR-bearing cells. Vaccine strategies directed to DENV-dIII-targeted neutralizing antibody production remain attractive but will likely require further modifications to induce safe, protective immunity.     

Enhanced immunogenicity and protective efficacy of a tetravalent dengue DNA vaccine using electroporation and intradermal delivery

Phase 1 clinical trials with a DNA vaccine for dengue demonstrated that the vaccine is safe and well tolerated, however it produced less than optimal humoral immune responses. To determine if the immunogenicity of the tetravalent dengue DNA vaccine could be enhanced, we explored alternate, yet to be tested, methods of vaccine administration in non-human primates. Animals were vaccinated on days 0, 28 and 91 with either a low (1 mg) or high (5 mg) dose of vaccine by the intradermal or intramuscular route, using either needle-free injection or electroporation devices. Neutralizing antibody, IFN-γ T cell and memory B cell responses were compared to a high dose group vaccinated with a needle-free intramuscular injection delivery device similar to what had been used in previous preclinical and clinical studies. All previously untested vaccination methodologies elicited improved immune responses compared to the high dose needle-free intramuscular injection delivery group. The highest neutralizing antibody responses were observed in the group that was vaccinated with the high dose formulation via intradermal electroporation. The highest IFN-γ T cell responses were also observed in the high dose intradermal electroporation group and the CD8⁺ T cells were the dominant contributors for the IFNγ response. Memory B cells were detected for all four serotypes. More than a year after vaccination, groups were challenged with dengue-1 virus. Both the low and high dose intradermal electroporation groups had significantly fewer days of dengue-1 virus RNAemia compared to the control group. The results from this study demonstrate that using either an electroporation device and/or the intradermal route of delivery increases the immune response generated by this vaccine in non-human primates and should be explored in humans.     

Immunogenicity of an adenoviral-based Middle East Respiratory Syndrome coronavirus vaccine in BALB/c mice

A new type of coronavirus has been identified as the causative agent underlying Middle East Respiratory Syndrome (MERS). The MERS coronavirus (MERS-CoV) has spread in the Middle East, but cases originating in the Middle East have also occurred in the European Union and the USA. Eight hundred and thirty-seven cases of MERS-CoV infection have been confirmed to date, including 291 deaths. MERS-CoV has infected dromedary camel populations in the Middle East at high rates, representing an immediate source of human infection. The MERS-CoV spike (S) protein, a characteristic structural component of the viral envelope, is considered as a key target of vaccines against coronavirus infection. In an initial attempt to develop a MERS-CoV vaccine to ultimately target dromedary camels, we constructed two recombinant adenoviral vectors encoding the full-length MERS-CoV S protein (Ad5.MERS-S) and the S1 extracellular domain of S protein (Ad5.MERS-S1). BALB/c mice were immunized with both candidate vaccines intramuscularly and boosted three weeks later intranasally. All the vaccinated animals had antibody responses against spike protein, which neutralized MERS-CoV in vitro. These results show that an adenoviral-based vaccine can induce MERS-CoV-specific immune responses in mice and hold promise for the development of a preventive vaccine that targets the animal reservoir, which might be an effective measure to eliminate transmission of MERS-CoV to humans.     

Estimation of parameters related to vaccine efficacy and dengue transmission from two large phase III studies

BackgroundA tetravalent dengue vaccine was shown to be efficacious against symptomatic dengue in two phase III efficacy studies performed in five Asian and five Latin American countries. The objective here was to estimate key parameters of a dengue transmission model using the data collected during these studies.MethodsParameter estimation was based on a Sequential Monte Carlo approach and used a cohort version of the transmission model. Serotype-specific basic reproduction numbers were derived for each country. Parameters related to serotype interactions included duration of cross-protection and level of cross-enhancement characterized by differences in symptomaticity for primary, secondary and post-secondary infections. We tested several vaccine efficacy profiles and simulated the evolution of vaccine efficacy over time for the scenarios providing the best fit to the data.ResultsTwo reference scenarios were identified. The first included temporary cross-protection and the second combined cross-protection and cross-enhancement upon wild-type infection and following vaccination. Both scenarios were associated with differences in efficacy by serotype, higher efficacy for pre-exposed subjects and against severe dengue, increase in efficacy with doses for naïve subjects and by a more important waning of vaccine protection for subjects when naïve than when pre-exposed. Over 20 years, the median reduction of dengue risk induced by the direct protection conferred by the vaccine ranged from 24% to 47% according to country for the first scenario and from 34% to 54% for the second.ConclusionOur study is an important first step in deriving a general framework that combines disease dynamics and mechanisms of vaccine protection that could be used to assess the impact of vaccination at a population level.     

Immunogenicity and safety of a tetravalent dengue vaccine and a bivalent HPV vaccine given concomitantly or sequentially in girls aged 9 to 14 years in Mexico

Dengue is endemic in several regions, and the global incidence is increasing. The recombinant, live, attenuated, tetravalent dengue vaccine (CYD-TDV) is recommended for dengue seropositive individuals ≥ 9 years. Human papillomavirus (HPV) vaccination is recommended for girls aged 9–14 years to prevent HPV infection-related cancers. This study assessed the immunogenicity and safety of a bivalent HPV (types 16 and 18) vaccine and CYD-TDV when co-administered concomitantly or sequentially.This was a Phase IIIb, randomized, open-label, multicenter study in girls aged 9–14 years in Mexico (NCT02979535). Participants were randomized 1:1 to receive three doses of CYD-TDV 6 months apart and two doses of bivalent HPV vaccine either concomitantly with, or 1 month before (sequentially), the first 2 CYD-TDV doses. Antibody levels were measured at baseline and 28-days after each vaccine dose for all participants, using an enzyme-linked immunosorbent assay for HPV-16 and HPV-18 antibodies, and a plaque reduction neutralization test for the four dengue serotypes; results are reported only for participants who were seropositive at baseline. Safety was assessed for all randomized participants throughout the study.Of the randomized participants, 305/478 (63.8%) were seropositive for dengue at baseline: 154 in the concomitant group and 151 in the sequential group. After the last HPV vaccine dose, the antibody titers for HPV were comparable in seropositive participants between treatment groups, with between group titer ratios of 0.966 for HPV-16 and 0.999 for HPV-18. After dose 3 of CYD-TDV, antibody titers were comparable for the concomitant and sequential groups across all serotypes, with between-group ratios close to 1 (serotype 1: 0.977; serotype 2: 0.911; serotype 3: 0.921; serotype 4: 0.931).CYD-TDV and a bivalent HPV vaccine administered concomitantly or sequentially in dengue seropositive girls aged 9–14 years elicited comparable immune responses with similar safety profiles.     

Immunogenicity and efficacy of orally administered inactivated influenza virus vaccine in mice

The immunogenicity and protective efficacy of formalin-inactivated whole influenza A/Bangkok/79 virus vaccine given to unprimed Swiss mice orally in capsules, in their drinking water, or by direct injection into the duodenum were studied. Virus-specific IgG and IgA antibody responses to all these methods were dose-dependent and varied according to immunization conditions. Following intranasal challenge with live A/Bangkok influenza virus, mice given greater than or equal to 66 micrograms haemagglutinin (HA) of vaccine in drinking water or capsules, and mice injected into the duodenum with greater than or equal to 0.66 microgram HA, had significantly lower virus titres in their noses and lungs than control mice comparably inoculated.