Challenges in prevaccination screening for previous dengue infection (2020)

Dengue is an acute mosquito-borne viral disease that affects approximately 100 million people per year worldwide.1Bhatt S Gething PW Brady OJ et al.The global distribution and burden of dengue.Nature. 2013; 496: 504-507Crossref PubMed Scopus (4837) Google Scholar The arrival of licensed vaccines against dengue virus is thus much welcomed to reduce this global disease burden. Dengvaxia (Sanofi Pasteur), a chimeric yellow fever–dengue tetravalent dengue vaccine, has been licensed for use in several countries. However, this vaccine is indicated only in those with previous dengue virus infection; vaccination in those without previous dengue infection is associated with increased risk of severe dengue if wild-type dengue virus infection occurs.2Sridhar S Luedtke A Langevin E et al.Effect of dengue serostatus on dengue vaccine safety and efficacy.N Engl J Med. 2018; 379: 327-340Crossref PubMed Scopus (306) Google Scholar A second dengue vaccine, TAK003 (Takeda Vaccines), has completed phase 3 trials,3Biswal S Reynales H Saez-Llorens X et al.Efficacy of a tetravalent dengue vaccine in healthy children and adolescents.N Engl J Med. 2019; 381: 2009-2019Crossref PubMed Scopus (80) Google Scholar and is expected to be licensed soon. Although no increased risk of severe dengue in those receiving this vaccine without previous dengue virus infection has been observed thus far, the efficacy of this vaccine is nonetheless higher and more durable in those with previous infection.4Biswal S Borja-Tabora C Martinez Vargas L et al.Efficacy of a tetravalent dengue vaccine in healthy children aged 4–16 years: a randomised, placebo-controlled, phase 3 trial.Lancet. 2020; 395: 1423-1433Summary Full Text Full Text PDF PubMed Scopus (28) Google Scholar Prevaccination screening for previous dengue virus infection is thus required for the use of Dengvaxia and could, in some instances, even become an important aspect of future dengue vaccination programmes. In this issue of The Lancet Global Health, Anna Lena Lopez and colleagues5Lopez AL Adams C Ylade M et al.Determining dengue virus serostatus by indirect IgG ELISA compared with focus reduction neutralisation test in children in Cebu, Philippines: a prospective population-based study.Lancet Glob Health. 2021; 9: e44-e51Summary Full Text Full Text PDF PubMed Scopus (6) Google Scholar evaluated the performance of a commercially available dengue IgG indirect ELISA in determining dengue serostatus as a prevaccination screening tool, using sera prospectively collected from 2996 children. This ELISA, which uses the viral envelope protein as the capture antigen, has been previously evaluated as a prevaccination screening tool. However, these previous studies have used the cutoff values for seropositivity as stated in the product insert. Because the ELISA was not primarily developed for prevaccination screening, the authors first sought to identify a revised ELISA index to define seropositivity for previous dengue virus infection in a dengue-endemic population. The authors compared the ELISA results from 65·5% of the serum samples with those obtained from a focus reduction neutralisation test (FRNT), a gold standard in dengue serology, to identify those with previous dengue virus infection in a prospectively enrolled cohort of children who were to be aged 9–14 years at the time of a mass dengue vaccination campaign. Reactivity on FRNT was also used to define whether the previous dengue infections were of one (monotypic) or more (multitypic) dengue virus serotypes. A receiver operating characteristics curve was then constructed to define the ELISA index value cutoff for seropositivity for previous dengue infection. It is noteworthy that the cutoff value determined in this study (0·9) was the same as the lower limit of the indeterminate range (0·9–1·1) indicated in the product insert. Using this newly defined cutoff, the authors found that, for identifying previous dengue infection, the ELISA had a sensitivity of 95·2% and a specificity of 93·4%. However, when applied to those with monotypic dengue virus infection only (not multitypic), the sensitivity decreased to 77·1%, although the specificity remained at 93·4%.5Lopez AL Adams C Ylade M et al.Determining dengue virus serostatus by indirect IgG ELISA compared with focus reduction neutralisation test in children in Cebu, Philippines: a prospective population-based study.Lancet Glob Health. 2021; 9: e44-e51Summary Full Text Full Text PDF PubMed Scopus (6) Google Scholar These findings raise several issues. The 93·4% specificity of the ELISA found in this assay might be insufficient to prevent a sizeable proportion of individuals from testing false positive and thus being wrongly vaccinated and placed at elevated risk of severe dengue upon wild-type dengue virus exposure.6Hunsperger E Peeling R Gubler DJ Ooi EE Dengue pre-vaccination serology screening for the use of Dengvaxia.J Travel Med. 2019; 26taz092Crossref PubMed Scopus (13) Google Scholar For the specificity determined in this study, both the point estimate and the 95% CI are lower than those previously reported.6Hunsperger E Peeling R Gubler DJ Ooi EE Dengue pre-vaccination serology screening for the use of Dengvaxia.J Travel Med. 2019; 26taz092Crossref PubMed Scopus (13) Google Scholar An obvious explanation is the revised cutoff value for seropositivity. The lowered cutoff ELISA index value could have increased sensitivity at the expense of specificity. Restoring the more stringent ELISA index value for seropositivity could arguably be prudent. However, this argument raises an ethical issue: the sensitivity of the proposed modified ELISA index, as shown in this study, is already significantly lower in those with monotypic previous dengue virus infection compared with multitypic infection.5Lopez AL Adams C Ylade M et al.Determining dengue virus serostatus by indirect IgG ELISA compared with focus reduction neutralisation test in children in Cebu, Philippines: a prospective population-based study.Lancet Glob Health. 2021; 9: e44-e51Summary Full Text Full Text PDF PubMed Scopus (6) Google Scholar Reducing sensitivity further would deprive a sizeable proportion of those with monotypic infection from benefiting from vaccination for reduced risk of severe dengue. A better performing prevaccination screening test is thus clearly an urgent need. Unlike in previous studies,7Bonaparte M Zheng L Garg S et al.Evaluation of rapid diagnostic tests and conventional enzyme-linked immunosorbent assays to determine prior dengue infection.J Travel Med. 2019; 26taz078Crossref PubMed Scopus (22) Google Scholar, 8Bonaparte M Huleatt J Hodge S et al.Evaluation of dengue serological tests available in Puerto Rico for identification of prior dengue infection for prevaccination screening.Diagn Microbiol Infect Dis. 2020; 96114918Crossref PubMed Scopus (8) Google Scholar Lopez and colleagues took a longitudinal approach to serum sampling in a dengue endemic population. The findings reported here thus represent a real-world performance of the ELISA as a prevaccination screening test. However, there are subtle but important issues in this study. First, although FRNT is the gold-standard test to differentiate dengue virus from other flaviviral infections, it might not have high enough sensitivity to detect low levels of dengue antibodies. The use of FRNT positivity alone could therefore underestimate the true rate of previous dengue infection. Second, variations in assay conditions, including the strains of dengue virus used, could impact FRNT titre results and make comparisons with findings from other studies challenging.9Thomas SJ Nisalak A Anderson KB et al.Dengue plaque reduction neutralization test (PRNT) in primary and secondary dengue virus infections: how alterations in assay conditions impact performance.Am J Trop Med Hyg. 2009; 81: 825-833Crossref PubMed Scopus (135) Google Scholar Standardising the assay conditions, as well as the minimum titres that define both monotypic and multitypic previous dengue infection, remains an urgent need. Results from this and other studies should spur urgent dengue serology standardisation, especially of the gold-standard virus neutralisation test,10Roehrig JT Hombach J Barrett AD Guidelines for plaque-reduction neutralization testing of human antibodies to dengue viruses.Viral Immunol. 2008; 21: 123-132Crossref PubMed Scopus (226) Google Scholar to support implementation of dengue vaccination. EEO reports personal fees from Sanofi Pasteur and Takeda Vaccines, with relevance to the current work; and grants from National Medical Research Council, Singapore, and is a member of the scientific advisory board on vaccines for Arcturus Therapeutics, outside the submitted work. Determining dengue virus serostatus by indirect IgG ELISA compared with focus reduction neutralisation test in children in Cebu, Philippines: a prospective population-based studyMost children (89·3%) assessed in our study and eligible to participate in the mass dengue vaccination campaign were seropositive for previous dengue virus infection. Compared with FRNT, ELISA had high sensitivity and specificity (>90%), but the false-negative and false-positive rates makes the test suboptimal for prevaccination screening. Individuals who are falsely identified as seropositive by dengue IgG ELISA and then vaccinated might be at risk of developing severe disease during a subsequent exposure to wild-type dengue virus. Full-Text PDF Open Access