Seroepidemiology and Carriage of Diphtheria in Epidemic-Prone Area and Implications for Vaccination Policy, Vietnam

Abstract

D iphtheria is an infectious disease caused by toxigenic strains of Corynebacterium diphtheriae, C. ulcerans, and, rarely, C. pseudotuberculosis (1-3). Although the diphtheria toxoid vaccine contributed to a decrease in the number of diphtheria cases globally, the disease remains a threat to public health, particularly in South and Southeast Asia (4,5).Currently, the World Health Organization recommends 3 primary doses of the diphtheria-tetanuspertussis (DTP) vaccine in young infants (i.e., at 6, 10, and 14 weeks of age), followed by 3 booster doses at 12-23 months, 4-7 years, and 9-15 years of age, to protect all age groups. Nevertheless, many low-and middle-income countries have not introduced all booster doses.The Vietnamese Ministry of Health (MOH) first introduced DTP in 1981, targeting infants 2, 3, and 4 months of age. A booster dose targeting children 18 months of age was introduced during 2011 (6). Because of efforts in vaccination, reported diphtheria cases in Vietnam decreased to nearly zero by 2010. However, several small diphtheria outbreaks in remote districts in central and western Vietnam have been observed since 2013 (7).Supplemental immunization activities (SIAs), in which vaccination is delivered to all targeted persons regardless of their previous vaccination history, were conducted in the areas surrounding Quang Ngai Province when diphtheria cases were identified during 2013-2019 (8). However, most of the population of Quang Ngai Province has not been covered by SIAs as of October 2019. According to the national surveillance program, Quang Ngai Province reported 2 laboratory-confirmed cases in 2017-2018 and 47 in 2019-2020, among an estimated population of 1,231,697 (9). Among these cases, 36 (73%) cases were in school-age children (6-17 years of age). Among confirmed cases, 3 (6%) were fatal.Although national administrative coverage of 3 doses of DTP among infants has been maintained

Sero and Carriage Epidemiology of Pertussis in Urban and Rural Regions in Vietnam

“…This study observed a lower proportion of participants with a confirmed history of DPT vaccination in Quang Ngai than that in Nha Trang. In addition, our previous study detected a lower seroprevalence of anti-diphtheria toxoid IgG among children aged 1–5 years in Quang Ngai (36%) than in Nha Trang (68%) [ 12 ]. A similar pattern was observed with a lower prevalence of an anti-PT IgG of ≥62.5 IU/mL (29%) among the ages 0–2 years in Quang Ngai compared with that in Nha Trang (48%) in this study.…”

“…It is an area with limited health access due to its mountainous topography, where three diphtheria cases were reported between January and September 2019. A total of 1500 participants were approached for enrollment as follows: 350, 400, 400, and 350 for age groups 1–5, 6–17, 18–40, and 41–55 years, respectively, based on the previously measured diphtheria seroprevalence in Vietnam using multi-stage cluster sampling [ 12 ]. This survey was originally conducted for diphtheria serosurveillance.…”

“…Serum samples from the surveys in Nha Trang and dried blood samples (DBS) on the Whatman 903 protein saver card (Cytiva, Marlborough, USA) from the survey in Quang Ngai were stored at −80 °C at the Pasteur Institute in Nha Trang. DBS was punched out with a 6 mm hole punch, eluted with 500 μL elution buffer (phosphate-buffered saline), and incubated overnight at 4 °C [ 12 ]. The supernatant of the eluted solution of DBS and thawed serum samples were used to measure the level of anti-PT IgG using a commercially available enzyme-linked immunosorbent assay (ELISA) kit (Abcam, Cambridge, UK) following the manufacturer’s protocol.…”

“…This study aimed to estimate the prevalence of recent pertussis infection serologically in a subset of not recently vaccinated children and adults by age groups and its associated factors in a community in Nha Trang, a city, and in Quang Ngai, a remote area in Vietnam. The Quang Ngai survey was additionally conducted, as this area experienced three diphtheria cases in 2019 [ 12 ]. Our previous study on diphtheria seroprevalence targeted the same samples as this study, which estimated that the DPT coverage was lower in Quang Ngai than in Nha Trang, as the diphtheria seroprevalence among persons aged 1–5 years was lower in Quang Ngai than in Nha Trang, in addition to the incidence of diphtheria cases.…”

“…Our previous study on diphtheria seroprevalence targeted the same samples as this study, which estimated that the DPT coverage was lower in Quang Ngai than in Nha Trang, as the diphtheria seroprevalence among persons aged 1–5 years was lower in Quang Ngai than in Nha Trang, in addition to the incidence of diphtheria cases. Therefore, we regarded Nha Trang as a high-vaccine-coverage area and Quang Ngai as a low-coverage area [ 12 ]. We also investigated waning and acquiring antibodies for the pertussis toxin over a two-year follow-up period and the factors associated with this change.…”