Immunogenicity of a killed bivalent whole cell oral cholera vaccine in forcibly displaced Myanmar nationals in Cox's Bazar, Bangladesh

After the large influx of Rohingya nationals (termed Forcibly Displaced Myanmar National; FDMN) from Rakhine State of Myanmar to Cox’s Bazar in Bangladesh, it was apparent that outbreaks of cholera was very likely in this setting where people were living under adverse water and sanitation conditions. Large campaigns of oral cholera vaccine (OCV) were carried out as a preemptive measure to control cholera epidemics. The aim of the study was to evaluate the immune responses of healthy adults and children after administration of two doses of OCV at 14 days interval in FDMN population and compare with the response observed in Bangladeshi’s vaccinated earlier. A cross-sectional immunogenicity study was conducted among FDMNs of three age cohort; in adults (18+years; n = 83), in older children (6–17 years; n = 63) and in younger children (1–5 years; n = 80). Capillary blood was collected at three time points to measure vibriocidal antibodies using either plasma or dried blood spot (DBS) specimens. There was a significant increase of responder frequency of vibriocidal antibody titer at day 14 in all groups for Vibrio cholerae O1 (Ogawa/Inaba: adults-64%/64%, older children-70%/89% and younger children-51%/75%). There was no overall difference of vibriocidal antibody titer between FDMN and Bangladeshi population at baseline (p = 0.07–0.08) and at day 14, day 28 in all age groups for both serotypes. The seroconversion rate and geometric mean titer (GMT) of either serotype were comparable using both plasma and DBS specimens. These results showed that OCV is capable of inducing robust immune responses in adults and children among the FDMN population which is comparable to that seen in Bangladeshi participants in different age groups or that reported from other cholera endemic countries. Our results also suggest that the displaced population were exposed to V. cholerae prior to seeking shelter in Bangladesh.在大量缅甸若开邦罗兴亚民众（被称为被迫流离失所的缅甸国民，Forcibly Displaced Myanmar National，以下简称FDMN）涌入孟加拉国科克斯巴扎尔地区后，由于当地民众居住环境的饮水与卫生条件恶劣，霍乱暴发风险极高。当地遂开展大规模口服霍乱疫苗（oral cholera vaccine，以下简称OCV）接种，作为防控霍乱流行的预防性措施。本研究旨在评估FDMN人群间隔14天接种两剂OCV后，健康成人与儿童的免疫应答水平，并与此前孟加拉国接种人群的应答情况进行对比。本研究针对三个年龄队列的FDMN人群开展了横断面免疫原性研究：成人组（18岁及以上，n=83）、大龄儿童组（6~17岁，n=63）与低龄儿童组（1~5岁，n=80）。在三个时间点采集毛细血管血样本，分别采用血浆或干血斑（dried blood spot，以下简称DBS）标本检测杀弧菌抗体滴度。针对O1群霍乱弧菌（Vibrio cholerae O1）的小川型（Ogawa）与稻叶型（Inaba），所有组别在接种后第14天的杀弧菌抗体滴度应答率均显著提升：成人组分别为64%/64%，大龄儿童组为70%/89%，低龄儿童组为51%/75%。在基线时、接种后第14天与第28天，所有年龄组的两种血清型杀弧菌抗体滴度，在FDMN人群与孟加拉国人群间均无统计学差异（p=0.07~0.08）。采用血浆与DBS标本检测得到的两种血清型的血清转换率与几何平均滴度（geometric mean titer，以下简称GMT）均无显著差异。本研究结果显示，OCV可在FDMN人群的成人与儿童中诱导强烈的免疫应答，该应答水平与不同年龄组的孟加拉国接种人群，以及其他霍乱流行区已报道的研究结果相当。此外，本研究结果提示，该流离失所人群在抵达孟加拉国寻求庇护前，已接触过O1群霍乱弧菌。