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Background During August 2017–January 2018, more than 700,000 forcibly displaced Rohingyas crossed into Cox’s Bazar, Bangladesh. In response to measles and diphtheria cases, first documented in September and November 2017, respectively, vaccination campaigns targeting children 6 years were not assessed. In MSs, measles seroprotection was similarly high among 1- to 6-year-olds and 7- to 14-year-olds (91% [95% CI 86%–94%] and 99% [95% CI 96%–100%], respectively, p < 0.001). Rubella and diphtheria seroprotection in MSs were significantly lower among 1- to 6-year-olds (84% [95% CI 79%–88%] and 63% [95% CI 56%–70%]) compared to 7- to 14-year-olds (96% [95% CI 90%–98%] and 77% [95% CI 69%–84%]) (p < 0.001). Tetanus seroprevalence was similar among 1- to 6-year-olds and 7- to 14-year-olds (76% [95% CI 69%–81%] and 84% [95% CI 77%–89%], respectively; p = 0.07). Vaccination campaign coverage was consistent with seroprotection in both camps. However, nonresponse, the main limitation of the study, may have biased the seroprotection and campaign coverage results. Conclusions In this study, we observed that despite multiple vaccination campaigns, immunity gaps exist among children in MSs, particularly for diphtheria, which requires serial vaccinations to achieve maximum protection. Therefore, an additional tetanus-diphtheria campaign may be warranted in MSs to address these remaining immunity gaps. Rapid scale-up and strengthening of routine immunization services to reach children and to deliver missed doses to older children is also critically needed to close immunity gaps and prevent future outbreaks., In a cross-sectional study, Leora R. Feldstein and colleagues investigate vaccination coverage and seroprevalence among forcibly-displaced Rohingya children in Cox’s Bazar, Bangladesh in 2018., Author summary Why was this study done? Rohingyas living in camps and makeshift settlements (MSs) are at risk of outbreaks of vaccine-preventable diseases (VPDs). Ongoing outbreaks of measles and diphtheria, despite vaccination campaigns, suggest gaps in immunity for some children. We conducted this survey among Rohingya children to better understand these immunity gaps and risk for ongoing and future outbreaks of VPDs. What did the researchers do and find? We conducted a cross-sectional serologic and vaccine coverage survey in 2 camps in April and May 2018. The youngest children living in the MSs, who are more recent arrivals from Myanmar, had low levels of seroprotection for rubella (84% of children), diphtheria (63%), and tetanus (76%). Seroprotection for the youngest children living in Nayapara registered camp was high for measles, rubella, diphtheria, and tetanus (91%–98% of children). What do these findings mean? These findings suggest that despite vaccination campaigns, immunity gaps remain for VPDs, especially among children who are more recent arrivals from Myanmar and now live in MSs. Remaining immunity gaps may increase the risk of outbreaks of VPDs. An additional diphtheria-tetanus containing vaccine (DTCV) campaign may be beneficial to address the very low seroprotection levels identified among children living in the MSs. Rapid scale-up of routine immunization services is necessary to close remaining immunity gaps among children and those that have missed campaign opportunities. Nonresponse, the main limitation of this study, may have biased the seroprotection and campaign coverage results.

Background We performed a cross-sectional survey in April–May 2018 among Rohingya in Cox’s Bazar, Bangladesh, to assess polio immunity and inform vaccination strategies. Methods and findings Rohingya children aged 1–6 years (younger group) and 7–14 years (older group) were selected using multi-stage cluster sampling in makeshift settlements and simple random sampling in Nayapara registered camp. Surveyors asked parents/caregivers if the child received any oral poliovirus vaccine (OPV) in Myanmar and, for younger children, if the child received vaccine in any of the 5 campaigns delivering bivalent OPV (serotypes 1 and 3) conducted during September 2017–April 2018 in Cox’s Bazar. Dried blood spot (DBS) specimens were tested for neutralizing antibodies to poliovirus types 1, 2, and 3 in 580 younger and 297 older children. Titers ≥ 1:8 were considered protective. Among 632 children (335 aged 1–6 years, 297 aged 7–14 years) enrolled in the study in makeshift settlements, 51% were male and 89% had arrived after August 9, 2017. Among 245 children (all aged 1–6 years) enrolled in the study in Nayapara, 54% were male and 10% had arrived after August 9, 2017. Among younger children, 74% in makeshift settlements and 92% in Nayapara received >3 bivalent OPV doses in campaigns. Type 1 seroprevalence was 85% (95% CI 80%–89%) among younger children and 91% (95% CI 86%–95%) among older children in makeshift settlements, and 92% (88%–95%) among younger children in Nayapara. Type 2 seroprevalence was lower among younger children than older children in makeshift settlements (74% [95% CI 68%–79%] versus 97% [95% CI 94%–99%], p < 0.001), and was 69% (95% CI 63%–74%) among younger children in Nayapara. Type 3 seroprevalence was below 75% for both age groups and areas. The limitations of this study are unknown routine immunization history and poor retention of vaccination cards. Conclusions Younger Rohingya children had immunity gaps to all 3 polio serotypes and should be targeted by future campaigns and catch-up routine immunization. DBS collection can enhance the reliability of assessments of outbreak risk and vaccination strategy impact in emergency settings., Concepción Fernandez Estívariz et al report that Rohingya children aged 1-6 years have immunity gaps to all polio serotypes and should be targeted by future campaigns for catch up immunisation., Author summary Why was this study done? Between August 2017 and January 2018, almost 700,000 Rohingya people arrived in Cox’s Bazar District, Bangladesh, and settled in 2 refugee camps and in makeshift settlements around the camps. Crowding and inadequate access to safe water, sanitation, and healthcare facilitated outbreaks of infectious diseases that spread to the surrounding community. Ongoing outbreaks of measles and diphtheria in May 2018, despite several vaccination campaigns, suggested that some children remained unprotected for vaccine-preventable diseases. We conducted this survey to evaluate immunity against poliovirus and guide new vaccination activities. What did the researchers do and find? We conducted a cross-sectional survey among Rohingya children 1–14 years of age during April–May 2018 that included an interview about vaccines received in recent campaigns and collection of blood samples through finger prick to test for antibodies against poliovirus. Protection against poliovirus type 1 was lower among children aged below 7 years than in older children in the makeshift settlements, despite most children having received several doses of oral polio vaccine in campaigns. Protection against all poliovirus was lowest in children below 3 years of age. What do these findings mean? These findings suggested that children below 7 years of age recently arrived in the camp/settlements had immunity gaps after the vaccination campaigns that increased the risk of polio outbreaks. Based upon this information, we recommended to the agencies that conducted the campaigns that they include polio vaccines in future campaigns targeting only children below 5 years of age. Rapid scale-up of routine immunization services would be necessary to close immunity gaps among children below 2 years of age. Collection of dried blood specimens through finger prick for antibody testing is feasible in emergency settings, and provides crucial information for assessment of outbreak risk and impact of outbreak response strategies.