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BackgroundAlthough high vaccine effectiveness of messenger RNA (mRNA) coronavirus disease 2019 (COVID-19) vaccines was reported in studies in several countries, data is limited from Asian countries, especially against the Delta (B.1.617.2) variant. MethodsWe conducted a multicenter test-negative case-control study in patients aged [≥]16 visiting hospitals or clinics with signs or symptoms consistent with COVID-19 from July 1 to September 30, 2021, when the Delta variant was dominant ([≥]90% of severe acute respiratory syndrome coronavirus 2 [SARS-CoV-2] infections) nationwide in Japan. Vaccine effectiveness of BNT162b2 or mRNA-1273 against symptomatic SARS-CoV-2 infections was evaluated. Waning immunity among patients aged 16 to 64 was also assessed. ResultsWe enrolled 1936 patients, including 396 test-positive cases and 1540 test-negative controls for SARS-CoV-2. The median age was 49 years, 53.4% were male, and 34.0% had underlying medical conditions. Full vaccination (receiving two doses [≥]14 days before symptom onset) was received by 6.6% of cases and 38.8% of controls. Vaccine effectiveness of full vaccination against symptomatic SARS-CoV-2 infections was 88.7% (95% confidence interval [CI], 78.8-93.9) among patients aged 16 to 64 and 90.3% (95% CI, 73.6-96.4) among patients aged [≥]65. Among patients aged 16 to 64, vaccine effectiveness within one to three months after full vaccination was 91.8% (95% CI, 80.3-96.6), and was 86.4% (95% CI, 56.9-95.7) within four to six months. ConclusionsmRNA COVID-19 vaccines had high effectiveness against symptomatic SARS-CoV-2 infections in Japan during July 1 to September 30, 2021, when the Delta variant was dominant nationwide.
ABSTRACT
BackgroundAfter the first case of COVID-19 in Japan on 15 January 2020, multiple nationwide COVID-19 clusters were identified by the end of February. The Japanese government focused on mitigating emerging COVID-19 clusters by conducting active nationwide epidemiological surveillance. However, an increasing number of cases appeared until early April, many with unclear infection routes exhibiting no recent history of travel outside Japan. We aimed to evaluate the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) genome sequences from COVID-19 cases until early April and characterise the genealogical networks to demonstrate possible routes of spread in Japan. MethodsNasopharyngeal specimens were collected from patients and a quantitative reverse transcription polymerase chain reaction testing for SARS-CoV-2 was performed. Positive RNA samples were subjected whole genome sequencing and a haplotype network analysis was performed. FindingsSome of the primary clusters identified during January and February in Japan directly descended from Wuhan-Hu-1-related isolates in China and other distinct clusters. Clusters were almost contained until mid-March; the haplotype network analysis demonstrated that COVID-19 cases from late March through early April may have caused an additional large cluster related to the outbreak in Europe, leading to additional spread within Japan. National self-restraint during February was effective in mitigating the COVID-19 spread, but late action on stopping immigration and declaring national emergency in Japan might be involved in the later increase in cases. InterpretationGenome surveillance suggested that at least two distinct SARS-CoV-2 introductions from China and other countries occurred. FundingJapan Agency for Medical Research and Development.
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The Diamond Princess (DP) cruise ship was put under quarantine offshore Yokohama, Japan, after a passenger who disembarked in Hong Kong was confirmed as a COVID-19 case. We performed whole genome sequencing of SARS-CoV-2 directly from PCR-positive clinical specimens and conducted a haplotype network analysis of the outbreak. All tested isolates exhibited a transversion at G11083T, suggesting that SARS-CoV-2 dissemination on the DP originated from a single introduction event before the quarantine started. Although further spreading might have been prevented by quarantine, some progeny clusters were linked to transmission through mass-gathering events in the recreational areas and direct transmission among passengers who shared cabins during the quarantine. This study demonstrates the usefulness of haplotype network analysis in identifying potential infection routes. One Sentence SummaryGenome-based tracing of SARS-CoV-2 infections among passengers and crews in Diamond Princess cruise ship during the quarantine
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ObjectiveTo identify common features of cases with novel coronavirus disease (COVID-19) so as to better understand what factors promote secondary transmission including superspreading events. MethodsA total of 110 cases were examined among eleven clusters and sporadic cases, and investigated who acquired infection from whom. The clusters included four in Tokyo and one each in Aichi, Fukuoka, Hokkaido, Ishikawa, Kanagawa and Wakayama prefectures. The number of secondary cases generated by each primary case was calculated using contact tracing data. ResultsOf the 110 cases examined, 27 (24.6%) were primary cases who generated secondary cases. The odds that a primary case transmitted COVID-19 in a closed environment was 18.7 times greater compared to an open-air environment (95% confidence interval [CI]: 6.0, 57.9). ConclusionsIt is plausible that closed environments contribute to secondary transmission of COVID-19 and promote superspreading events. Our findings are also consistent with the declining incidence of COVID-19 cases in China, as gathering in closed environments was prohibited in the wake of the rapid spread of the disease.
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A population-based cohort study on pediatric infectious diseases was established at Khanh Hoa Province, central Vietnam in 2006, to determine the etiology and risk factors for severe pediatric infectious diseases (SPID) such as acute respiratory infection (ARI), diarrhea and dengue which are the major causes of under 5 mortality. A population census survey was conducted in Nha-Trang and Ninh-Hoa to collect demographic, social-behavioral data and disease burden on SPID. The study site covered a population of 353,525 residing in 75,826 households with 24,781 children less than 5 years. Hospital databases from two hospitals covering the region were obtained. Linking the census and hospital databases, we were able to investigate on a variety of SPID such as environmental tobacco smoking exposure and increased risked of pediatric pneumonia hospitalization, population density, water supply and risk of dengue fever and animal livestock and risk of hospitalized diarrhea. To determine incidence, viral etiology and risk factors for pediatric ARI/pneumonia, we setup a population based prospective hospitalized Pediatric ARI surveillance at Khanh Hoa General Hospital, Nha-Trang in February 2007. The study has revealed RSV, rhinovirus and influenza A as major viral pathogens, role of multiple viral infection and its interaction with bacteria in the development of pneumonia. In addition, we are also conducting a birth cohort study to investigate the incidence of congenital infection and its impact on physical-neurological development, and role of host genetic polymorphism on SPID hospitalization in Vietnam. Population mobility, high cost of regular census update and low mortality are the challenges.
ABSTRACT
A population-based cohort study on pediatric infectious diseases was established at Khanh Hoa Province, central Vietnam in 2006, to determine the etiology and risk factors for severe pediatric infectious diseases (SPID) such as acute respiratory infection (ARI), diarrhea and dengue which are the major causes of under 5 mortality. A population census survey was conducted in Nha-Trang and Ninh-Hoa to collect demographic, social-behavioral data and disease burden on SPID. The study site covered a population of 353,525 residing in 75,826 households with 24,781 children less than 5 years. Hospital databases from two hospitals covering the region were obtained. Linking the census and hospital databases, we were able to investigate on a variety of SPID such as environmental tobacco smoking exposure and increased risked of pediatric pneumonia hospitalization, population density, water supply and risk of dengue fever and animal livestock and risk of hospitalized diarrhea. To determine incidence, viral etiology and risk factors for pediatric ARI/pneumonia, we setup a population based prospective hospitalized Pediatric ARI surveillance at Khanh Hoa General Hospital, Nha-Trang in February 2007. The study has revealed RSV, rhinovirus and influenza A as major viral pathogens, role of multiple viral infection and its interaction with bacteria in the development of pneumonia. In addition, we are also conducting a birth cohort study to investigate the incidence of congenital infection and its impact on physical-neurological development, and role of host genetic polymorphism on SPID hospitalization in Vietnam. Population mobility, high cost of regular census update and low mortality are the challenges.
ABSTRACT
A prospective case–control study was conducted in urban districts in Hanoi, northern Vietnam to evaluate the effect of migration on the risk of hospitalisation for dengue in a Vietnamese urban population. We enrolled laboratory-confirmed dengue patients aged >18 years who were hospitalised in local hospitals in November and December 2010. Four neighbourhood-matched controls for each case were recruited within a week of hospitalisation. Sociodemographic data were collected by interviews, and the number of immature and adult mosquitoes within household premises was counted by entomological survey. Matched-pair analyses were conducted using conditional logistic regression models. Among 43 cases and 168 controls, 84% and 83% were migrants from rural areas, respectively. Although statistical significance was marginal, recent migration (residing in study area for 6 years) did not change the risk (aOR = 1.1; 95% CI = 0.30–4.05). Younger age (18–34 years) (aOR = 7.26; 95% CI = 2.39–22.06) and higher adult Aedes aegypti infestation level within household premises (aOR = 9.25; 95% CI = 1.68–51.09) were also independently associated with hospitalisation for dengue. Recent migration from rural areas seems to increase the risk of hospitalisation for dengue in urban populations in endemic areas. Further research including cohort study should be done to confirm the impact of migration on the risk of dengue in urban areas.
