Diphtheria and tetanus immunity among blood donors in Toronto

OBJECTIVE: To determine the diphtheria and tetanus antitoxin levels among blood donors in Toronto. DESIGN: Cross-sectional seroprevalence study. SETTING: Two fixed-site blood-donation clinics in Toronto from September to November 1994. PARTICIPANTS: Blood donors 20 years of age or older were eligible to participate; of the 781 eligible donors, 710 (90.9%) participated in the study. MAIN OUTCOME MEASURES: Diphtheria and tetanus antitoxin levels and factors associated with disease susceptibility, such as vaccination history, country of birth, age and sex. A diphtheria antitoxin level lower than 0.01 lU/mL and a tetanus antitoxin level lower than 0.15 lU/mL were considered nonprotective. RESULTS: Among the participants, 147 (20.7%) had a diphtheria antitoxin level in the nonprotective range, and 124 (17.5%) had a tetanus antitoxin level that was nonprotective. Increasing age and lack of written vaccination records were associated with susceptibility to the 2 diseases. Birth outside Canada was significantly related to tetanus susceptibility. CONCLUSION: Adults over 50 years of age who did not know their vaccination history were the least likely to be protected against diphtheria and tetanus. The greatest benefit of any immunization strategy would be gained by targeting this group.     

Diphtheria-neutralizing antibody levels in healthy adults from Rio de Janeiro, Brazil

In Brazil, until 2004, the immunization policy against diphtheria involved childhood vaccination with no official routine booster dose administered after 15 years of age. This study assessed functional antibody levels against diphtheria among blood donors. A total of 140 blood samples were collected, and diphtheria antitoxin levels were evaluated by Vero cell neutralization test. The mean age of the population was 34 years old (range: 18-61 years); 37.8% females and 62.2% males. Overall, 30.7% (95%, CI: 23.4-38.7) individuals presented neutralizing antitoxin antibody titers < 0.01 IU/ml; 42.1% (95%, CI: 34.1-50.4) showed values between 0.01-0.09 IU/ml and, 27.1% (95%, CI: 20.2-34.9) had (3) 0.1 IU/ml. In the subgroup of individuals with history of diphtheria immunization during childhood (85%), a number of 28.5% showed unprotective levels of circulating neutralizing antibody (< 0.01 IU/ml). Despite the continuous progress of immunization programs directed to Brazilian population, currently healthy adults remain susceptible to diphtheria.     

Efficacy of pertussis vaccination in England. Report from the PHLS Epidemiological Research Laboratory and 21 area health authorities.

A national assessment of the efficacy of pertussis vaccination was made in 21 area health authorities in England. Notification rates for children given either three doses of diphtheria/tetanus/pertussis vaccine or diphtheria/tetanus vaccine were studied during the two and a half-year period January 1978-June 1980. A survey of home circumstances showed that the two vaccine groups could be validly compared. Home visits were made to assess the severity of the illness, the attack rates in home contacts, and to take pernasal swabs. Pertussis vaccination was found to be of outstanding value in preventing serious disease. Nevertheless, its effect in controlling whooping cough is limited by the fact that protection for home contacts is less satisfactory, and by the occurrence of mild cases in vaccinated children which may contribute to the spread of the disease.     

Yellow Fever Outbreaks in Unvaccinated Populations,Brazil, 2008–2009

Due to the risk of severe vaccine-associated adverse events, yellow fever vaccination in Brazil is only recommended in areas considered at risk for disease. From September 2008 through June 2009, two outbreaks of yellow fever in previously unvaccinated populations resulted in 21 confirmed cases with 9 deaths (case-fatality, 43%) in the southern state of Rio Grande do Sul and 28 cases with 11 deaths (39%) in Sao Paulo state. Epizootic deaths of non-human primates were reported before and during the outbreak. Over 5.5 million doses of yellow fever vaccine were administered in the two most affected states. Vaccine-associated adverse events were associated with six deaths due to acute viscerotropic disease (0.8 deaths per million doses administered) and 45 cases of acute neurotropic disease (5.6 per million doses administered). Yellow fever vaccine recommendations were revised to include areas in Brazil previously not considered at risk for yellow fever.     

The immunological efficacy of one, two and three inoculations against diphtheria in adults

The outbreak of diphtheria in the Republic of Belarus developed in the presence of a sharp deficiency of immunity among the population aged 35 years and over. In connection with a higher initial immunity level resulting from vaccination made in one injection the minimum antibody level (> or = 0.01 I.U./ml) was found in 79.7% of the examinees among the population under 35 years. For the age group of 35-60 years vaccination in one and two injections proved to be insufficiently effective (the minimum protective antibody titer was found, respectively, in 64.3% and 63.3% of the vaccinees). To achieve the full protection of this group of the population, vaccination in three injections was necessary; after that the minimum protective antibody titer was found in 90.7%, the protective antibody titer (0.1 I.U./ml) was found in 53.5% and the highly protective antibody titer (1.0 I.U./ml) was found in 11.6% of the examinees. The low level of highly protected persons among vaccinees receiving three injections was due to a low dose of diphtheria toxoid (2 Lf) in adsorbed DT-m vaccine with reduced antigen content.     

Immunisation of adults during an outbreak of diphtheria.

In an outbreak of infection due to Corynebacterium diphtheriae in a hospital for mentally subnormal adults sera from 211 members of staff were screened for diphtheria antitoxin titres. Of these, 79 (37%) required immunisation, and a low dose preparation (1 LfU of diphtheria and 10 LfU tetanus toxoids) was offered. Of the 64 subjects who accepted a single immunisation and were subsequently retested, seroconversion to diphtheria toxoid occurred in 45 (70%), the rate being highest in younger adults. Seroconversion to tetanus toxoid occurred in 59% of subjects. Local reactions to the single dose were reported by 29 (43%) subjects, and nine (13%) experienced moderately severe local reactions and systemic symptoms. We conclude that adults should not be vaccinated without previous screening for susceptibility to diphtheria; that neither previous immunisation nor age is reliable in predicting the need for vaccination; and that though a single booster dose of diphtheria toxoid is probably effective in adults under 45, two doses should be given to those in the older age group.     

Measles outbreak in 31 schools: risk factors for vaccine failure and evaluation of a selective revaccination strategy.

OBJECTIVE: To examine the risk factors for measles vaccine failure and to evaluate the effectiveness of a selective revaccination strategy during a measles outbreak. DESIGN: Matched case-control study. SETTING: Thirty-one schools in Mississauga, Ont. SUBJECTS: Eighty-seven previously vaccinated school-aged children with measles that met the Advisory Committee on Epidemiology''s clinical case definition for measles. Two previously vaccinated control subjects were randomly selected for each case subject from the same homeroom class. INTERVENTIONS: All susceptible contacts were vaccinated, and contacts who had been vaccinated before Jan. 1, 1980, were revaccinated. When two or more cases occurred in a school all children vaccinated before 1980 were revaccinated. MAIN OUTCOME MEASURES: Risk of measles associated with age at vaccination, time since vaccination, vaccination before 1980 and revaccination. RESULTS: Subjects vaccinated before 12 months of age were at greater risk of measles than those vaccinated later (adjusted odds ratio [OR] 7.7, 95% confidence interval [CI] 1.6 to 38.3; p = 0.01). Those vaccinated between 12 and 14 months of age were at no greater risk than those vaccinated at 15 months or over. Subjects vaccinated before 1980 were at greater risk than those vaccinated after 1980 (adjusted OR 14.5, 95% CI 1.5 to 135.6). Time since vaccination was not a risk factor. Revaccination was effective in reducing the risk of measles in both subjects vaccinated before 1980 and those vaccinated after 1980 (adjusted OR reduced to 0.6 [95% CI 0.1 to 5.3] and 0.3 [95% CI 0.13 to 2.6] respectively). However, only 18 cases were estimated to have been prevented by this strategy. CONCLUSIONS: Adherence to routine measles vaccination for all eligible children is important in ensuring appropriate coverage with a single dose. The selective revaccination strategy''s high labour intensiveness and low measles prevention rate during the outbreak bring into question the effectiveness of such a strategy.     

Revaccination of children during school-based measles outbreaks: potential impact of a new policy recommendation.

OBJECTIVE: To evaluate the potential impact of revaccination on measles outbreak control during school-based epidemics. DESIGN: Retrospective cohort study. SETTING: Thirty-two public elementary and high schools in 14 communities on the west island of Montreal. PARTICIPANTS: All 19,439 children attending these schools during the 1989 measles epidemic in Quebec. INTERVENTION: After notification of a case children with provider-verified records of vaccination on or after their first birthday were identified; the remaining children were vaccinated or excluded from school. OUTCOME MEASURE: Clinical or confirmed measles cases not prevented by this intervention that could have been prevented had revaccination been included during the outbreak. RESULTS: Of the 88 measles cases (74 confirmed) proof of one adequate vaccination was present in 48 (55%). Intervention generally occurred within 5 school days after case notification. The nonpreventable cases involved 75 children who had measles onset before the intervention and 11 (7 vaccinated) who had onset within 8 days after the intervention. The two remaining cases occurred 20 and 25 days after the intervention among nonvaccinated students who refused to be vaccinated. Except for these two cases measles was eliminated at every school. Application of the new Canadian guidelines for measles outbreak control would have required the administration of at least 10,000 additional doses during the outbreak to students vaccinated before 1980; implementation of the new US guidelines would have required the administration of 16,629 additional doses to children previously vaccinated only once. Well-enforced provincial regulations ensuring vaccination of every student upon school entry might have prevented 38 (43%) of the cases. The US recommendation of two routine doses of vaccine before school entry might have prevented 86 (98%) of the cases. However, revaccination during the outbreak would not have prevented a single additional case. CONCLUSION: Revaccination of previously vaccinated students during a measles outbreak would have been costly and of little benefit.     

An Outbreak of Cryptosporidium parvum across England & Scotland Associated with Consumption of Fresh Pre-Cut Salad Leaves,May 2012

BackgroundWe report a widespread foodborne outbreak of Cryptosporidium parvum in England and Scotland in May 2012. Cases were more common in female adults, and had no history of foreign travel. Over 300 excess cases were identified during the period of the outbreak. Speciation and microbiological typing revealed the outbreak strain to be C. parvum gp60 subtype IIaA15G2R1.MethodsHypothesis generation questionnaires were administered and an unmatched case control study was undertaken to test the hypotheses raised. Cases and controls were interviewed by telephone. Controls were selected using sequential digit dialling. Information was gathered on demographics, foods consumed and retailers where foods were purchased.ResultsSeventy-four laboratory confirmed cases and 74 controls were included in analyses. Infection was found to be strongly associated with the consumption of pre-cut mixed salad leaves sold by a single retailer. This is the largest documented outbreak of cryptosporidiosis attributed to a food vehicle.     

Characteristics of Hospitalized Cases of Pertussis in Catalonia and Navarra,Two Regions in the North of Spain

Pertussis causes a large number of cases and hospitalizations in Catalonia and Navarra. We made a study of household cases of pertussis during 2012 and 2013 in order to identify risk factors for hospitalization in pertussis cases. Each primary case reported triggered the study of their contacts. Close contacts at home and people who were in contact for >2 hours during the transmission period of cases were included. The adjusted OR and 95% confidence intervals (CI) was calculated using logistic regression. A total of 1124 pertussis cases were detected, of which 14.9% were hospitalized. Inspiratory whoop (aOR: 1.64; CI: 1.02–2.65), apnoea (aOR: 2.47; CI: 1.51–4.03) and cyanosis (aOR: 15.51; CI: 1.87–128.09) were more common in hospitalized than in outpatient cases. Hospitalization occurred in 8.7% of correctly-vaccinated cases, 41.1% of non-vaccinated cases and 9.4% of partially-vaccinated cases. In conclusion, inspiratory whoop, apnoea and cyanosis were associated factors to hospitalization while vaccination reduced hospitalizations due to pertussis.     

Outbreak of mumps virus genotype G infection in tribal individuals during 2016–17 in India

Tribal individuals presented with fever and uni‐ or bi‐lateral parotitis in Galonda and Silli villages (Dadra and Nagar Haveli, India) between 2 October 2016 and 19 March 2017. Consequently, the magnitude and epidemiological characteristics of the outbreak were investigated. Overall, 139 cases of suspected mumps were identified in both the above villages. Most of the suspected cases were 5–15 years old, the exceptions being three adults who had no noticeable complications. Specimens were collected from 42 of the suspected cases and their close contacts (n = 39) for laboratory investigation. Mumps infection was laboratory‐confirmed in 73.8% and 20.5% of the suspected cases and contacts, respectively. Mumps was confirmed in seven adults aged 17–42 years, including three suspected cases and four contacts. To the best of our knowledge, this is the first report of a complete virus genome circulating among tribal individuals. Sequencing and phylogenetic studies revealed circulation of mumps virus genotype G in these tribal villages with 99% identity to a mumps virus detected in the UK (1996) and Canada (2009). Comparison with Indian mumps viruses revealed 99% and 98% identity to previously reported isolates from Pune during 2012 and 1986, respectively. Although the outbreak was large, no major complications were reported in the tribal villages. Detection of asymptomatic mumps in numerous close contacts indicates the importance of laboratory investigations in an outbreak setting.

     

Epidémie de diphtérie survenue sur la C?te Nord du St-Laurent à l'automne de 1974

An outbreak of diphtheria occurred on the North Shore of the St. Lawrence River at the beginning of September 1974. It started with the death of an 18-year-old forest worker Sept. 5, spread over a vast area of the North Shore and lasted until the end of October that year. Eleven strains of toxigenic Corynebacterium diphtheriae intermedium, type K were isolated. Eleven of the 12 patients had characteristic diphtheritic pharyngitis with pseudomembranes. Preventive measures, set forth immediately after the third case was declared, included the following: (a) daily surveillance of all contacts, (b) isolation or preventive hospitalization of persons with all types of pharyngitis, (c) mass vaccination of all susceptible persons and (d) search for healthy carriers of the germ. No strains of toxigenic C. diptheriae were isolated from patients preventively hospitalized or from the 1235 individuals among whom carriers were sought. Among the main characteristics of this epidemic, the mean age of the patients (17 years), their mobility and their habits are factors that could have made it almost uncontrollable. It is also remarkable that this outbreak occurred in such a scattered population of adolescents, in 82% of whom the Schick test was negative.     

Cholera outbreak in Forcibly Displaced Myanmar National (FDMN) from a small population segment in Cox’s Bazar,Bangladesh, 2019

BackgroundBangladesh experienced a sudden, large influx of forcibly displaced persons from Myanmar in August 2017. A cholera outbreak occurred in the displaced population during September-December 2019. This study aims to describe the epidemiologic characteristics of cholera patients who were hospitalized in diarrhea treatment centers (DTCs) and sought care from settlements of Forcibly Displaced Myanmar Nationals (FDMN) as well as host country nationals during the cholera outbreak.MethodsDiarrhea Treatment Center (DTC) based surveillance was carried out among the FDMN and host population in Teknaf and Leda DTCs hospitalized for cholera during September-December 2019.ResultsDuring the study period, 147 individuals with cholera were hospitalized. The majority, 72% of patients reported to Leda DTC. Nearly 65% sought care from FDMN settlements. About 47% of the cholera individuals were children less than 5 years old and 42% were aged 15 years and more. Half of the cholera patients were females. FDMN often reported from Camp # 26 (45%), followed by Camp # 24 (36%), and Camp # 27 (12%). Eighty-two percent of the cholera patients reported watery diarrhea. Some or severe dehydration was observed in 65% of cholera individuals. Eighty-one percent of people with cholera received pre-packaged ORS at home. About 88% of FDMN cholera patients reported consumption of public tap water. Pit latrine without water seal was often used by FDMN cholera individuals (78%).ConclusionVigilance for cholera patients by routine surveillance, preparedness, and response readiness for surges and oral cholera vaccination campaigns can alleviate the threats of cholera.     

The diagnostic effectiveness of an immunoenzyme test system for determining diphtheria toxin antigens in the blood serum in a clinical laboratory trial

The data on the approbation of the diagnostic value of the enzyme immunoassay (EIA) system for the determination of diphtheria toxin in the blood sera of diphtheria patients and persons suspected for diphtheria are presented. The EIA system was prepared on the basis of F(ab)2 fractions of purified antidiphtheria antibodies. 240 serum samples from diphtheria and tonsillitis patients and from healthy persons were studied. Diphtheria toxin was determined in all patients with the toxic form of diphtheria and in 41.3% of patients with its localized forms. Blood was taken mainly of the first week of the disease. In healthy persons the results of EIA were negative. Thus, the trial of the assay system in a clinical laboratory showed its good diagnostic effectiveness. The use of this EIA system in medical practice is believed to be quite promising.     

Booster vaccination against tetanus and diphtheria: insufficient protection against diphtheria in young and elderly adults

We have recently demonstrated that single shot vaccinations against tetanus and diphtheria do not lead to long-lasting immunity against diphtheria in elderly persons despite administration at 5 year intervals. In the present study we have immunized a group of young adults against tetanus and diphtheria to compare the pre- and 28 days post-vaccination immune responses in the young group with results of the same vaccination performed in an elderly group of a previous study. We also studied protection in both groups 5 years after vaccination. We compared antibody titers at all three time points and also analyzed the T cell responses in both age groups 5 years after vaccination.Before vaccination 9 % of the elderly persons were not protected against tetanus, and 48 % did not have protection against diphtheria. In the young group all participants were protected against tetanus, but 52 % were also unprotected against diphtheria before vaccination. 28 days after vaccination 100 % of all participants had protective antibody concentrations against tetanus and only a small percentage in each age group (<10 %) was unprotected against diphtheria. 5 years later, 100 % of both cohorts were still protected against tetanus, but 24 % of the young and 54 % of the elderly group were unprotected against diphtheria. Antibody concentrations against diphtheria measured by ELISA correlated well with their neutralizing capacity. T cell responses to tetanus and diphtheria did not differ between young and old persons. We conclude that booster vaccinations against tetanus and diphtheria according to present recommendations provide long-lasting protection only against tetanus, but not against diphtheria, independently of age. In elderly persons, the level of protection is even lower, probably due to intrinsic age-related changes within the immune system and/or insufficient vaccination earlier in life.     

2017–2022年中国口蹄疫流行状况分析

【目的】分析近年来中国口蹄疫流行和传播特点,研判口蹄疫流行趋势。【方法】以2017-2022年间中国报告发生的口蹄疫疫情为研究对象,从疫情的“三间分布”、生产环节分布、流行毒株分子流行病学分析及溯源等方面,对近6年的疫情情况进行系统梳理。【结果】2017-2022年间中国共有15个省份报告发生口蹄疫疫情54次。总体形势稳定：Asia 1型口蹄疫维持无疫状态;2019-2022年连续4年未发生A型口蹄疫疫情;田间以散发O型口蹄疫为主。六年间报告牛口蹄疫疫情36次,羊疫情1次,猪疫情17次。分子流行病学研究表明,O/Mya-98、O/Ind-2001、O/CATHAY、O/PanAsia和A/Sea-97这5个流行毒株同时流行,且与同时期周边国家（缅甸、老挝和越南等）口蹄疫毒株遗传关系密切。流行病学调查结果显示,疫情（尤其是牛疫情,占比66.7%）主要发生在流通（57%）、散养（32%）等免疫薄弱环节。【结论】对内强化疫苗免疫和流通动物管控,对外严防境外毒株传入仍是今后中国口蹄疫防控的重要任务。     

Outbreak of Cutaneous Leishmaniasis among military personnel in French Guiana, 2020: Clinical,phylogenetic, individual and environmental aspects

BackgroundCutaneous Leishmaniasis (CL) is endemic in French Guiana but cases are usually sporadic. An outbreak signal was issued on May 15^th 2020 with 15 suspected cases after a military training course in the rainforest. An outbreak investigation was carried out.Methodology/Principal findingsThirty cases were confirmed. Leishmania guyanensis was the most frequent species (90%). The most frequent presentation was ulcerative (90%). Lesions on the face and hands were frequent (40% each). Eight cases (26%) presented a poor outcome after treatment with pentamidine and required a second line with amphotericin B. Three of them required further treatments with meglumine antimoniate or miltefosine. Two spots within the training area were deemed as likely sites of contamination, due to illegal logging. The isolated Leishmania strains did not form a separate cluster. Participation in Week 13 of year 2020 was associated with infection (OR = 4.59 [1.10–19.83]; p = 0.016) while undergoing only the “Fighting” exercise was protective (OR = 0.1 [0–0.74]; p = 0.021). There was no association between infection and other risk factors at the individual level. The attack rate of Regiment B (14/105 = 13.3%) was significantly higher (OR = 4.22 [1.84–9.53], p = 0.0001) compared to Regiment A (16/507 = 3.2%). The attack rate during this training course (30/858 = 3.5%) was significantly higher (OR 2.29 [1.28–4.13]; p = 0.002) than for other missions in French Guiana during the same period (22/1427 = 1.5%).ConclusionsThis outbreak could be explained by a combination of factors: climatic conditions around week 13, at-risk activities including night trainings, absence of impregnation, a lesser experience of rainforest duties in Regiment B and illegal logging attracting sandflies on military training grounds.     

Assessing the impact of preventive mass vaccination campaigns on yellow fever outbreaks in Africa: A population-level self-controlled case series study

BackgroundThe Eliminate Yellow fever Epidemics (EYE) strategy was launched in 2017 in response to the resurgence of yellow fever in Africa and the Americas. The strategy relies on several vaccination activities, including preventive mass vaccination campaigns (PMVCs). However, to what extent PMVCs are associated with a decreased risk of outbreak has not yet been quantified.Methods and findingsWe used the self-controlled case series (SCCS) method to assess the association between the occurrence of yellow fever outbreaks and the implementation of PMVCs at the province level in the African endemic region. As all time-invariant confounders are implicitly controlled for in the SCCS method, this method is an alternative to classical cohort or case–control study designs when the risk of residual confounding is high, in particular confounding by indication. The locations and dates of outbreaks were identified from international epidemiological records, and information on PMVCs was provided by coordinators of vaccination activities and international funders. The study sample consisted of provinces that were both affected by an outbreak and targeted for a PMVC between 2005 and 2018. We compared the incidence of outbreaks before and after the implementation of a PMVC. The sensitivity of our estimates to a range of assumptions was explored, and the results of the SCCS method were compared to those obtained through a retrospective cohort study design. We further derived the number of yellow fever outbreaks that have been prevented by PMVCs. The study sample consisted of 33 provinces from 11 African countries. Among these, the first outbreak occurred during the pre-PMVC period in 26 (79%) provinces, and during the post-PMVC period in 7 (21%) provinces. At the province level, the post-PMVC period was associated with an 86% reduction (95% CI 66% to 94%, p < 0.001) in the risk of outbreak as compared to the pre-PMVC period. This negative association between exposure to PMVCs and outbreak was robustly observed across a range of sensitivity analyses, especially when using quantitative estimates of vaccination coverage as an alternative exposure measure, or when varying the observation period. In contrast, the results of the cohort-style analyses were highly sensitive to the choice of covariates included in the model. Based on the SCCS results, we estimated that PMVCs were associated with a 34% (95% CI 22% to 45%) reduction in the number of outbreaks in Africa from 2005 to 2018. A limitation of our study is the fact that it does not account for potential time-varying confounders, such as changing environmental drivers of yellow fever and possibly improved disease surveillance.ConclusionsIn this study, we provide new empirical evidence of the high preventive impact of PMVCs on yellow fever outbreaks. This study illustrates that the SCCS method can be advantageously applied at the population level in order to evaluate a public health intervention.

In this cohort study, Kévin Jean and colleagues correlate lower risk of disease outbreaks with mass vaccination against yellow fever.     

Transmission and containment of the SARS-CoV-2 Delta variant of concern in Guangzhou,China: A population-based study

BackgroundThe first community transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant of concern (VOC) in Guangzhou, China occurred between May and June 2021. Herein, we describe the epidemiological characteristics of this outbreak and evaluate the implemented containment measures against this outbreak.Methodology/Principal findingsGuangzhou Center for Disease Control and Prevention provided the data on SARS-CoV-2 infections reported between 21 May and 24 June 2021. We estimated the incubation period distribution by fitting a gamma distribution to the data, while the serial interval distribution was estimated by fitting a normal distribution. The instantaneous effective reproductive number (R_t) was estimated to reflect the transmissibility of SARS-CoV-2. Clinical severity was compared for cases with different vaccination statuses using an ordinal regression model after controlling for age. Of the reported local cases, 7/153 (4.6%) were asymptomatic. The median incubation period was 6.02 (95% confidence interval [CI]: 5.42–6.71) days and the means of serial intervals decreased from 5.19 (95% CI: 4.29–6.11) to 3.78 (95% CI: 2.74–4.81) days. The incubation period increased with age (P<0.001). A hierarchical prevention and control strategy against COVID-19 was implemented in Guangzhou, with R_t decreasing from 6.83 (95% credible interval [CrI]: 3.98–10.44) for the 7-day time window ending on 27 May 2021 to below 1 for the time window ending on 8 June and thereafter. Individuals with partial or full vaccination schedules with BBIBP-CorV or CoronaVac accounted for 15.3% of the COVID-19 cases. Clinical symptoms were milder in partially or fully vaccinated cases than in unvaccinated cases (odds ratio [OR] = 0.26 [95% CI: 0.07–0.94]).Conclusions/SignificanceThe hierarchical prevention and control strategy against COVID-19 in Guangzhou was timely and effective. Authorised inactivated vaccines are likely to contribute to reducing the probability of developing severe disease. Our findings have important implications for the containment of COVID-19.