Incidence of influenza virus infections in children in Hong Kong in a 3-year randomized placebo-controlled vaccine study, 2009-2012.

BACKGROUND: School-aged children suffer high rates of influenza virus infections and associated illnesses each year, and are a major source of transmission in the community. However, information on the cumulative incidence of infection in specific epidemics is scarce, and there are limited studies with sufficient follow-up to identify the strength and duration of protection against reinfection. METHODS: We randomly allocated children 5-17 years of age to receive trivalent inactivated influenza vaccine (TIV) or placebo from September 2009 through January 2010, and then conducted follow-up for 3 years including regular collection of sera, symptom diaries, and collection of nose and throat swabs during illness episodes in participants or their household members. RESULTS: Of 796 children initially randomized, 484 continued to participate for all 3 years. In unvaccinated children, cumulative incidence of infection was estimated to be 59% in the first wave of H1N1pdm09 in 2009-2010, and 7%, 14%, 20%, and 31% in subsequent epidemics of H3N2 (2010), H1N1pdm09 (2011), B (2012), and H3N2 (2012), respectively. Infection with H1N1pdm09 in 2009-2010 and H3N2 in 2010 was associated with protection against infection with subsequent epidemics of the same subtype in 2011 and 2012, respectively, but we found no evidence of heterotypic or heterosubtypic protection against infection. CONCLUSIONS: We identified substantial incidence of influenza virus infections in children in Hong Kong in 5 major epidemics over a 3-year period, and evidence of homosubtypic but not heterosubtypic protection following infection. CLINICAL TRIALS REGISTRATION: NCT00792051.

Protective efficacy against pandemic influenza of seasonal influenza vaccination in children in Hong Kong: a randomized controlled trial.

BACKGROUND: The efficacy of seasonal influenza vaccination against 2009 pandemic influenza A(H1N1) remains unclear. METHODS: One child aged 6-17 years in each of 796 households was randomized to receive 2009-2010 seasonal trivalent inactivated influenza vaccine (TIV) or saline placebo between August 2009 and February 2010. Households were followed up with serology, symptom diaries, and collection of respiratory specimens during illnesses. The primary outcomes were influenza infection confirmed by reverse-transcription polymerase chain reaction (RT-PCR) or a ≥4-fold rise in serum antibody titer measured by hemagglutination inhibition assay. RESULTS: Receipt of TIV led to 8-13-fold mean geometric rises in antibody titers against seasonal A and B viruses, but only 1.5-fold mean geometric rises against the pandemic A(H1N1) virus that was not included in the vaccine. Children who received TIV had a reduced risk of seasonal influenza B confirmed by RT-PCR, with a vaccine efficacy estimate of 66% (95% confidence interval [CI], 31%-83%). Children who received TIV also a had reduced risk of pandemic influenza A(H1N1) indicated by serology, with a vaccine efficacy estimate of 47% (95% CI, 15%-67%). CONCLUSIONS: Seasonal TIV prevented pandemic influenza A(H1N1) and influenza B infections in children. Pandemic A(H1N1) circulated at the time of vaccination and for a short time afterward with no substantial seasonal influenza activity during that period. The potential mechanism for seasonal TIV to provide protection, possibly short lived, for children against pandemic A(H1N1) infection despite poor cross-reactive serologic response deserves further investigation. Clinical Trials Registration. NCT00792051.

Protective efficacy of seasonal influenza vaccination against seasonal and pandemic influenza virus infection during 2009 in Hong Kong.

BACKGROUND: The relationship between seasonal influenza vaccine and susceptibility to 2009 pandemic A/H1N1 virus infection is not fully understood. METHODS: One child 6-15 years of age from each of 119 households was randomized to receive 1 dose of inactivated trivalent seasonal influenza vaccine (TIV) or saline placebo in November 2008. Serum samples were collected from study subjects and their household contacts before and 1 month after vaccination (December 2008), after winter (April 2009) and summer influenza (September-October 2009) seasons. Seasonal and pandemic influenza were confirmed by serum hemagglutinination inhibition, viral neutralization titers, and reverse-transcription polymerase chain reaction performed on nasal and throat swab samples collected during illness episodes. RESULTS: TIV recipients had lower rates of serologically confirmed seasonal A/H1N1 infection (TIV group, 8%; placebo group, 21%; P=.10) and A/H3N2 infection (7% vs 12%; P=A9), but higher rates of pandemic A/H1N1 infection (32% vs 17%; [Formula: see text]). In multivariable analysis, those infected with seasonal influenza A during the study had a lower risk of laboratory-confirmed pandemic A/H1N1 infection (adjusted odds ratio [OR], 0.35; 95% confidence interval [CI], 0.14-0.87), and receipt of seasonal TIV was unassociated with risk of pandemic A/H1N1 infection (adjusted OR, 1.11; 95% CI, 0.54-2.26). CONCLUSIONS: TIV protected against strain-matched infection in children. Seasonal influenza infection appeared to confer cross-protection against pandemic influenza. Whether prior seasonal influenza vaccination affects the risk of infection with the pandemic strain requires additional study. CLINICAL TRIALS REGISTRATION: ClinicalTrials.gov number NCT00792051 .

Facemasks and hand hygiene to prevent influenza transmission in households: a cluster randomized trial.

BACKGROUND: Few data are available about the effectiveness of nonpharmaceutical interventions for preventing influenza virus transmission. OBJECTIVE: To investigate whether hand hygiene and use of facemasks prevents household transmission of influenza. DESIGN: Cluster randomized, controlled trial. Randomization was computer generated; allocation was concealed from treating physicians and clinics and implemented by study nurses at the time of the initial household visit. Participants and personnel administering the interventions were not blinded to group assignment. (ClinicalTrials.gov registration number: NCT00425893) SETTING: Households in Hong Kong. PATIENTS: 407 people presenting to outpatient clinics with influenza-like illness who were positive for influenza A or B virus by rapid testing (index patients) and 794 household members (contacts) in 259 households. INTERVENTION: Lifestyle education (control) (134 households), hand hygiene (136 households), or surgical facemasks plus hand hygiene (137 households) for all household members. MEASUREMENTS: Influenza virus infection in contacts, as confirmed by reverse-transcription polymerase chain reaction (RT-PCR) or diagnosed clinically after 7 days. RESULTS: Sixty (8%) contacts in the 259 households had RT-PCR-confirmed influenza virus infection in the 7 days after intervention. Hand hygiene with or without facemasks seemed to reduce influenza transmission, but the differences compared with the control group were not significant. In 154 households in which interventions were implemented within 36 hours of symptom onset in the index patient, transmission of RT-PCR-confirmed infection seemed reduced, an effect attributable to fewer infections among participants using facemasks plus hand hygiene (adjusted odds ratio, 0.33 [95% CI, 0.13 to 0.87]). Adherence to interventions varied. LIMITATION: The delay from index patient symptom onset to intervention and variable adherence may have mitigated intervention effectiveness. CONCLUSION: Hand hygiene and facemasks seemed to prevent household transmission of influenza virus when implemented within 36 hours of index patient symptom onset. These findings suggest that nonpharmaceutical interventions are important for mitigation of pandemic and interpandemic influenza. PRIMARY FUNDING SOURCE: Centers for Disease Control and Prevention.

A superspreading event involving a cluster of 14 coronavirus disease 2019 (COVID-19) infections from a family gathering in Hong Kong Special Administrative Region SAR (China).

OBJECTIVE: An outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in Wuhan, China, in December 2019, with subsequent spread around the world. Hong Kong Special Administrative Region SAR (China) recorded its first confirmed cases on 23 January 2020. In this report, we describe a family cluster of 12 confirmed cases, with two additional confirmed cases from secondary transmission. METHODS: We reported the epidemiological, clinical and laboratory findings of the family cluster, as well as the public health measures instituted. RESULTS: All 12 confirmed COVID-19 cases were among the 19 attendees of a three-hour Chinese New Year family dinner consisting of hotpot and barbecue dishes. Environmental sampling of the gathering venue was negative. Two additional confirmed cases, who were co-workers of two confirmed cases, were later identified, indicating secondary transmission. Contact tracing, quarantine and environmental disinfection were instituted to contain further spread. DISCUSSION: Our findings were highly suggestive of a superspreading event during the family gathering. The source was likely one of the cases during the pre-symptomatic phase. The event attested to the high infectivity of SARS-CoV-2 through human-to-human transmission from social activities and argued for the necessity of social distancing in curtailing the disease spread.

The epidemiology of COVID-19 cases and the successful containment strategy in Hong Kong-January to May 2020.

BACKGROUND: Hong Kong, a Special Administrative Region of China, recorded its first confirmed coronavirus disease 2019 (COVID-19) case on 23 January 2020. We reviewed the case epidemiology and the various public health measures implemented from January to May 2020. METHODS: The epidemiological and clinical characteristics of the cases recorded in different phases of the epidemic were described and compared, and the effectiveness of the public health measures implemented were reviewed using the changes in the daily number of confirmed cases and the interval from symptom onset to hospital admission. RESULTS: Between January and May 2020, 1084 confirmed COVID-19 cases were reported, about 70% of which had a history of travel during the incubation period. The case fatality ratio was 0.4%. The local epidemic progressed through four phases: (1) preparedness and imported infection from mainland China, (2) local transmission, (3) imported infection from overseas countries associated with local transmission, and (4) controlled imported infection with limited local transmission, with an eventual reduction of the daily case number and minimization of the onset-to-admission interval. Various public health measures, including enhanced surveillance, border control, and social distancing, were introduced in phases in response to the prevailing local and global situations. DISCUSSION: The overall containment strategy in Hong Kong led to a stabilization of the number of cases and the absence of a community-wide outbreak during the 4.5 m after the first case was reported. This strategy of containment might serve as an example for future planning of preparedness and response against novel infectious agents.

Review of vector-borne diseases in Hong Kong.

The epidemiology of vector-borne diseases in Hong Kong has changed over the past decade but still poses a significant public health risk. We provided a comprehensive review of the epidemiological information and analysed the trends of major vector-borne diseases, including the vector situation in Hong Kong. The incidence of malaria has dropped dramatically in the past few decades and is now mainly an imported disease acquired from malaria endemic countries. Locally acquired dengue fever occurred in 2002 and 2003, and thereafter all cases were imported, mainly from Southeast Asia areas. Only a few local cases of Japanese encephalitis were reported in the past decade. In contrast, there is a notable increase in scrub typhus and spotted fever cases. The emergence of chikungunya fever in Asia and Indian Ocean countries also resulted in importation of human cases. Given the heavy traffic between this international city and other parts of the world, as well as the presence of vectors in this densely populated area, vigilance should be maintained against these infections. Comprehensive public health measures encompassing disease surveillance, vector surveillance and control measures with support from all sectors of the community are required to combat the old and newly emerging vector-borne diseases in Hong Kong.

A superspreading event involving a cluster of 14 coronavirus disease 2019 (COVID-19) infections from a family gathering in Hong Kong SAR (China)

@#Objective: An outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in Wuhan, China, in December 2019, with subsequent spread around the world. Hong Kong Special Administrative Region SAR (China) recorded its first confirmed cases on 23 January 2020. In this report, we describe a family cluster of 12 confirmed cases, with two additional confirmed cases from secondary transmission. Methods: We reported the epidemiological, clinical and laboratory findings of the family cluster, as well as the public health measures instituted. Results: All 12 confirmed COVID-19 cases were among the 19 attendees of a three-hour Chinese New Year family dinner consisting of hotpot and barbecue dishes. Environmental sampling of the gathering venue was negative. Two additional confirmed cases, who were co-workers of two confirmed cases, were later identified, indicating secondary transmission. Contact tracing, quarantine and environmental disinfection were instituted to contain further spread. Discussion: Our findings were highly suggestive of a superspreading event during the family gathering. The source was likely one of the cases during the pre-symptomatic phase. The event attested to the high infectivity of SARS-CoV-2 through human-to-human transmission from social activities and argued for the necessity of social distancing in curtailing the disease spread.