A range of public health measures have been implemented to suppress local transmission of coronavirus disease 2019 (COVID-19) in Hong Kong. We examined the effect of these interventions and behavioural changes of the public on the incidence of COVID-19, as well as on influenza virus infections, which might share some aspects of transmission dynamics with COVID-19. We analysed data on laboratory-confirmed COVID-19 cases, influenza surveillance data in outpatients of all ages, and influenza hospitalisations in children. We estimated the daily effective reproduction number (Rt) for COVID-19 and influenza A H1N1 to estimate changes in transmissibility over time. Attitudes towards COVID-19 and changes in population behaviours were reviewed through three telephone surveys done on Jan 20-23, Feb 11-14, and March 10-13, 2020. COVID-19 transmissibility measured by Rt has remained at approximately 1 for 8 weeks in Hong Kong. Influenza transmission declined substantially after the implementation of social distancing measures and changes in population behaviours in late January, with a 44% (95% CI 34-53%) reduction in transmissibility in the community, from an estimated Rt of 1·28 (95% CI 1·26-1·30) before the start of the school closures to 0·72 (0·70-0·74) during the closure weeks. Similarly, a 33% (24-43%) reduction in transmissibility was seen based on paediatric hospitalisation rates, from an Rt of 1·10 (1·06-1·12) before the start of the school closures to 0·73 (0·68-0·77) after school closures. Among respondents to the surveys, 74·5%, 97·5%, and 98·8% reported wearing masks when going out, and 61·3%, 90·2%, and 85·1% reported avoiding crowded places in surveys 1 (n=1008), 2 (n=1000), and 3 (n=1005), respectively. Our study shows that non-pharmaceutical interventions (including border restrictions, quarantine and isolation, distancing, and changes in population behaviour) were associated with reduced transmission of COVID-19 in Hong Kong, and are also likely to have substantially reduced influenza transmission in early February, 2020. Health and Medical Research Fund, Hong Kong.

Viral shedding profile of infections caused by the pandemic H1N1 2009 influenza A virus has not been reported. The aim of this study was to determine the viral load in different body sites. Viral loads of pandemic H1N1 virus in respiratory specimens, stool, urine, and serum were determined by quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR). Respiratory specimens from patients with seasonal influenza were used as historical controls. Initial pre‐treatment viral load were compared between these two groups. Serial respiratory specimens from patients with pandemic H1N1 virus infection were obtained for analysis of viral dynamics. Twenty‐two pandemic H1N1 cases and 44 seasonal influenza historical controls were included. The mean initial viral load before oseltamivir therapy was 1.84 × 10⁸ copies/ml for pandemic H1N1 virus compared with 3.28 × 10⁸ copies/ml in seasonal influenza historical controls (P = 0.085). Among patients with pandemic H1N1 virus infection, peak viral load occurred on the day of onset of symptoms, and declined gradually afterwards, with no virus being detectable in respiratory specimens by RT‐PCR 8 days and by culture 5 days after the onset of symptoms respectively, except in one patient. Pandemic H1N1 virus was detected in stool and in urine from 4/9 and 1/14 patients, respectively. Viral culture was also positive from the stool sample with the highest viral load. Younger age was associated with prolonged shedding in the respiratory tract and higher viral load in the stool. Data from this quantitative analysis of viral shedding may have implications for formulating infection control measures. J. Med. Virol. 82:1–7, 2010.

SARS-CoV-2 infection of children leads to a mild illness and the immunological differences with adults are unclear. Here, we report SARS-CoV-2 specific T cell responses in infected adults and children and find that the acute and memory CD4⁺ T cell responses to structural SARS-CoV-2 proteins increase with age, whereas CD8⁺ T cell responses increase with time post-infection. Infected children have lower CD4⁺ and CD8⁺ T cell responses to SARS-CoV-2 structural and ORF1ab proteins when compared with infected adults, comparable T cell polyfunctionality and reduced CD4⁺ T cell effector memory. Compared with adults, children have lower levels of antibodies to β-coronaviruses, indicating differing baseline immunity. Total T follicular helper responses are increased, whilst monocyte numbers are reduced, indicating rapid adaptive co-ordination of the T and B cell responses and differing levels of inflammation. Therefore, reduced prior β-coronavirus immunity and reduced T cell activation in children might drive milder COVID-19 pathogenesis.

Objective. To study the epidemiologic, clinical, laboratory, and radiologic features, prognostic indicators, and short-term to medium-term outcomes for children with severe acute respiratory syndrome (SARS) and to validate the performance characteristics of a clinical case definition, calculated with respect to SARS-associated coronavirus (SARS-CoV) seroconversion.Methods. Children <18 years of age, from a single-site outbreak, who satisfied a clinical case definition for SARS, with subsequent serologic confirmation, were treated according to a standard protocol and prospectively monitored.Results. Forty-four children were included. The median age was 12 years. Forty-two children (95.5%) demonstrated an epidemiologic link. Fever, cough, malaise, coryza, sputum production, headache, myalgia, lymphopenia, and elevated lactate dehydrogenase levels were common presenting features. Radiographic findings were nonspecific, but high-resolution computed tomography of the thorax was an early diagnostic aid. A specific reverse transcription-polymerase chain reaction assay for SARS-CoV yielded positive results for 12 years was associated with methylprednisolone therapy for severe illness. After exclusion of the only infant, an age of >12 years was associated with oxygen requirements. Sore throat, high neutrophil count at presentation, and peak neutrophilia were independent factors predicting severe illness. The clinical case definition demonstrated good sensitivity, specificity, and positive and negative predictive values (97.8%, 92.7%, 88%, and 98.7%, respectively) for diagnostic accuracy.Conclusions. Children are susceptible to SARS-CoV infection. Teenagers resemble adults with respect to disease progression and may develop severe illness. The short-term to medium-term outcomes are good. Sore throat and initial and peak neutrophilia seem to be predictors of severe illness. Our clinical case definition performed well in the epidemic.

Background: Clinical management of shrimp allergy is hampered by the lack of accurate tests. Molecular diagnosis has been shown to more accurately reflect the clinical reactivity but the full spectrum of shrimp allergens and their clinical relevance are yet to be established. We therefore sought to comprehend the allergen repertoire of shrimp, investigate and compare the sensitization pattern and diagnostic value of the allergens in allergic subjects of two distinct populations.Methods: Sera were collected from 85 subjects with challenge‐proven or doctor‐diagnosed shrimp allergy in Hong Kong and Thailand. The IgE‐binding proteins of Penaeus monodon were probed by Western blotting and identified by mass spectrometry. Recombinant shrimp allergens were synthesized and analyzed for IgE sensitization by ELISA.Results: Ten IgE‐binding proteins were identified, and a comprehensive panel of 11 recombinant shrimp allergens was generated. The major shrimp allergens among Hong Kong subjects were troponin C (Pen m 6) and glycogen phosphorylase (Pen m 14, 47.1%), tropomyosin (Pen m 1, 41.2%) and sarcoplasmic‐calcium binding protein (Pen m 4, 35.3%), while those among Thai subjects were Pen m 1 (68.8%), Pen m 6 (50.0%) and fatty acid‐binding protein (Pen m 13, 37.5%). Component‐based tests yielded significantly higher area under curve values (0.77–0.96) than shrimp extract‐IgE test (0.70–0.75). Yet the best component test differed between populations; Pen m 1‐IgE test added diagnostic value only in the Thai cohort, whereas sensitizations to other components were better predictors of shrimp allergy in Hong Kong patients.Conclusion: Pen m 14 was identified as a novel shrimp allergen predictive of challenge outcome. Molecular diagnosis better predicts shrimp allergy than conventional tests, but the relevant component is population dependent.

The novel SARS-CoV-2 Omicron variant may increase the risk of reinfection and vaccine breakthrough infections as it possesses key mutations in the spike protein that affect neutralizing antibody response. Most studies on neutralization susceptibility were conducted using specimens from adult COVID-19 patients or vaccine recipients. However, since the pediatric population has an antibody response to SARS-CoV-2 infection that is distinct from the adult population, it is critical to assess the neutralization susceptibility of pediatric serum specimens. This study compared the neutralization susceptibility of serum specimens collected from 49 individuals of <18 years old, including 34 adolescent BNT162b2 (Pfizer-BioNTech) vaccine recipients, and 15 recovered COVID-19 patients aged between 2 and 17. We demonstrated that only 38.2% of BNT162b2 vaccine recipients and 26.7% of recovered COVID-19 patients had their serum neutralization titer at or above the detection threshold in our live virus microneutralization assay. Furthermore, the neutralizing antibody titer against Omicron variant was substantially lower than those against the ancestral virus or the Beta variant. Our results suggest that vaccine recipients and COVID-19 patients in the pediatric age group will likely be more susceptible to vaccine breakthrough infections or reinfections due to Omicron variant.