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We investigated 68 respiratory specimens from 35 coronavirus disease patients in Hong Kong, of whom 32 had mild disease. We found that severe acute respiratory syndrome coronavirus 2 and subgenomic RNA were rarely detectable beyond 8 days after onset of illness. However, virus RNA was detectable for many weeks by reverse transcription PCR.

Zoonotic and pandemic influenza continue to pose threats to global public health. Pandemics arise when novel influenza A viruses, derived in whole or in part from animal or avian influenza viruses, adapt to transmit efficiently in a human population that has little population immunity to contain its onward transmission. Viruses of previous pandemic concern, such as influenza A(H7N9), arose from influenza A(H9N2) viruses established in domestic poultry acquiring a hemagglutinin and neuraminidase from influenza A viruses of aquatic waterfowl. We report a novel influenza A(H3N8) virus in chicken that has emerged in a similar manner and that has been recently reported to cause zoonotic disease. Although they are H3 subtype, these avian viruses are antigenically distant from contemporary human influenza A(H3N2) viruses, and there is little cross-reactive immunity in the human population. It is essential to heighten surveillance for these avian A(H3N8) viruses in poultry and in humans.

The infectivity of severe acute respiratory syndrome coronavirus 2 in deceased persons and organisms remains unclear. We studied transgenic K18 hACE2 mice to determine the kinetics of virus infectivity after host death. Five days after death, virus infectivity in the lung declined by >96% and RNA copies declined by 48.2%.

Human infection with avian influenza A(H3N8) virus is uncommon but can lead to acute respiratory distress syndrome. In explant cultures of the human bronchus and lung, novel H3N8 virus showed limited replication efficiency in bronchial and lung tissue but had a higher replication than avian H3N8 virus in lung tissue.

We detected Middle East respiratory syndrome coronavirus (MERS-CoV) RNA in 305/1,131 (27%) camels tested at an abattoir in Al Hasa, Eastern Province, Saudi Arabia, during January 2016-March 2018. We characterized 48 full-length MERS-CoV genomes and noted the viruses clustered in MERS-CoV lineage 5 clade B.

We detected high titers of cross-reactive neuraminidase inhibition antibodies to influenza A(H5N1) virus clade 2.3.4.4b in 96.8% (61/63) of serum samples from healthy adults in Hong Kong in 2020. In contrast, antibodies at low titers were detected in 42% (21/50) of serum samples collected in 2009. Influenza A(H1N1)pdm09 and A(H5N1) titers were correlated.

We aimed to estimate SARS-CoV-2 vaccine effectiveness (VE) against medically attended SARS-CoV-2 infection in Hong Kong. We conducted a test-negative design study in individuals aged 5–64 years who presented with recent-onset (≤3 days) acute respiratory illness from April 2023 through to August 2024. Vaccination was defined as receipt of SARS-CoV-2 vaccine within 6 months of medical presentation, and for a sensitivity analysis, within 12 months of medical presentation. VE against laboratory-confirmed SARS-CoV-2 infection was estimated separately for 5–17-year-olds and 18–64-year-olds by conditional logistic regression adjusted for potential confounders. Within the age groups, there was no statistically significant difference in vaccination (within 6 months of medical presentation) proportions between cases and controls across strata of the assessed individual sociodemographic and health-related characteristics. A moderate VE of 64 % (95 % confidence interval, CI: 9–83 %) and 54 % (95 % CI: −39 to 77 %) was estimated in 5–17-year-olds and 18–64-year-olds, respectively. However, a higher VE of 85 % (95 % CI: 32–97 %) and a moderate VE of 59 % (95 % CI: 2–83 %) were estimated in 5–17-year-olds for mRNA and inactivated vaccines, respectively, although non-statistically significantly different (p = 0.33) whereas a lower VE of 29 % (95 % CI: −81 to 73 %) and a higher VE of 70 % (95 % CI: −5 to 92 %) were estimated in 18–64-year-olds for mRNA and inactivated vaccines, respectively, which were not statistically significantly different from each other (p = 0.38). VE estimates were higher for those who had had a previous SARS-CoV-2 infection compared with those who had not. VE was also higher in 5–17-year-olds who had self-tested for SARS-CoV-2 infection before medical presentation and lower in those who had not, whereas the opposite was observed in 18–64-year-olds. SARS-CoV-2 vaccines provided substantial protection against medically attended SARS-CoV-2 infection in both children and adults in Hong Kong. •SARS-CoV-2 VE was in the range 9–83 % and −39 to 77 % in 5–17-year-olds and 18–64-year-olds, respectively.•VE was higher for mRNA than inactivated vaccines in 5–17-year-olds, but higher for inactivated than mRNA vaccines in 18–64-year-olds; albeit, with substantial overlap of the confidence intervals.•VE was higher in those who had a previous SARS-CoV-2 infection compared with those who had not.•SARS-CoV-2 vaccines appeared to have conferred limited benefit to recipients who had not had a previous SARS-CoV-2 infection.•VE was higher in 5–17-year-olds who had self-tested and lower in those who had not whereas the opposite was observed in 18–64-year-olds.

We studied 2780 adults in Hong Kong who received CoronaVac inactivated virus vaccine (Sinovac) and BNT162b2 mRNA vaccine (“Comirnaty”, BioNTech/Fosun Pharma). We compared rates of antibody waning over time using an enzyme-linked immunosorbent assay for spike receptor binding domain and a surrogate virus neutralization test. We found stronger and more durable antibody responses to two doses of the mRNA vaccine, and slightly stronger initial antibody responses to each vaccine in younger adults and women. The weaker and less durable responses following CoronaVac support earlier provision of third doses to persons who previously received two doses of this vaccine.

In March 2020, mild signs and symptoms of coronavirus disease developed in a healthy 33-year-old man in Hong Kong. His first infection did not produce virus neutralizing antibodies. In August, he had asymptomatic reinfection, suggesting that persons without a robust neutralizing antibody response might be at risk for reinfection.