The effect of seasonal influenza vaccine on medically-attended influenza and non-influenza respiratory viruses infections at primary care level, Hong Kong SAR, 2017/18 to 2019/20.

Effectiveness of seasonal influenza vaccine (SIV) varies with the degree of matching with the vaccine and circulating viruses. We continued our SIV effectiveness against medically-attended influenza-like illness (ILI) under the Department of Health Hong Kong's sentinel private medical practitioners (PMP) network, using the test-negative case-control design, for the 2018/19 and 2019/20 season. In addition, we studied the potential interference between SIV and ILI caused by non-influenza respiratory viruses (NIRV) based on data collated from 2017/18 to 2019/20 seasons. 3404 patients were analysed. Across the 2017/18 to 2019/20 seasons, the vaccine effectiveness (VE) of SIV was 44% (95% CI 30-56%) against pan-negative controls, 57% (95%CI. 42-68%) against NIRV controls and 50% (95%CI 38-59%) against both. SIV was moderately effective against medically-attended ILI caused by influenza A/B in both 2018/19 and 2019/20 winter seasons (53.2% (95%CI 36.7-65.5%) and 41.8% (95%CI 6.3-64.1%), respectively). The VE against the main circulating subtype, influenza A(H1), was higher for the 2018/19 season (57.2% (95%CI 39.8-69.9%), compared to 34.6% (95%CI -9.6-61.4%) in the 2019/20 season). When compared to pan negative controls, those with single NIRV infections were similarly likely to have received SIV (OR 1.05 (95%CI 0.72-1.54) within the influenza season; OR 0.97 (95%CI 0.73-1.29) when including non-influenza seasons). Analyses by type of virus showed no increased risk of SIV identified among those with single infections of EV/RV, HMPV and parainfluenza but a 2-fold increased risk was shown for those with single infections of adenovirus and parainfluenza virus (adenovirus: OR 2.54 (95%CI 1.24-5.14) within influenza season and OR 1.78 (95%CI 1.01-3.09) for the whole period; parainfluenza virus: OR 2.01 (95%CI 1.22-3.29) within influenza season and OR 1.89 (95%CI 1.29-2.76) for the whole period). SIV programme and surveillance of influenza and NIRV, including SARS-CoV-2, should continue during the COVID-19 pandemic.

Varicella vaccine dose depended effectiveness and waning among preschool children in Hong Kong.

In Hong Kong, universal varicella vaccination was introduced in July 2014 with a two-dose schedule but the vaccines had been available in the private market since 1996. With data from varicella notification and surveys on immunization coverage, we used the screening method to estimate dose-specific varicella vaccine effectiveness (VE) among preschool children in Hong Kong before universal vaccination. We estimated the VE of one- and two-dose varicella vaccination against all notified varicella as 69.4% (95% confidence interval (95% CI) 69.5-71.2) and 93.4% (95% CI 91.7-94.7), respectively. We found that VE did not decrease with time since receipt. Varicella vaccine was more effective against complications (85.4% [95% CI 48.8-95.8] for one dose and 100% [95% CI -Inf to 100] for two doses) and against hospital admission (75.2% [95% CI 53.4-86.8] for one dose and 93.1% [95% CI 47.1-99.1] for two doses). Lower protection of one-dose varicella vaccine resulted in breakthrough varicella. Under universal vaccination, second-dose varicella vaccine (given as combined measles, mumps, rubella and varicella vaccine) was first scheduled for children when they reach primary one (about 6 years of age) and was recently advanced to 18 months of age. Shortening the interval between the first dose and second dose of varicella vaccination should reduce breakthrough varicella and outbreaks in preschool.

Seasonal influenza vaccine effectiveness at primary care level, Hong Kong SAR, 2017/2018 winter.

The 2017/18 winter influenza season in Hong Kong started in early January 2018, predominated by influenza B/Yamagata. We collaborated with private medical practitioners of our sentinel surveillance system to collect respiratory specimens and clinical information from patients with influenza-like illness for estimation of the influenza vaccine effectiveness (VE) using the test-negative case-control design. We found that the overall VE was 59.1% (95%CI 41.1 to 71.8%) against all influenza and 53.5% (95%CI 35.4 to 74.6%) against influenza B. Seasonal influenza vaccine provided moderate to good protection against laboratory-confirmed influenza infection at primary care level in Hong Kong in the 2017/18 winter influenza season.

An outbreak of community-associated methicillin-resistant Staphylococcus aureus infection in a boarding school in Hong Kong Special Administrative Region (China)

Background：In November 2012, an outbreak of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) skin and soft tissue infections affecting students at a boarding school in Hong Kong Special Administrative Region (China) was detected.Methods：A case was defined as any student or staff notified with MRSA infection from 25 October 2012 to 5 July 2013 with the clinical isolate being of staphylococcal cassette chromosome mec type IV or V and positive for Panton-Valentine leukocidin gene. We conducted field investigations, advised on control measures and enhanced surveillance for skin and soft tissue infections at the school. Decolonization therapies were offered to all cases and contacts, and carrier screening was conducted.Results：There were five cases; two (40%) were hospitalized and three (60%) required surgical treatments. Initial screening comprised 240 students and 81 staff members. Overall, four cases (80%) plus eight other students (3.3%) were carriers, with eight of 12 (66.7%) from the same dormitory. All staff members screened negative. After intensified control measures, the number of students screened positive for CA-MRSA decreased from nine to one with no more cases identified in the school.Conclusion：Identification of carriers, decolonization therapy, monitoring of cases and contacts and strengthening of environmental and personal hygiene were control measures that helped contain this CA-MRSA outbreak in a boarding school in Hong Kong Special Administrative Region (China).