Susan Shui Seng Chiu

Effects of Nonpharmaceutical Interventions

We diagnosed varicella zoster virus (VZV) meningitis in a healthy adolescent boy who presented without a rash or fever. We aim to compare VZV reactivation meningitis in children after primary VZV infection and VZV vaccination. We reviewed the literature up until June 2020 using Pubmed/MEDLINE and EMBASE databases using ‘varicella zoster’, ‘meningitis’ and ‘children’ as keywords. Only English articles were included. Twenty‐five cases were included in this review. Children who had VZV reactivation meningitis after vaccination were younger (7 ± 3.4 years vs. 11.9 ± 3.6 years, P = 0.0038), had a shorter interval between first exposure to reactivation (5.6 ± 2.9 years vs. 8.8 ± 3.2 years, P = 0.018) and more likely to have a rash (100% vs. 55%, P = 0.04). VZV reactivation meningitis occurs after both primary VZV infection and VZV vaccination. The absence of exanthem, fever or meningism does not rule out VZV meningitis.

Background: A range of public health measures have been implemented to delay and reduce local transmission of COVID-19 in Hong Kong, and there have been major changes in behaviours of the general public. We examined the effect of these interventions and behavioral changes on the incidence of COVID-19 as well as on influenza virus infections which may share some aspects of transmission dynamics with COVID-19. Methods: We reviewed policy interventions and measured changes in population behaviours through two telephone surveys, on January 20-23 and February 11-14. 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 ( R _t ), for COVID-19 and influenza A(H1N1). Findings: COVID-19 transmissibility has remained at or below 1, indicating successful containment to date. Influenza transmission declined substantially after the implementation of social distancing measures and changes in population behaviours in late January, with a 44% (95% confidence interval, CI: 34% to 53%) reduction in transmissibility in the community, and a 33% (95% CI: 24% to 43%) reduction in transmissibility based on paediatric hospitalization rates. In the two surveys we estimated that 74.5% and 97.5% of the general adult population wore masks when going out, and 61.3% and 90.2% avoided going to crowded places, respectively. Implications: Containment measures, social distancing measures and changes in population behaviour have successfully prevented spread of COVID-19. The social distancing measures and behavioural changes led to a substantial reduction in influenza transmission in early February 2020. However, it may be challenging to avoid fatigue and sustain these measures and population behaviours as COVID-19 continues to spread globally. Funding: Health and Medical Research Fund, Hong Kong

Background: Two doses of influenza vaccination are recommended for previously unvaccinated children aged <9 years, and receipt of 1 dose is sometimes termed “partial vaccination.” We assessed the effectiveness of partial and full influenza vaccination in preventing influenza-associated hospitalization among children in Hong Kong. Methods: Using the test-negative design we enrolled 23 187 children aged <9 years admitted to hospitals with acute respiratory illness from September 2011 through March 2019. Vaccination and influenza status were recorded. Fully vaccinated children included those vaccinated with 2 doses or, if previously vaccinated, those vaccinated with 1 dose. Partially vaccinated children included those who should have received 2 doses but only received 1 dose. We estimated vaccine effectiveness (VE) by using conditional logistic regression models matched on epidemiological week. Results: Overall VE estimates among fully and partially vaccinated children were 73% (95% confidence interval, 69%–77%) and 31% (95% confidence interval, 8%–48%), respectively. A consistently higher VE was observed in children fully vaccinated against each influenza virus type/subtype. The effectiveness of partial vaccination did not vary by age group. Conclusions: Partial vaccination was significantly less effective than full vaccination. Our study supports the current recommendation of 2 doses of influenza vaccination in previously unvaccinated children <9 years of age.

Influenza and pneumococcal vaccine uptake in the older population aged 65 years or over of Hong Kong dramatically increased since the 2003 SARS outbreak. This study is aimed to evaluate the impact of increased coverage of influenza and pneumococcal vaccines by comparing the change of disease burden in the older population of Hong Kong, with the burden in the older population of Brisbane with relatively high vaccine coverage in the past fifteen years. Time series segmented regression models were applied to weekly numbers of cause-specific mortality or hospitalization of Hong Kong and Brisbane. Annual excess rates of mortality or hospitalization associated with influenza in the older population were estimated for the pre-SARS (reference period), post-SARS and post-pandemic period, respectively. The rate ratios (RRs) between these periods were also calculated to assess the relative change of disease burden. Compared to the pre-SARS period, excess rates of mortality associated with influenza during the post-SARS period in Hong Kong decreased for cardiorespiratory diseases (RR = 0.90, 95% CI 0.80, 1.01), stroke (RR = 0.74, 95% CI 0.50, 1.09), and ischemic heart diseases (RR = 0.45, 95% CI 0.34, 0.58). The corresponding RRs in Brisbane were 0.79 (95% CI 0.54, 1.15), 0.33 (0.13, 0.80), and 1.09 (0.62, 1.90), respectively. Only the mortality of ischemic heart diseases showed a greater reduction in Hong Kong than in Brisbane. During the post-pandemic period, excess rates of all-cause mortality increased in Hong Kong, but to a lesser extent than in Brisbane (RR = 1.41 vs 2.39). A relative decrease (or less of an increase) of influenza disease burden was observed in the older population of Hong Kong after increased coverage of influenza and pneumococcal vaccines in this population, as compared to those of Brisbane where vaccination rates remained stable. The lack of significant findings in some disease categories highlights the challenges of evaluating the benefits of vaccination at the population level.

The winter 2018/19 influenza season in Hong Kong has been predominated by influenza A(H1N1)pdm09 as at January 2019. We enrolled 2,016 children in three public hospitals in Hong Kong between 2 September 2018 and 11 January 2019. Using the test-negative approach, we estimated high early season effectiveness of inactivated influenza vaccine against influenza A or B of 90% (95% confidence interval (CI): 80–95%) and 92% (95% CI: 82–96%) against influenza A(H1N1)pdm09.

This study used several datasets of reported and serotyped invasive pneumococcal disease (IPD) cases to estimate vaccine and non-vaccine type incidence in Hong Kong children. Incidence was analyzed by four time periods to indicate pre-PCV (period 1, 1995–2004), private market only (period 2, 2006–2009), and following early (period 3, 2010–2014, mixed use of 7-, 10- and 13-valent vaccines) and more than five years (period 4, 2015–2017, 13-valent vaccine only) of routine implementation (since September 2009). IPD incidence decreased by 85% and 35% in aged < 2 years and aged 2 to < 5 years, respectively, from period 1 to period 4. This was due to a 97% reduction in the serotypes covered by 7-valent vaccine. In period 4, 59% of the disease was caused by serotype 3 and was largely attributed to an ermB positive, novel ST6011 clone. The finding corroborates an increasing body of evidence that the efficacy of the 13-valent vaccine against infection by this serotype is low.

We conducted a hospital-based test-negative study in Hong Kong to estimate influenza vaccine effectiveness (VE) for the winter of 2017/18. The interim analysis included data on 1,078 children admitted between 4 December 2017 and 31 January 2018 with febrile acute respiratory illness and tested for influenza. We estimated influenza VE at 66% (95% confidence interval (CI): 43–79) overall, and 65% (95% CI: 40–80) against influenza B, the dominant virus type (predominantly B/Yamagata).