Benjamin J Cowling

The University of Hong Kong | HKU · School of Public Health

Background Annual influenza vaccination is recommended for older adults but repeated vaccination with standard-dose influenza vaccine has been linked to reduced immunogenicity and effectiveness, especially against A(H3N2) viruses. Methods Community-dwelling Hong Kong adults aged 65-82 years were randomly allocated to receive 2017/18 standard-dose...

To date there is a lack of randomized trial data examining the use of the antiviral nirmatrelvir/ritonavir in SARS-CoV-2-infected pregnant persons. This target trial emulation study aims to address this gap by evaluating the use of nirmatrelvir/ritonavir in non-hospitalized pregnant women with symptomatic SARS-CoV-2 Omicron variant infection. Among...

Soon after a mask mandate was relaxed (March 1, 2023), the first post-COVID-19 influenza season in Hong Kong lasted 12 weeks. After other preventive measures were accounted for, mask wearing was associated with an estimated 25% reduction in influenza transmission. Influenza resurgence probably resulted from relaxation of mask mandates and other mea...

Importance Hong Kong was held as an exemplar for pandemic response until it recorded the world’s highest daily COVID-19 mortality, which was likely due to vaccine refusal. To prevent this high mortality in future pandemics, information on underlying reasons for vaccine refusal is necessary. Objectives To track the evolution of COVID-19 vaccination...

In March-June 2023 we conducted a test negative study in 1671 children who were hospitalized with acute respiratory illness in Hong Kong. 286 (17.2%) tested positive for influenza virus including 188 with A(H1N1). We estimated influenza vaccine effectiveness against influenza-associated hospitalization as 69.6% (95% confidence interval: 49.3%, 81.7...

The time-varying effective reproduction number (Rt at time t) measures the transmissibility of SARS-CoV-2 and is conventionally based on daily case counts which may suffer from time-varying ascertainment. We analyzed Rt estimates from case counts, and severe COVID-19 (ICU admissions, severe or critical cases, and mortality) across 2022 in Hong Kong...

We introduce the angular reproduction number Ω, which measures time-varying changes in epidemic transmissibility resulting from variations in both the effective reproduction number R, and generation time distribution w. Predominant approaches for tracking pathogen spread infer either R or the epidemic growth rate r. However, R is biased by mismatch...

Promoting high vaccine uptake is a primary public health policy in mitigating the profound impact of COVID-19 pandemic. The evolution of the COVID-19 pandemic requires a dynamic evaluation of factors that are associated with COVID-19 vaccination uptake to inform a strategic plan on vaccination programmes. Using real-time population-based data that...

Background: Assessment of viral kinetics of SARS-CoV-2 can inform on host immune responses to the virus and on the viral transmission potential. We aimed to characterise viral shedding kinetics by age, virus type, and clinical outcome, and to examine the potential effect of vaccination on viral shedding. Methods: In this retrospective observatio...

In this cohort study conducted in Hong Kong where both bivalent and monovalent formulations of BNT162b2 were available, there was no significant differences in the mortality or hospitalization between those who received bivalent and monovalent mRNA as second boosters. Bivalent and monovalent mRNA boosters appear equally protective against clinical...

As the pandemic's dynamics changed, many municipalities lifted face wearing requirement in school which was initially implemented to mitigate the transmission of COVID-19. This study examines the effects of lifting mask mandates on COVID-19 transmission within Massachusetts school districts. We first replicated previous research by Cowger et al. (2...

Social distancing measures (SDMs) are community-level interventions that aim to reduce person-to-person contacts in the community. SDMs were a major part of the responses first to contain, then to mitigate, the spread of SARS-CoV-2 in the community. Common SDMs included limiting the size of gatherings, closing schools and/or workplaces, implementin...

We administered BNT162b2 as a third dose to 314 adults ≥30 years of age who had previously received 2 doses of inactivated vaccine. We collected blood samples before the third dose and again after 1, 6 and 12 months, and found stable levels of antibody responses to the ancestral strain and Omicron BA.2 at 6-12 months after receipt of the BNT162b2 t...

Test negative studies have been used extensively for the estimation of COVID-19 vaccine effectiveness (VE). Such studies are able to estimate VE against medically-attended illness under certain assumptions. Selection bias may be present if the probability of participation is associated with vaccination or COVID-19, but this can be mitigated through...

China announced a slight easing of its zero-COVID rules on November 11, 2022, and then a major relaxation on December 7, 2022. We estimate that the ensuing wave of SARS-CoV-2 infections caused 1.41 million deaths in China during December 2022-February 2023, substantially higher than that reported through official channels.

There has long been controversy over the potential for asymptomatic cases of the influenza virus to have the capacity for onward transmission, but recognition of asymptomatic transmission of COVID-19 stimulates further research into this topic. Here, we develop a Bayesian methodology to analyze detailed data from a large cohort of 727 households an...

As influenza A virus (IAV) infection establishes a more diverse immunological memory to different viral proteins compared to vaccination, we hypothesize that this could skew antibody responses to immunizing antigens after infection. To explore this, we generated mouse models that possess either an IAV hemagglutinin (HA)- or neuraminidase (NA)-biase...

Background: Few trials have compared homologous and heterologous third doses of COVID-19 vaccination with inactivated vaccines and mRNA vaccines. The aim of this study was to assess immune responses, safety, and efficacy against SARS-CoV-2 infection following homologous or heterologous third-dose COVID-19 vaccination with either one dose of Corona...

Background: High COVID-19 vaccination uptake rates across all age groups are important for achieving herd immunity. However, age disparity in vaccination acceptance was consistently identified. Objective: Taking cues from tenets of socioemotional selectivity theory, this study examined how the contextual and psychosocial factors contributed to a...

We show that school closures reduced COVID-19 incidence rates in children by 31%-46% in Hong Kong in 2022. After school reopening accompanied by mask mandates, daily rapid testing, and vaccination requirements, school-reported cases correlated with community incidence rates. Safe school reopening is possible when appropriate preventive measures are...

COVID-19 measures influenced respiratory virus epidemiology in Hong Kong. Rhinoviruses/enteroviruses became dominant as measures eased, with HRV genotypes A and C persisting in children. A resurgence of HRV A cases occurred during relaxation of measures, while strict measures reduced virus circulation but increased overall diversity. HRV genotypes...

Background: Elevations in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were reported as adverse events of nirmatrelvir/ritonavir users in the EPIC-HR trial. Aim: To quantify the risk and severity of acute liver injury (ALI) associated with nirmatrelvir/ritonavir use. Methods: This self-controlled case-series study was co...

Background: Understanding severity of infections with SARS-CoV-2 and its variants is crucial to inform public health measures. Here we used COVID-19 patient data from Hong Kong to characterise the severity profile of COVID-19. Methods: Time-varying and age-specific effective severity measured by case-hospitalization risk and hospitalization-fata...

Background: Hong Kong contained COVID-19 for two years, but experienced a large epidemic of Omicron BA.2 in early 2022 and endemic transmission of Omicron subvariants thereafter. Methods: We examined the use and impact of pandemic controls in Hong Kong by analysing data on more than 1.7 million confirmed COVID-19 cases and characterizing non-pharma...

Background: Hong Kong experienced four epidemic waves caused by the ancestral strain of SARS-CoV-2 in 2020-2021 and a large Omicron wave in 2022. Few studies have assessed antibacterial drug prescribing for COVID-19 inpatients throughout the pandemic. Objectives: To describe inpatient antibacterial drug prescribing for COVID-19 patients throughout...

The antiviral drug Paxlovid has been shown to rapidly reduce viral load. Coupled with vaccination, timely administration of safe and effective antivirals could provide a path towards managing COVID-19 without restrictive non-pharmaceutical measures. Here, we estimate the population-level impacts of expanding treatment with Paxlovid in the US using...

To support the ongoing management of viral respiratory diseases, many countries are moving towards an integrated model of surveillance for SARS-CoV-2, influenza, and other respiratory pathogens. While many surveillance approaches catalysed by the COVID-19 pandemic provide novel epidemiological insight, continuing them as implemented during the pand...

Background: Understanding factors associated with SARS-CoV-2 exposure risk in the hospital setting may help improve infection control measures for prevention. Aim: To monitor SARS-CoV-2 exposure risk among healthcare workers and to identify risk factors associated with SARS-CoV-2 detection. Methods: Surface and air samples were collected longi...

Background: People with substance use disorder have a high risk of SARS-CoV-2 infection and subsequent poor outcomes. Few studies have evaluated COVID-19 vaccine effectiveness among people with substance use disorder. We aimed to estimate the vaccine effectiveness of BNT162b2 (Fosun-BioNTech) and CoronaVac (Sinovac) against SARS-CoV-2 omicron (B.1...

Importance: Diabetes and COVID-19 are both global pandemics, and type 2 diabetes is a common comorbidity in patients with acute COVID-19 and is proven to be a key determinant of COVID-19 prognosis. Molnupiravir and nirmatrelvir-ritonavir are oral antiviral medications recently approved for nonhospitalized patients with mild to moderate COVID-19, f...

Hong Kong experienced a surge of Omicron BA.2 infections in early 2022, resulting in one of the highest per-capita death rates of COVID-19. The outbreak occurred in a dense population with low immunity towards natural SARS-CoV-2 infection, high vaccine hesitancy in vulnerable populations, comprehensive disease surveillance and the capacity for stri...

We described the frequency of residential case clusters and the efficiency of compulsory testing in identifying cases using buildings targeted in compulsory testing and locally infected COVID-19 cases matched by residence in Hong Kong. Most of the buildings (4246/7688, 55.2%) with COVID-19 cases identified had only one reported case and 13% of the...

Background: School-located influenza vaccination programme (SIVP) can effectively promote childhood seasonal influenza vaccination (SIV). However, the longitudinal effects of continuation and discontinuation of the SIVP on parents' vaccine hesitancy remained unknown. Methods: A two-wave longitudinal study recruited adult parents who had at least...

Test negative studies have been used extensively for the estimation of COVID-19 vaccine effectiveness (VE). Such studies are able to estimate VE against medically-attended illness under certain assumptions. Selection bias may be present if the probability of participation is associated with vaccination or COVID-19, but this can be mitigated through...

Purpose of review: Initial response strategies to the COVID-19 pandemic were heavily reliant on nonpharmaceutical interventions (NPIs), a set of measures implemented to slow or even stop the spread of infection. Here, we reviewed key measures used during the COVID-19 pandemic. Recent findings: Some NPIs were successful in reducing the transmissi...

The two nearby Amazonian cities of Iquitos and Manaus endured explosive COVID-19 epidemics and may well have suffered the world's highest infection and death rates over 2020, the first year of the pandemic. State-of-the-art epidemiological and modeling studies estimated that the populations of both cities came close to attaining herd immunity (>70%...

Background: Understanding severity of infections with SARS-CoV-2 and its variants is crucial to inform public health measures. Here we used COVID-19 patient data from Hong Kong to characterise the severity profile of COVID-19 and to examine factors associated with fatality of infection. Methods: Time-varying and age-specific effective severity meas...

Background: Coronavirus disease 2019 (COVID-19) continues to be a major global public health crisis that exacts significant human and economic costs. Booster vaccination of individuals can improve waning immunity and reduce the impact of community epidemics. Methods: Using an epidemiological model that incorporates population-level severe acute...

The COVID-19 pandemic has highlighted important considerations for modeling future pandemics.

Background: Viral rebound after nirmatrelvir-ritonavir treatment has implications for the clinical management and isolation of patients with COVID-19. We evaluated an unselected, population-wide cohort to identify the incidence of viral burden rebound and associated risk factors and clinical outcomes. Methods: We did a retrospective cohort study...

In randomized controlled trials of influenza vaccination, 550 children received trivalent-inactivated influenza vaccine, permitting us to explore relationship between vaccine response and host single nucleotide polymorphisms (SNPs) in 23 candidate genes with adjustment of multiple testing. For host SNPs in TLR7–1817G/T (rs5741880), genotype GT was...

What is already known about this topic? People are likely to engage in collective behaviors online during extreme events, such as the coronavirus disease 2019 (COVID-19) crisis, to express awareness, take action, and work through concerns. What is added by this report? This study offers a framework for evaluating interactions among individuals’ em...

A SARS-CoV-2 Omicron BA.5 outbreak occurred in Macau from mid-June through July 2022. Out of >1,800 laboratory-confirmed cases, most were mild or asymptomatic; only 6 deaths were recorded. The outbreak was controlled through stringent public health and social measures, such as repeated universal testing and a stay-at-home order lasting 2 weeks.

Influenza imprinting reduces risks of influenza A virus clinical infection by 40-90% estimated from surveillance data in western countries. We analyzed surveillance data from 2010-2019 in Hong Kong. Based on the best model included HA group-level imprinting, we estimated that individuals imprinted to H1N1 or H2N2 had a 17% (95% CI: 3%, 28%) lower r...

Background: Influenza causes considerable disease burden each year, particularly in children. Monitoring school absenteeism has long been proposed as a surveillance tool of influenza activity in the community, but the practice of school absenteeism could be varying, and the potential of such usage remains unclear. Objective: The aim of this pape...

Background On-arrival quarantine has been one of the primary measures to prevent the introduction of SARS-CoV-2 into Hong Kong since the start of the pandemic. Most on-arrival quarantines have been done in hotels, with the duration of quarantine and testing frequency during quarantine modified over time along with other pandemic control measures. H...

Background Hong Kong followed a strict COVID-19 elimination strategy in 2020. We estimated the impact of the COVID-19 pandemic responses on all-cause and cause-specific hospitalizations and deaths in 2020. Methods Interrupted time-series analysis using negative binomial regression accounting for seasonality and long-term trend was used on weekly 2...

Background Accurate estimation of household secondary attack rate (SAR) is crucial to understand the transmissibility of SARS-CoV-2. The impact of population-level factors, such as transmission intensity in the community on SAR estimates are however rarely explored. Methods In this study, we included articles with original data to compute the hous...

The generation time distribution, reflecting the time between successive infections in transmission chains, is a key epidemiological parameter for describing COVID-19 transmission dynamics. However, because exact infection times are rarely known, it is often approximated by the serial interval distribution. This approximation holds under the assump...

Background: The time-varying reproduction number, Rt, is commonly used to monitor the transmissibility of an infectious disease during an epidemic, but standard methods for estimating Rt seldom account for the impact of overdispersion on transmission. Methods: We developed a negative binomial framework to estimate Rt and a time-varying dispersio...

People are likely to engage in collective behaviour online during extreme events, such as the COVID-19 crisis, to express their awareness, actions and concerns. Hong Kong has implemented stringent public health and social measures (PHSMs) to curb COVID-19 epidemic waves since the first COVID-19 case was confirmed on 22 January 2020. People are like...

Background: COVID-19 vaccines provide protection against symptomatic infection that might require medical attention and against severe outcomes; however, there is a paucity of evidence regarding the effectiveness of the BNT162b2 and CoronaVac vaccines and their booster regimens against asymptomatic or mild omicron infections in the community. We a...

Enterovirus A71 (EV-A71)–related hand, foot, and mouth disease (HFMD) imposes a substantial clinical burden in the Asia Pacific region. To inform policy on the introduction of the EV-A71 vaccine into the National Immunization Programme, we investigated the seroepidemiological characteristics of EV-A71 in two prospective cohorts of children in south...

With the emergence of SARS-CoV-2 variants that eluded immunity from vaccines and prior infections, vaccine shortages and their effectiveness pose unprecedented challenges for governments to expand booster vaccination programs. Fractionation of vaccine doses might be an effective strategy to help society to face these challenges, which may have comp...

Hong Kong has implemented stringent public health and social measures (PHSMs) to curb each of the four COVID-19 epidemic waves since January 2020. The third wave between July and September 2020 was brought under control within 2 m, while the fourth wave starting from the end of October 2020 has taken longer to bring under control and lasted at leas...

Introduction: The ease of coronavirus disease 2019 (COVID-19) non-pharmacological interventions and the increased susceptibility during the past COVID-19 pandemic could be a precursor for the resurgence of influenza, potentially leading to a severe outbreak in the winter of 2022 and future seasons. The recent increased availability of data on Elec...

Assessment of viral kinetics of SARS-CoV-2 may inform host immune responses to and transmission potential of the virus. We analyzed longitudinal data of RT-PCR tests conducted for symptomatic COVID-19 patients at confirmation and during hospital isolation in Hong Kong during three major epidemic waves, and modeled the temporal trajectories of viral...

Annual seasonal influenza vaccination is recommended for individuals at high risk of developing post-infection complications in many locations. However, reduced vaccine immunogenicity and effectiveness have been observed among repeat vaccinees in some influenza seasons. We investigated the impact of repeated influenza vaccination on relative vaccin...

Background Dose fractionation of a coronavirus disease 2019 (COVID-19) vaccine could effectively accelerate global vaccine coverage, while supporting evidence of efficacy, immunogenicity, and safety are unavailable, especially with emerging variants. Methods We systematically reviewed clinical trials that reported dose-finding results and estimate...

Vaccines that are broadly cross-protective against current and future SARS-CoV-2 variants of concern (VoC) or across the sarbecoviruses subgenus remain a priority for public health. Virus neutralization is the best available correlate of protection. To define the magnitude and breadth of cross-neutralization in individuals with different exposure t...

Background The transmission dynamics of influenza were affected by public health and social measures (PHSMs) implemented globally since early 2020 to mitigate the COVID-19 pandemic. We aimed to assess the effect of COVID-19 PHSMs on the transmissibility of influenza viruses and to predict upcoming influenza epidemics. Methods For this modelling st...

Background Despite relatively few reports of residential case clusters of COVID-19, building-wide compulsory testing notices on residential apartment blocks are frequently applied in Hong Kong with the aim of identifying cases and reducing transmission. Methods We aimed to describe the frequency of residential case clusters and the efficiency of c...

Introduction Minimizing the importation and exportation risks of coronavirus disease 2019 (COVID-19) is a primary concern for sustaining the “Dynamic COVID-zero” strategy in China. Risk estimation is essential for cities to conduct before relaxing border control measures. Methods Informed by the daily number of passengers traveling between 367 pre...

Background The world is undergoing an unprecedented wave of urbanization. However, the effect of rapid urbanization during the early or middle stages of urbanization on seasonal influenza transmission remains unknown. Since about 70% of the world population live in low-income countries, exploring the impact of urbanization on influenza transmission...

BACKGROUND The world is undergoing an unprecedented wave of urbanization. However, the effect of rapid urbanization during the early or middle stages of urbanization on seasonal influenza transmission remains unknown. Since about 70% of the world population live in low-income countries, exploring the impact of urbanization on influenza transmission...

Background Little is known about the real-world effectiveness of oral antivirals against the SARS-CoV-2 omicron (B.1.1.529) variant. We aimed to assess the clinical effectiveness of two oral antiviral drugs among community-dwelling COVID-19 outpatients in Hong Kong. Methods In this observational study, we used data from the Hong Kong Hospital Auth...

Objectives : We aimed to explore the transmission dynamics of the Omicron BA.1.1 variant in an outbreak in China. Methods : We constructed 113 transmission pairs based on the time of exposure and symptom onset for identified infectors and infectees, using the epidemiological data collected during an outbreak in Hangzhou, Zhejiang province, China,...

After keeping infections at bay for two years, Hong Kong experienced a surge of Omicron BA.2 infections in early 2022 that overwhelmed the health care system, isolation facilities, and contact tracing capacity, leading to one of the highest per-capita death rates of COVID-19 in early 2022. The outbreak occurred against a backdrop of a dense populat...

We analysed the effectiveness of various non-pharmaceutical interventions in containing the 2022 Omicron outbreak in China. The results show that the Rapid Antigen Test contributed to containing the outbreak, reducing the reproduction number by 0.788 (95% CI:-0.306, 1.880) in studied cities.

Influenza vaccination is an important intervention to prevent influenza virus infection. Our previous analysis suggested that indirect protection is limited in an influenza B epidemic in Hong Kong. We further analyzed six influenza A epidemics to determine such potential. We applied a statistical model to estimate household transmission dynamics in...

The performance of gargling for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reverse transcriptase (RT)-PCR testing has not been previously reviewed. This review systematically assessed the performance of saline and water gargling for SARS-CoV-2 RT-PCR testing in the settings of diagnosing and monitoring viral shedding. We included...

We administered BNT162b2 as a third dose to 314 adults aged ≥30 years who had previously received two doses of inactivated vaccination. We collected blood samples before the third dose and again after one month and six months, and found r