We assessed the association between voluntary polymerase chain reaction testing of travellers and reported infection rates in the Ogasawara Islands compared with those in several other Tokyo islands. The implementation of polymerase chain reaction testing over a 2-year period was evaluated. Between September 2020 and September 2022, 38,943 of 45,900 travellers to the Ogasawara Islands underwent pre-travel polymerase chain reaction testing, with a notable increase in uptake during states of emergency. Ogasawara reported 385 positive coronavirus disease 2019 cases, with no hospitalizations or severe cases among residents, in contrast to the higher infection and hospitalization rates in Tokyo. Pre-boarding polymerase chain reaction tests were associated with lower reported infection rates in this island setting. These findings suggest that combining pre-travel testing with local mitigation measures, including case isolation systems, may help safeguard the communities of small, geographically isolated islands. These results may inform public health preparedness and response strategies for future infectious disease outbreaks.

To estimate illness incidence or prevalence from wastewater data, modelling approaches may benefit from incorporating faecal shedding parameters. We systematically searched PubMed and a public repository on shedding data and included 33 studies that met at least one of our objectives. Among 32 studies, the proportion of SARS-CoV-2-infected individuals with detectable virus in stool ranged from 18 to 100%, with a pooled estimate of 54% (95% CI: 52–56%). Stratification by four clinical severity categories, ranging from asymptomatic to critically ill, showed no significant differences among categories (p-value = 0.49). The proportion of individuals with detectable SARS-CoV-2 RNA in stool was higher in children (61%) than in adults (53%; p-value = 0.02). In half of the individuals who initially shed the virus in stool, it remained detectable for an estimated 22 days post-symptom onset. Three studies documented viral load kinetics, indicating a peak between days 3 and 9. Twenty-five studies reported maximum shedding durations ranging from 2 to 12 weeks. Our review summarizes the frequency, dynamics, and duration of SARS-CoV-2 shedding in stool and may serve as a valuable foundation for modelling efforts involving faecal shedding indicators.

After the Zero COVID policy ended on December 7, 2022, ~90% of mainland Chinese were infected in a COVID-19 wave. This systematic review synthesized research estimating excess mortality during that wave in mainland China. We searched seven databases in May 2024 and updated our search in July–August 2025. Peer-reviewed research (Chinese or English), published since January 1, 2023, estimating excess deaths in the COVID-19 wave post-Zero-COVID was included. Risk of bias was assessed using a modified Newcastle-Ottawa Scale. Two authors independently conducted abstract screening, full-text review, data extraction, and risk-of-bias assessment. Seven articles were included. Two studies analysed the death records of a town and a district in Shanghai, estimating the excess mortality rates of 153.6% and 174.3%, respectively. Using indirect methods, four studies estimated national excess mortality (range: 0.71–1.87 million). Another study estimated excess mortality in Taiyuan. Studies used diverse methods to estimate excess deaths, resulting in widely varying and uncertain estimates. Choice of reference period, seasonality, and other factors affect expected mortality estimates.

The activity of respiratory viruses (RVs) displays large variability in tropical regions, posing challenges for public health response strategies. Data from most RVs in south-eastern Mexico remain limited, particularly in the Yucatan Peninsula, the largest tourism hub in the country. This retrospective study analyses the regional epidemiology of RVs in Merida, the largest city in the region, using laboratory test data from a local hospital (January 2018–April 2024). Test results of 143292 RVs were collected, including 121976 for SARS-CoV-2, 19355 for influenza A and B viruses, and 1961 for 17 distinct RVs. We found that non-SARS-CoV-2 RVs circulated year-round, with higher activity in autumn and spring, while SARS-CoV-2 peaked in summer and winter. Influenza A virus, respiratory syncytial virus, and influenza B virus reached their highest activity in autumn, earlier than in other regions of Mexico. Human metapneumovirus peaked during autumn-winter. Rhinovirus/enterovirus and parainfluenza showed year-round activity, with peaks in autumn and spring. Other coronaviruses were more frequent during winter-spring. In post-pandemic years (2022–2023), adenovirus outbreaks emerged, as well as an increased prevalence of non-SARS-CoV-2 RV co-infections. This study highlights the need for region-specific public health strategies, including optimized vaccination schedules, such as for influenza A virus, and enhanced diagnostic surveillance.

We estimated the vaccine effectiveness (VE) of second monovalent and bivalent booster vaccines containing Omicron BA.1 or BA.4/BA.5 and the protection conferred by natural immunity against SARS-CoV-2 infection in Luxembourg. We conducted a test-negative case–control study among residents aged 60 years or older by integrating national socio-demographic, COVID-19 vaccination, and testing data, achieving full population coverage. Using conditional logistic regression, we estimated absolute and relative VE of monovalent and bivalent boosters and natural immunity from prior infection. Our analysis included 5,390 test-positive cases and 11,048 test-negative controls matched by week of testing between September 2022 and April 2023. Absolute VE for monovalent and bivalent boosters decreased from 64.8% and 66.6% in the first month to 1.5% and 16.5% after 5–6 months, respectively. The bivalent was superior to the monovalent booster only in individuals without natural immunity (relative VE 25.7%, 95% confidence interval 11.4%; 37.7%). Natural immunity lasted longer than vaccine-induced immunity with 80.7% protected at 4–8 months and 44.9% at 15–25 months post-infection. Both second booster vaccines provided temporary protection against SARS-CoV-2 infection; bivalent boosters offered a slight benefit over monovalent boosters. Natural immunity appears to confer longer-lasting protection.

Early in the COVID-19 pandemic, Denmark launched COVIDmeter, a national participatory surveillance platform collecting real-time, self-reported symptoms from a community cohort, aimed to support early signal detection of COVID-like illness. This study describes the community cohort, the reported symptoms among persons testing positive and evaluates COVIDmeter’s performance in detecting trends compared to other established surveillance indicators. A total of 143000 individuals registered as participants, of whom 98% completed at least one weekly questionnaire, resulting in approximately 5.8 million responses over the period from March 2020 to March 2023. Of those who tested positive, the most commonly reported symptoms overall were headache, fatigue, muscle or body aches, cough and fever. Trends in COVID-like illness followed similar patterns to other indicators, with COVID-like illness peaks often preceding increases in incidence and hospital admissions, suggesting early detection potential. The study demonstrated that participatory surveillance can serve as an early detection tool for tracking infection trends, particularly in the early stages of a pandemic. While subject to limitations such as selection bias and self-reporting inaccuracies and participatory symptom surveillance proved to be a rapid, scalable and cost-effective complement to traditional surveillance independent of virus testing, this highlights its relevance for future pandemic preparedness.

The objective of this study was to evaluate the impact on SARS-CoV-2 transmission prevention of mask wearing by index cases and their household contacts. A prospective study of SARS-CoV-2 transmission to household contacts aged ≥18 years was conducted between May 2022 and February 2024 in Spain. Contacts underwent a rapid antigen test on day zero and a real-time polymerase chain reaction test 7 days later if results were negative. The dependent variable was SARS-CoV-2 infection in contacts. Index case and contact mask use effects were estimated using the adjusted odds ratio (aOR) and its 95% confidence interval (CI). Studied were 230 household contacts, mean (standard deviation) age 53.3 (16.6) years, and 47.8% (110/230) women. Following index case diagnosis, 36.1% of contacts (83/230) used a mask, and 54.3% (125/230) were exposed to a mask-wearing index case. Infection incidence in contacts was 45.2% (104/230) and was lower in contacts exposed to mask-wearing index cases (36.0% vs. 56.2%; p < 0.002). The logistic regression model indicated a protective effect for contacts of both index case mask use (aOR = 0.31; 95% CI: 0.15–0.65) and vaccination (aOR = 0.24; 95% CI: 0.08–0.77). Index case mask use reduced SARS-CoV-2 transmission to contacts, while mask effectiveness was not observed for contacts.

Determining the factors that impact the risk for infection with SARS-CoV-2 is a priority as the virus continues to infect people worldwide. The objective was to determine the effectiveness of vaccines and other factors associated with infection among Canadian healthcare workers (HCWs) followed from 15 June 2020 to 1 December 2023. We also investigate the association between antibodies to SARS-CoV-2 and subsequent infections with SARS-CoV-2. Of the 2474 eligible participants, 2133 (86%) were female, 33% were nurses, the median age was 41 years, and 99.3% had received at least two doses of COVID-19 vaccine by 31 December 2021. The incidence of SARS-CoV-2 was 0.91 per 1000 person-days. Prior to the circulation of the Omicron variants, vaccine effectiveness (VE) was estimated at 85% (95% CI 1, 98) for participants who received the primary series of vaccine. During the Omicron period, relative adjusted VE was 43% (95% CI 29, 54), 56% (95% CI 42, 67), and 46% (95% CI 24, 62) for 3, 4, and ≥ 5 doses compared with those who received primary series after adjusting for previous infection and other covariates. Exposure to infected household members, coworkers, or friends in the previous 14 days were risk factor for infection, while contact with an infected patient was not statistically significant. Participants with higher levels of immunoglobulin G (IgG) anti-receptor binding domain (RBD) antibodies had lower rates of infection than those with the lowest levels. COVID-19 vaccines remained effective throughout the follow-up of this cohort of highly vaccinated HCWs. IgG anti-RBD antibody levels may be useful as correlates of protection for issues such as vaccine development and testing. There remains a need to increase the awareness among HCWs about the risk of contracting SARS-CoV-2 from contacts at a variety of venues.

Health-related quality of life (HRQoL) in the context of COVID-19 is not fully understood. We assessed HRQoL using Patient-Reported Outcomes Measurement Information System® measures among 559 former COVID-19 patients and 298 non-infected individuals. HRQoL was captured once up to 2 years after the initial test. Additionally, we described associations of characteristics with impaired HRQoL. Overall, HRQoL scores were inferior among former patients. A meaningful group difference of at least three T-score points was discernible until 12 months after testing for fatigue (3.1), sleep disturbance (3.5), and dyspnoea (3.7). Cognitive function demonstrated such difference even at >18 months post-infection (3.3). Following dichotomization, pronounced differences in impaired HRQoL were observed in physical (19.2% of former patients, 7.3% of non-infected) and cognitive function (37.6% of former patients, 16.5% of non-infected). Domains most commonly affected among former patients were depression (34.9%), fatigue (37.4%), and cognitive function. Factors that associated with HRQoL impairments among former patients included age (OR ≤2.1), lower education (OR ≤5.3), and COVID-19-related hospitalization (OR ≤4.7), among others. These data underline the need for continued attention of the scientific community to further investigate potential long-term health limitations after COVID-19 to ultimately establish adequate screening and management options for those affected.

Within an infrastructure to monitor vaccine effectiveness (VE) against hospitalization due to COVID-19 and COVID-19 related deaths from November 2022 to July 2023 in seven countries in real-world conditions (VEBIS network), we compared two approaches: (a) estimating VE of the first, second or third COVID-19 booster doses administered during the autumn of 2022, and (b) estimating VE of the autumn vaccination dose regardless of the number of prior doses (autumnal booster approach). Retrospective cohorts were constructed using Electronic Health Records at each participating site. Cox regressions with time-changing vaccination status were fit and site-specific estimates were combined using random-effects meta-analysis. VE estimates with both approaches were mostly similar, particularly shortly after the start of the vaccination campaign, and showed a similar timing of VE waning. However, autumnal booster estimates were more precise and showed a clearer trend, particularly compared to third booster estimates, as calendar time increased after the vaccination campaign and during periods of lower SARS-CoV-2 activity. Moreover, the decrease in protection by increasing calendar time was more clear and precise than when comparing protection by number of doses. Therefore, estimating VE under an autumnal booster framework emerges as a preferred method for future monitoring of COVID-19 vaccination campaigns.

Denmark is one of the leading countries in establishing digital solutions in the health sector. When SARS-CoV-2 arrived in February 2020, a real-time surveillance system could be rapidly built on existing infrastructure. This rapid data integration for COVID-19 surveillance enabled a data-driven response. Here we describe (a) the setup of the automated, real-time surveillance and vaccination monitoring system for COVID-19 in Denmark, including primary stakeholders, data sources, and algorithms, (b) outputs for various stakeholders, (c) how outputs were used for action and (d) reflect on challenges and lessons learnt. Outputs were tailored to four main stakeholder groups: four outputs provided direct information to individual citizens, four to complementary systems and researchers, 25 to decision-makers, and 15 informed the public, aiding transparency. Core elements in infrastructure needed for automated surveillance had been in place for more than a decade. The COVID-19 epidemic was a pressure test that allowed us to explore the system’s potential and identify challenges for future pandemic preparedness. The system described here constitutes a model for the future infectious disease surveillance in Denmark. With the current pandemic threat posed by avian influenza viruses, lessons learnt from the COVID-19 pandemic remain topical and relevant.