Risk factors and vectors for SARS-CoV-2 household transmission: a prospective, longitudinal cohort study

The association of COVID- 19 parental immunization and transmission of disease to offspring: a retrospective study

BACKGROUND

The Omicron variant has heightened COVID- 19 infections among children under six, emphasizing the need to understand the role of parental immunization and demographic factors in disease transmission within households.

METHODS

This retrospective observational study included 2321 children under six-year-old from February to May 2022 in Isfahan, Iran. Data were sourced from the recorded PERSIAN Birth Cohort data and telephone interviews, focusing on demographic information, child's COVID- 19 exposure during follow-up, infection, and vaccination status of each family member.

RESULT

Out of 2321 children, the incidence rate of COVID- 19 during the sixth peak was determined to be 46%. Both maternal (X2: 1237.0; p-value < 0.001) and paternal (X2: 1003.1; p-value < 0.001) COVID- 19 infections were identified as significant risk factors for infection of children. Although paternal vaccination showed a statistically significant association with reduced infection rates among children (p = 0.036), maternal immunization did not demonstrate a significantly correlation. After Adjusting covariates, higher odds of child COVID- 19 incidence were associated with maternal infection (OR = 37.74, 95%CI: 24.86- 57.27), paternal infection (OR = 6.50,95% CI: 4.74-8.92), and maternal age older than 30 years old (odds ratio: 0.58, 95% CI: 0.49 to 0.68). Additionally, lower odds of infection were related to living at homes with optimal cleanness (odds ratio: 0.8, 95% CI: 0.6 to 0.9). Although in a crude model, the odds of infection of children in low-income families was 60% more than in moderate- or high-income families; this probability was not statistically significant in the adjusted model.

CONCLUSION

This study underscores the significant role of parental transmission and paternal immunization in child COVID- 19 infections and the dimension of infection rates during the Omicron peak. Regarding the occupational conditions of fathers in our society and the characteristics of the COVID- 19 virus, paternal immunization should be prioritized over maternal immunization to mitigate disease transmission. Also, the sanitation of the home is crucial to prevent of risk of infection in children.

Antiviral Surface Coatings: From Pandemic Lessons to Visible-Light-Activated Films

The increasing need for effective antiviral strategies has led to the development of innovative surface coatings to combat the transmission of viruses via fomites. The aim of this review is to critically assess the efficacy of antiviral coatings in mitigating virus transmission, particularly those activated by visible light. The alarm created by the COVID-19 pandemic, including the initial uncertainty about the mechanisms of its spread, attracted attention to fomites as a possible source of virus transmission. However, later research has shown that surface-dependent infection mechanisms need to be carefully evaluated experimentally. By briefly analyzing virus-surface interactions and their implications, this review highlights the importance of shifting to innovative solutions. In particular, visible-light-activated antiviral coatings that use reactive oxygen species such as singlet oxygen to disrupt viral components have emerged as promising options. These coatings can allow for obtaining safe, continuous, and long-term active biocidal surfaces suitable for various applications, including healthcare environments and public spaces. This review indicates that while the significance of fomite transmission is context-dependent, advances in material science provide actionable pathways for designing multifunctional, visible-light-activated antiviral coatings. These innovations align with the lessons learned from the COVID-19 pandemic and pave the way for sustainable, broad-spectrum antiviral solutions capable of addressing future public health challenges.

Impact of disease severity, age, sex, comorbidity, and vaccination on secondary attack rates of SARS-CoV-2: a global systematic review and meta-analysis

BACKGROUND

Understanding the key drivers of SARS-CoV-2 transmission is essential for shaping effective public health strategies. However, transmission risk is subject to substantial heterogeneity related to disease severity, age, sex, comorbidities, and vaccination status in different population settings and regions. We aimed to quantify the impact of these factors on secondary attack rates (SARs) of SARS-CoV-2 across diverse population settings and regions, and identify key determinants of transmission to inform targeted interventions for improving global pandemic response.

METHODS

To retrieve relevant literature covering the duration of the COVID-19 pandemic, we searched Ovid MEDLINE, Ovid Embase, Web of Science, and the Cochrane COVID-19 Study Register between January 1, 2020 and January 18, 2024 to identify studies estimating SARs of SARS-CoV-2, defined as the proportion of close contacts infected. We pooled SAR estimates using a random-effects model with the Freeman-Tukey double arcsine transformation and derived Clopper-Pearson 95% confidence intervals (CIs). Risk of bias was assessed using a modified Newcastle-Ottawa scale. This study was registered with PROSPERO, CRD42024503782.

RESULTS

A total of 159 eligible studies, involving over 19 million close contacts and 6.8 million cases from 41 countries across five continents, were included in the analysis. SARs increased with disease severity in index cases, ranging from 0.10 (95% CI: 0.06-0.14; I2 = 99.65%) in asymptomatic infection to 0.15 (95% CI: 0.09-0.21; I2 = 92.49%) in those with severe or critical conditions. SARs by age were lowest at 0.20 (95% CI: 0.16-0.23; I2 = 99.44%) for close contacts under 18 years and highest at 0.29 (95% CI: 0.24-0.34; I2 = 99.65%) for index cases aged 65 years or older. Among both index cases and close contacts, pooled SAR estimates were highest for Omicron and lowest for Delta, and declined with increasing vaccine doses. Regionally, North America had the highest SAR at 0.27 (95% CI: 0.24-0.30; I2 = 99.31%), significantly surpassing SARs in Europe (0.19; 95% CI: 0.15-0.25; I2 = 99.99%), Southeast Asia (0.18; 95% CI: 0.13-0.24; I2 = 99.24%), and the Western Pacific (0.11; 95% CI: 0.08-0.15; I2 = 99.95%). Among close contacts with comorbidities, chronic lung disease and hypertension were associated with the highest SARs. No significant association was found between SARs and the sex of either index cases or close contacts.

CONCLUSIONS

Secondary attack rates varied substantially by demographic and regional characteristics of the studied populations. Our findings demonstrate the role of booster vaccinations in curbing transmission, underscoring the importance of maintaining population immunity as variants of SARS-CoV-2 continue to emerge. Effective pandemic responses should prioritise tailored interventions that consider population demographics and social dynamics across different regions.

Preferential apical infection of Caco-2 intestinal cell monolayers by SARS-CoV-2 is associated with damage to cellular barrier integrity: Implications for the pathophysiology of COVID-19

SARS-CoV-2 can infect different organs, including the intestine. In an in vitro model of Caco-2 intestinal cell line, we previously found that SARS-CoV-2 modulates the ACE2 receptor expression and affects the expression of molecules involved in intercellular junctions. To further explore the possibility that the intestinal epithelium can serve as an alternative infection route for SARS-CoV-2, we used a model of polarized monolayers of Caco-2 cells (or co-cultures of two intestinal cell lines: Caco-2 and HT29) grown on the polycarbonate membrane of Transwell inserts, inoculated with the virus either in the upper or lower chamber of culture to determine the tropism of the virus for the apical or basolateral pole of these cells. In both polarized Caco-2 cell monolayers and co-culture Caco-2/HT29 cell monolayer, apical SARS-CoV-2 inoculation was found to be much more effective in establishing infection than basolateral inoculation. In addition, apical SARS-CoV-2 infection triggers monolayer degeneration, as shown by histological examination, measurement of trans-epithelial electrical resistance, and cell adhesion molecule expression. During apical infection, the infectious viruses reach the lower chamber, suggesting either a transcytosis mechanism from the apical side to the basolateral side of cells, a paracellular trafficking of the virus after damage to intercellular junctions in the epithelial barrier, or both. Taken together, these data indicate a preferential tropism of SARS-CoV-2 for the apical pole of the human intestinal tract and suggest that infection via the intestinal lumen leads to a systemic infection.

SARS-CoV-2 infection rates and associated risk factors in healthcare workers: systematic review and meta-analysis

To protect healthcare workforce during the COVID-19 pandemic, rigorous efforts were made to reduce infection rates among healthcare workers (HCWs), especially prior to vaccine availability. This study aimed to investigate the prevalence of SARS-CoV-2 infections among HCWs and identify potential risk factors associated with transmission. We searched MEDLINE, Embase, and Google Scholar from 1 December 2019 to 5 February 2024. From 498 initial records, 190 articles were reviewed, and 63 studies were eligible. ROBINS-E tool revealed a lower risk of bias in several domains; however, some concerns related to confounding and exposure measurement were identified. Globally, 11% (95% confidence interval (CI) 9-13) of 283,932 HCWs were infected with SARS-CoV-2. Infection rates were associated with a constellation of risk factors and major circulating SARS-CoV-2 variants. Household exposure (odds ratio (OR) 7.07; 95% CI 3.93-12.73), working as a cleaner (OR 2.72; 95% CI 1.39-5.32), occupational exposure (OR 1.79; 95% CI 1.49-2.14), inadequate training on infection prevention and control (OR 1.46; 95% CI 1.14-1.87), insufficient use of personal protective equipment (OR 1.45; 95% CI 1.14-1.84), performing aerosol generating procedures (OR 1.36; 95% CI 1.21-1.52) and inadequate hand hygiene (OR 1.17; 95% CI 0.79-1.73) were associated with an increased SARS-CoV-2 infection. Conversely, history of quarantine (OR 0.23; 95% CI 0.08-0.60) and frequent decontamination of high touch areas (OR 0.52; 95% CI 0.42-0.64) were protective factors against SARS-CoV-2 infection. This study quantifies the substantial global burden of SARS-CoV-2 infection among HCWs. We underscore the urgent need for effective infection prevention and control measures, particularly addressing factors such as household exposure and occupational practices by HCWs, including cleaning staff.

Inferring transmission risk of respiratory viral infection from the viral load kinetics of SARS-CoV-2, England, 2020 to 2021 and influenza A virus, Hong Kong, 2008 to 2012

BackgroundInfectiousness of respiratory viral infections is quantified as plaque forming units (PFU), requiring resource-intensive viral culture that is not routinely performed. We hypothesised that RNA viral load (VL) decline time (e-folding time) in people might serve as an alternative marker of infectiousness.AimThis study's objective was to evaluate the association of RNA VL decline time with RNA and PFU VL area under the curve (AUC) and transmission risk for SARS-CoV-2 and influenza A virus.MethodsIn SARS-CoV-2 and influenza A virus community cohorts, viral RNA was quantified by reverse transcription quantitative PCR in serial upper respiratory tract (URT)-samples collected within households after an initial household-member tested positive for one virus. We evaluated correlations between RNA VL decline time and RNA and PFU-VL AUC. Associations between VL decline time and transmission risk in index-contact pairs were assessed.ResultsIn SARS-CoV-2 cases, we observed positive correlations between RNA VL decline time and RNA and PFU VL AUC with posterior probabilities 1 and 0.96 respectively. In influenza A cases a positive correlation between RNA VL decline time and RNA VL AUC was observed, with posterior probability of 0.87. Index case VL decline times one standard deviation above the cohort-mean showed a relative increase in secondary attack rates of 39% (95% credible interval (CrI): -6.9 to 95%) for SARS-CoV-2 and 25% (95% CrI: -11 to 71%) for influenza A virus.ConclusionWe identify VL decline time as a potential marker of infectiousness and transmission risk for SARS-CoV-2 and influenza A virus. Early ascertainment of VL kinetics as part of surveillance of new viruses or variants could inform public health decision making.

An ultra-early, transient interferon-associated innate immune response associates with protection from SARS-CoV-2 infection despite exposure

BACKGROUND

A proportion of individuals exposed to respiratory viruses avoid contracting detectable infection. We tested the hypothesis that early innate immune responses associate with resistance to detectable infection in close contacts of COVID-19 cases.

METHODS

48 recently-exposed household contacts of symptomatic COVID-19 cases were recruited in London, UK between May 2020 and March 2021 through a prospective, longitudinal observational study. Blood and nose and throat swabs were collected during the acute period of index case viral shedding and longitudinally thereafter. Magnitude of SARS-CoV-2 exposure was quantified, and serial PCR and serological assays used to determine infection status of contacts. Whole-blood RNA-seq was performed and analysed to identify transcriptomic signatures of early infection and resistance to infection.

FINDINGS

24 highly-exposed household contacts became PCR-positive and seropositive whilst 24 remained persistently PCR-negative and seronegative. A 96-gene transcriptomic signature of early SARS-CoV-2 infection was identified using RNA-seq of longitudinal blood samples from PCR-positive contacts. This signature was dominated by interferon-associated genes and expression correlated positively with viral load. Elevated expression of this 96-gene signature was also observed during exposure in 25% (6/24) of persistently PCR-negative, seronegative contacts. PCR-negative contacts with elevated signature expression had higher-magnitude SARS-CoV-2 exposure compared to those with low signature expression. We validated this signature in SARS-CoV-2-infected individuals in two independent cohorts. In naturally-exposed healthcare workers (HCWs) we found that 7/58 (12%) PCR-negative HCWs exhibited elevated signature expression. Comparing gene-signature expression in SARS-CoV-2 Controlled Human Infection Model (CHIM) volunteers pre- and post-inoculation, we observed that 14 signature genes were transiently upregulated as soon as 6 hr post-inoculation in PCR-negative volunteers, while in PCR-positive volunteers gene-signature upregulation did not occur until 3 days later.

INTERPRETATION

Our interferon-associated signature of early SARS-CoV-2 infection characterises a subgroup of exposed, uninfected contacts in three independent cohorts who may have successfully aborted infection prior to induction of adaptive immunity. The earlier transient upregulation of signature genes in PCR-negative compared to PCR-positive CHIM volunteers suggests that ultra-early interferon-associated innate immune responses correlate with, and may contribute to, protection against SARS-CoV-2 infection.

FUNDING

This work was supported by the NIHR Health Protection Research Unit in Respiratory Infections, United Kingdom, NIHR Imperial College London, United Kingdom (Grant number: NIHR200927; AL) in partnership with the UK Health Security Agency and the NIHR Medical Research Council (MRC), United Kingdom (Grant number: MR/X004058/1). Support for sequencing was provided by the Imperial BRC Genomics Facility which is funded by the NIHR, United Kingdom. The development of the hybrid DABA assay used for quantification of SARS-CoV-2 anti-Spike RBD antibodies was supported by the MRC (MC_PC_19078).

Performance of rapid antigen tests to detect SARS-CoV-2 variant diversity and correlation with viral culture positivity: implication for diagnostic development and future public health strategies

Antigen-based rapid diagnostic tests (Ag-RDTs) provide timely results, are simple to use, and are less expensive than molecular assays. Recent studies suggest that antigen-based testing aligns with virus culture-based results (a proxy of contagiousness at the peak viral phase of illness); however, the performance of Ag-RDTs for newer SARS-CoV-2 variants is unclear. In this study, we (i) assessed the performance of Ag-RDTs and diagnostic antibodies to detect a range of SARS-CoV-2 variants and (ii) determined whether Ag-RDT results correlated with culture positivity. We noted only minor differences in the limit of detection by variant for all assays, and we demonstrated consistent antibody affinity to the N protein among the different variants. We observed moderate to high sensitivity (46.8%-83.9%) for Ag-RDTs when compared to PCR positivity (100%), and all variants were assessed on each assay. Ag-RDT sensitivity and PCR Ct showed an inverse correlation with the detection of viable virus. Collectively, our results demonstrate that commercially available Ag-RDTs offer variable sensitivity compared to PCR, show similar diagnostic validity across variants, and may predict the risk of transmissibility. These findings may be used to support more tailored SARS-CoV-2 isolation strategies, particularly if other studies clarify the direct association between Ag-RDT positivity and transmission risk. The apparent trade-off between sensitivity in the detection of any PCR-positive infection and concordance with infectious virus positivity may also inform new RDT diagnostic development strategies for SARS-CoV-2 and other epidemic respiratory pathogens.

IMPORTANCE

Despite the availability of vaccines, COVID-19 continues to be a major health concern, and antigen-based rapid diagnostic tests (Ag-RDTs) are commonly used as point-of-care or at-home diagnostic tests. In this study, we evaluated the performance of two commercially available Ag-RDTs and a research Ag-RDT to detect multiple SARS-CoV-2 variants using upper respiratory tract swab samples from clinical COVID-19 cases. Furthermore, we determined whether Ag-RDT results correlated with culture positivity, a potential proxy of viral transmissibility. Our results have important implications to inform future testing and response strategies during periods of high COVID-19 transmission with new variants.

SARS-CoV-2 human challenge reveals biomarkers that discriminate early and late phases of respiratory viral infections

Blood transcriptional biomarkers of acute viral infections typically reflect type 1 interferon (IFN) signalling, but it is not known whether there are biological differences in their regulation that can be leveraged for distinct translational applications. We use high frequency sampling in the SARS-CoV-2 human challenge model to show induction of IFN-stimulated gene (ISG) expression with different temporal and cellular profiles. MX1 gene expression correlates with a rapid and transient wave of ISG expression across all cell types, which may precede PCR detection of replicative infection. Another ISG, IFI27, shows a delayed but sustained response restricted to myeloid cells, attributable to gene and cell-specific epigenetic regulation. These findings are reproducible in experimental and naturally acquired infections with influenza, respiratory syncytial virus and rhinovirus. Blood MX1 expression is superior to IFI27 expression for diagnosis of early infection, as a correlate of viral load and for discrimination of virus culture positivity. Therefore, MX1 expression offers potential to stratify patients for antiviral therapy or infection control interventions. Blood IFI27 expression is superior to MX1 expression for diagnostic accuracy across the time course of symptomatic infection and thereby, offers higher diagnostic yield for respiratory virus infections that incur a delay between transmission and testing.

Incorporation of Silver into Sulfate Groups Enhances Antimicrobial and Antiviral Effects of Fucoidan

The COVID-19 pandemic has significantly impacted our daily lives. Routine infection-control measures present an effective preventive strategy for a new infectious disease outbreak. Fucoidan, a fucose-rich sulfated polysaccharide found in brown algae, exhibits antiviral activity. Moreover, fucoidan exerts an antimicrobial effect; however, it requires considerably higher concentrations than those needed for its antiviral effect. In this study, we aimed to enhance the antimicrobial activity of fucoidan and prepared a fucoidan silver salt (Ag-Fuc) by incorporating silver ions into the sulfate groups of Yakult Fucoidan derived from Cladosiphon okamuranus Tokida. The fucoidan exhibited a weak inhibitory effect on Escherichia coli growth at significantly higher concentrations, whereas Ag-Fuc inhibited the growth of E. coli and Staphylococcus epidermidis at concentrations comparable to those required for its antiviral effects. Moreover, Ag-Fuc inhibited the growth of Cladosporium cladosporioides. Infections of human cells with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza A virus were more effectively inhibited by lower concentrations of Ag-Fuc compared with fucoidan. Overall, silver ions added to the sulfate groups induced strong antimicrobial activity and enhanced the antiviral effect of fucoidan. We suggest a wide application of Ag-Fuc as a routine preventive material to avoid new infectious disease pandemics.

Racial and Ethnic Disparities in Age-Specific All-Cause Mortality During the COVID-19 Pandemic

Importance

The end of the COVID-19 public health emergency (PHE) provides an opportunity to fully describe pandemic-associated racial and ethnic mortality disparities. Age-specific excess mortality differences have important downstream implications, especially in minoritized race and ethnicity populations.

Objectives

To characterize overall and age-specific all-cause excess mortality by race and ethnicity during the COVID-19 PHE and assess whether measured differences reflected changes from prepandemic disparities.

Design, Setting, and Participants

This cross-sectional study analyzed data of all US residents and decedents during the COVID-19 PHE, aggregated by observed race and ethnicity (at time of death) and age. Statistical analysis was performed from March 2020 to May 2023.

Exposures

COVID-19 PHE period (March 2020 to May 2023).

Main Outcomes and Measures

All-cause excess mortality (incident rates, observed-to-expected ratios) and all-cause mortality relative risks before and during the PHE.

Results

For the COVID-19 PHE period, data for 10 643 433 death certificates were available; mean (SD) decedent age was 72.7 (17.9) years; 944 318 (8.9%) were Hispanic; 78 973 (0.7%) were non-Hispanic American Indian or Alaska Native; 288 680 (2.7%) were non-Hispanic Asian, 1 374 228 (12.9%) were non-Hispanic Black or African American, 52 905 (0.5%) were non-Hispanic more than 1 race, 15 135 (0.1%) were non-Hispanic Native Hawaiian or Other Pacific Islander, and 7 877 996 (74.1%) were non-Hispanic White. More than 1.38 million all-cause excess deaths (observed-to-expected ratio, 1.15 [95% CI, 1.12-1.18]) occurred, corresponding to approximately 23 million years of potential life lost (YPLL) during the pandemic. For the total population (all ages), the racial and ethnic groups with the highest observed-to-expected all-cause mortality ratios were the American Indian or Alaska Native (1.34 [95% CI, 1.31-1.37]) and Hispanic (1.31 [95% CI, 1.27-1.34]) populations. However, higher ratios were observed in the US population aged 25 to 64 years (1.20 [95% CI, 1.18-1.22]), greatest among the American Indian or Alaska Native (1.45 [95% CI, 1.42-1.48]), Hispanic (1.40 [95% CI, 1.38-1.42]), and Native Hawaiian or Other Pacific Islander (1.39 [95% CI, 1.34-1.44]) groups. In the total population aged younger than 25 years, the Black population accounted for 51.1% of excess mortality, despite representing 13.8% of the population. Had the rate of excess mortality observed among the White population been observed among the total population, more than 252 000 (18.3%) fewer excess deaths and more than 5.2 million (22.3%) fewer YPLL would have occurred.

Conclusions and Relevance

In this cross-sectional study of the US population during the COVID-19 PHE, excess mortality occurred in all racial and ethnic groups, with disparities affecting several minoritized populations. The greatest relative increases occurred in populations aged 25 to 64 years. Documented differences deviated from prepandemic disparities.

An outbreak of SARS-CoV-2 in a public-facing office in England

BACKGROUND

An outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with an attack rate of 55% (22/40 workers) occurred at a public-facing office in England from August to September 2021. Published evidence regarding outbreaks in office workplaces remains limited.

AIMS

To describe an investigation of workplace- and worker-related risk factors following an outbreak of SARS-CoV-2 in a public-facing office.

METHODS

The COVID-19 (coronavirus disease 2019) Outbreak Investigation to Understand Transmission (COVID-OUT) study undertook an investigation of the outbreak. This included surface sampling, occupational environmental assessment, molecular and serological testing of workers, and detailed questionnaires.

RESULTS

Despite existing COVID-19 control measures, surface sampling conducted during a self-imposed 2-week temporary office closure identified viral contamination (10/60 samples, 17% positive), particularly in a small, shared security office (6/9, 67% positive) and on a window handle in one open-plan office. Targeted enhanced cleaning was, therefore, undertaken before the office reopened. Repeat surface sampling after this identified only one positive (2%) sample. Ventilation was deemed adequate using carbon dioxide monitoring (typically ≤1000 ppm). Twelve workers (30%) responded to the COVID-OUT questionnaire, and all had been vaccinated with two doses. One-third of respondents (4/12) reported direct physical or close contact with members of the public; of these, 75% (3/4) reported a divider/screen between themselves and members of the public.

CONCLUSIONS

The results highlight the potential utility of surface sampling to identify SARS-CoV-2 control deficiencies and the importance of evolving, site-specific risk assessments with layered COVID-19 mitigation strategies.

Doff Thy Gown-Shedding Contact Precautions for COVID-19

SARS-CoV-2 is predominantly transmitted through aerosols (ie, airborne transmission); however, the US Centers for Disease Control and Prevention continue to recommend the use of contact precautions (a gown and gloves) for the care of patients with COVID-19. Infection-prevention guidelines should reflect the current science and eliminate this wasteful practice.

No evidence that ACE2 or TMPRSS2 drive population disparity in COVID risks

Early in the SARS-CoV2 pandemic, in this journal, Hou et al. (BMC Med 18:216, 2020) interpreted public genotype data, run through functional prediction tools, as suggesting that members of particular human populations carry potentially COVID-risk-increasing variants in genes ACE2 and TMPRSS2 far more often than do members of other populations. Beyond resting on predictions rather than clinical outcomes, and focusing on variants too rare to typify population members even jointly, their claim mistook a well known artifact (that large samples reveal more of a population's variants than do small samples) as if showing real and congruent population differences for the two genes, rather than lopsided population sampling in their shared source data. We explain that artifact, and contrast it with empirical findings, now ample, that other loci shape personal COVID risks far more significantly than do ACE2 and TMPRSS2-and that variation in ACE2 and TMPRSS2 per se unlikely exacerbates any net population disparity in the effects of such more risk-informative loci.

COVID-19 infections in English schools and the households of students and staff 2020-21: a self-controlled case-series analysis

BACKGROUND

The role of children and staff in SARS-CoV-2 transmission outside and within households is still not fully understood when large numbers are in regular, frequent contact in schools.

METHODS

We used the self-controlled case-series method during the alpha- and delta-dominant periods to explore the incidence of infection in periods around a household member infection, relative to periods without household infection, in a cohort of primary and secondary English schoolchildren and staff from November 2020 to July 2021.

RESULTS

We found the relative incidence of infection in students and staff was highest in the 1-7 days following household infection, remaining high up to 14 days after, with risk also elevated in the 6--12 days before household infection. Younger students had a higher relative incidence following household infection, suggesting household transmission may play a more prominent role compared with older students. The relative incidence was also higher among students in the alpha variant dominant period.

CONCLUSIONS

This analysis suggests SARS-CoV2 infection in children, young people and staff at English schools were more likely to be associated with within-household transmission than from outside the household, but that a small increased risk of seeding from outside is observed.

How effective is the BNT162b2 mRNA vaccine against SARS-CoV-2 transmission and infection? A national programme analysis in Monaco, July 2021 to September 2022

BACKGROUND

We quantified SARS-CoV-2 dynamics in different community settings and the direct and indirect effect of the BNT162b2 mRNA vaccine in Monaco for different variants of concern (VOC).

METHODS

Between July 2021 and September 2022, we prospectively investigated 20,443 contacts from 6320 index cases using data from the Monaco COVID-19 Public Health Programme. We calculated secondary attack rates (SARs) in households (n = 13,877), schools (n = 2508) and occupational (n = 6499) settings. We used binomial regression with a complementary log-log link function to measure adjusted hazard ratios (aHR) and vaccine effectiveness (aVE) for index cases to infect contacts and contacts to be infected in households.

RESULTS

In households, the SAR was 55% (95% CI 54-57) and 50% (48-51) among unvaccinated and vaccinated contacts, respectively. The SAR was 32% (28-36) and 12% (10-13) in workplaces, and 7% (6-9) and 6% (3-10) in schools, among unvaccinated and vaccinated contacts respectively. In household, the aHR was lower in contacts than in index cases (aHR 0.68 [0.55-0.83] and 0.93 [0.74-1.1] for delta; aHR 0.73 [0.66-0.81] and 0.89 [0.80-0.99] for omicron BA.1&2, respectively). Vaccination had no significant effect on either direct or indirect aVE for omicron BA.4&5. The direct aVE in contacts was 32% (17, 45) and 27% (19, 34), and for index cases the indirect aVE was 7% (- 17, 26) and 11% (1, 20) for delta and omicron BA.1&2, respectively. The greatest aVE was in contacts with a previous SARS-CoV-2 infection and a single vaccine dose during the omicron BA.1&2 period (45% [27, 59]), while the lowest were found in contacts with either three vaccine doses (aVE - 24% [- 63, 6]) or one single dose and a previous SARS-CoV-2 infection (aVE - 36% [- 198, 38]) during the omicron BA.4&5 period.

CONCLUSIONS

Protection conferred by the BNT162b2 mRNA vaccine against transmission and infection was low for delta and omicron BA.1&2, regardless of the number of vaccine doses and previous SARS-CoV-2 infection. There was no significant vaccine effect for omicron BA.4&5. Health authorities carrying out vaccination campaigns should bear in mind that the current generation of COVID-19 vaccines may not represent an effective tool in protecting individuals from either transmitting or acquiring SARS-CoV-2 infection.

Prevalence of SARS-CoV-2-specific antibodies in a sample of the Lithuanian population-based study in Spring 2023

Objectives

Despite positive trends in SARS-CoV-2 epidemiology, seroprevalence surveys remain an important tool for estimating the magnitude of the COVID-19 pandemic. This study aimed to investigate the prevalence of IgG antibodies against SARS-CoV-2 nucleocapsid (N) and spike (S) proteins in a sample of the Lithuanian population (N = 517) and evaluate how the pattern of seropositivity correlates with the levels of SARS-CoV-2 infection and vaccination.

Methods

Study participants (aged 18-88 years) filled in the questionnaire self-reporting their demographic-social variables, health status, and SARS-CoV-2-related status. The anti-S and anti-N IgG levels were estimated using a microarray ELISA test.

Results

After several pandemic waves and vaccination campaign, the seroprevalence of SARS-CoV-2-specific IgG in the analyzed sample was 97.87 % by March-May 2023. We determined the 96.91 % prevalence of anti-S and 58.03 % prevalence of anti-N IgG. The majority of study participants (71.18 %) had hybrid immunity induced by vaccination and SARS-CoV-2 infection. 20.3 % of study participants were anti-N IgG positive without reporting any previous symptoms or a positive SARS-CoV-2 test. A decline of anti-N IgG positivity within 9 months after infection was observed.

Conclusions

This study demonstrates high total seroprevalence in March-May 2023 in all age groups indicating a widely established humoral immunity against SARS-CoV-2 in Lithuania.

Concordance between SARS-CoV-2 index individuals and their household contacts on index individual COVID-19 transmission cofactors: a comparison of self-reported and contact-reported information

BACKGROUND

Following the outbreak of the COVID-19 pandemic, several clinical trials have evaluated postexposure prophylaxis (PEP) among close contacts of an index individual with a confirmed SARS-CoV-2 infection. Because index individuals do not directly inform the efficacy of prevention interventions, they are seldom enrolled in COVID-19 PEP studies. However, adjusting for prognostic covariates such as an index individual's COVID-19 illness and risk behaviors can increase precision in PEP efficacy estimates, so approaches to accurately collecting this information about the index individual are needed. This analysis aimed to assess whether surveying household contacts captures the same information as surveying the index individual directly.

METHODS

REGN 2069/CoVPN 3502, a randomized controlled trial of COVID-19 PEP, enrolled household contacts of SARS-CoV-2 index individuals. CoVPN 3502-01 retrospectively enrolled and surveyed the index individuals. We compared responses to seven similar questions about the index individuals' transmission cofactors that were asked in both studies. We estimated the percent concordance between index individuals and their household contacts on each question, with 50% concordance considered equivalent to random chance.

RESULTS

Concordance between index individuals and contacts was high on the most objective questions, approximately 97% (95% CI: 90-99%) for index individual age group and 96% (88-98%) for hospitalization. Concordance was moderate for symptoms, approximately 85% (75-91%). Concordance on questions related to the index individual's behavior was only slightly better or no better than random: approximately 62% (51-72%) for whether they received COVID-19 treatment, 68% (57-77%) for sharing a bedroom, 70% (59-79%) for sharing a common room, and 49% (39-60%) for mask wearing at home. However, while contacts were surveyed within 96 h of the index individual testing positive for SARS-CoV-2, the median time to enrollment in CoVPN 3502-01 was 240 days, which may have caused recall bias in our results.

CONCLUSIONS

Our results suggest a need to survey index individuals directly in order to accurately capture their transmission cofactors, rather than relying on their household contacts to report on their behavior. The lag in enrolling participants into CoVPN 3502-01 also highlights the importance of timely enrollment to minimize recall bias.

A 17-month longitudinal surface sampling study carried out on public transport vehicles operating in England during the COVID-19 pandemic identified low levels of SARS-CoV-2 RNA contamination

AIMS

To monitor severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) RNA contamination in vehicles operating in England during the pandemic, to better understand transmission risk of SARS-CoV-2 on public transport.

METHODS AND RESULTS

We collected 1314 surface samples between December 2020 and April 2022 on trains and buses managed by five different transport operators. The presence of SARS-CoV-2 RNA was investigated through reverse transcription polymerase chain reaction (RT-PCR). SARS-CoV-2 RNA was found on 197 (15%) of the 1314 surfaces sampled, including seat head rests, handholds, and air extract grilles, but the levels of RNA recovered on those samples (median value of 23.4, interquartile range: 14.3-35.4, N gene copies per extraction) made the presence of infectious virus at the time of sampling extremely unlikely. However, detection rates varied over time with peaks broadly coinciding with times of high community transmission, when it was more likely that people infected with SARS-CoV-2 were travelling on public transport.

CONCLUSION

During the pandemic, and as in other public spaces, low levels of SARS-CoV-2 RNA were found on surfaces associated with public transport.

A narrative review of alternative transmission routes of COVID 19: what we know so far

The Coronavirus disease 19 (COVID-19) pandemics, caused by severe acute respiratory syndrome coronaviruses, SARS-CoV-2, represent an unprecedented public health challenge. Beside person-to-person contagion via airborne droplets and aerosol, which is the main SARS-CoV-2's route of transmission, alternative modes, including transmission via fomites, food and food packaging, have been investigated for their potential impact on SARS-CoV-2 diffusion. In this context, several studies have demonstrated the persistence of SARS-CoV-2 RNA and, in some cases, of infectious particles on exposed fomites, food and water samples, confirming their possible role as sources of contamination and transmission. Indeed, fomite-to-human transmission has been demonstrated in a few cases where person-to-person transmission had been excluded. In addition, recent studies supported the possibility of acquiring COVID-19 through the fecal-oro route; the occurrence of COVID-19 gastrointestinal infections, in the absence of respiratory symptoms, also opens the intriguing possibility that these cases could be directly related to the ingestion of contaminated food and water. Overall, most of the studies considered these alternative routes of transmission of low epidemiological relevance; however, it should be considered that they could play an important role, or even be prevalent, in settings characterized by different environmental and socio-economic conditions. In this review, we discuss the most recent findings regarding SARS-CoV-2 alternative transmission routes, with the aim to disclose what is known about their impact on COVID-19 spread and to stimulate research in this field, which could potentially have a great impact, especially in low-resource contexts.

Environmental and behavioral factors associated with household transmission of SARS-CoV-2 in children and adolescents

Objective

To analyze the association between risk behaviors and environmental factors and SARS-CoV-2 infection in children and adolescents in the family environment.

Methods

Cross-sectional study. A total of 267 children and adolescents aged 5-19 years who have contact with COVID-19-positive essential workers were tested between June and October 2020. Behavioral and environmental variables associated with SARS-CoV-2 infection were investigated. Association between these variables was performed using Poisson regression.

Results

SARS-CoV-2 prevalence was 25.1%. Following the confirmation of COVID-19 diagnosis of the index case, 92.1% of adults reported hand hygiene and 83.5% showed habits of respiratory etiquette. However, 12.7% wore masks in common areas of the residence before COVID-19. Sharing common objects was a risk factor for SARS-CoV-2 infection in the sample.

Conclusion

Sharing objects among family members was identified as a risk factor associated with SARS-CoV-2 infection in children and adolescents who lived with infected adults. There was high frequency of hand hygiene and low prevalence of mask use.

Non-pharmaceutical interventions for COVID-19: a systematic review on environmental control measures

The purpose of this review was to identify the effectiveness of environmental control (EC) non-pharmaceutical interventions (NPIs) in reducing transmission of SARS-CoV-2 through conducting a systematic review. EC NPIs considered in this review are room ventilation, air filtration/cleaning, room occupancy, surface disinfection, barrier devices, [Formula: see text] monitoring and one-way-systems. Systematic searches of databases from Web of Science, Medline, EMBASE, preprint servers MedRxiv and BioRxiv were conducted in order to identify studies reported between 1 January 2020 and 1 December 2022. All articles reporting on the effectiveness of ventilation, air filtration/cleaning, room occupancy, surface disinfection, barrier devices, [Formula: see text] monitoring and one-way systems in reducing transmission of SARS-CoV-2 were retrieved and screened. In total, 13 971 articles were identified for screening. The initial title and abstract screening identified 1328 articles for full text review. Overall, 19 references provided evidence for the effectiveness of NPIs: 12 reported on ventilation, 4 on air cleaning devices, 5 on surface disinfection, 6 on room occupancy and 1 on screens/barriers. No studies were found that considered the effectiveness of [Formula: see text] monitoring or the implementation of one-way systems. Many of these studies were assessed to have critical risk of bias in at least one domain, largely due to confounding factors that could have affected the measured outcomes. As a result, there is low confidence in the findings. Evidence suggests that EC NPIs of ventilation, air cleaning devices and reduction in room-occupancy may have a role in reducing transmission in certain settings. However, the evidence was usually of low or very low quality and certainty, and hence the level of confidence ascribed to this conclusion is low. Based on the evidence found, it was not possible to draw any specific conclusions regarding the effectiveness of surface disinfection and the use of barrier devices. From these results, we further conclude that community agreed standards for well-designed epidemiological studies with low risk of bias are needed. Implementation of such standards would enable more confident assessment in the future of the effectiveness of EC NPIs in reducing transmission of SARS-CoV-2 and other pathogens in real-world settings. This article is part of the theme issue 'The effectiveness of non-pharmaceutical interventions on the COVID-19 pandemic: the evidence'.

Factors associated with household transmission of SARS-CoV-2 omicron variant to health care workers: A retrospective cohort study

AIM

The aim of this study was to determine the risk factors for household transmission of the omicron variant of SARS-CoV-2.

BACKGROUND

The household infection rate has been reported to be higher for the omicron variant than for non-omicron variants of SARS-CoV-2. Determination of the risk factors for household transmission of the omicron variant is therefore important.

DESIGN

A Retrospective Cohort Study was conducted.

METHODS

When family members of health care workers (HCWs) were found to be infected with SARS-CoV-2, the HCWs had to receive two nucleic acid amplification tests for SARS-CoV-2: immediately after and 5 to 10 days after the onset of COVID-19 in the family members. Risk factors of household transmission were analysed by comparing cases (HCWs infected with SARS-CoV-2) and controls (HCWs not infected with SARS-CoV-2) using multivariable analysis.

RESULTS

Unvaccinated status (OR: 3.97), age of index cases (≤6 years) (OR: 1.94) and staying at home with index cases (OR: 10.18) were risk factors for household transmission.

CONCLUSION

If there is a strong desire to avoid household infection, family members infected with SARS-CoV-2 should live separately during the period of viral shedding.

Stability of SARS-CoV-2 on Commercial Aircraft Interior Surfaces with Implications for Effective Control Measures

BACKGROUND

The COVID-19 pandemic from 2019 to 2022 devastated many aspects of life and the economy, with the commercial aviation industry being no exception. One of the major concerns during the pandemic was the degree to which the internal aircraft environment contributed to virus transmission between humans and, in particular, the stability of SARS-CoV-2 on contact surfaces in the aircraft cabin interior.

METHOD

In this study, the stability of various major strains of SARS-CoV-2 on interior aircraft surfaces was evaluated using the TCID50 assessment.

RESULTS

In contrast to terrestrial materials, SARS-CoV-2 was naturally less stable on common contact points in the aircraft interior, and, over a 4 h time period, there was a 90% reduction in culturable virus. Antiviral and surface coatings were extremely effective at mitigating the persistence of the virus on surfaces; however, their benefit was diminished by regular cleaning and were ineffective after 56 days of regular use and cleaning. Finally, successive strains of SARS-CoV-2 have not evolved to be more resilient to survival on aircraft surfaces.

CONCLUSIONS

We conclude that the mitigation strategies for SARS-CoV-2 on interior aircraft surfaces are more than sufficient, and epidemiological evidence over the past three years has not found that surface spread is a major route of transmission.