Antibody and T cell responses against wild-type and Omicron SARS-CoV-2 after third-dose BNT162b2 in adolescents.

The high effectiveness of the third dose of BNT162b2 in healthy adolescents against Omicron BA.1 has been reported in some studies, but immune responses conferring this protection are not yet elucidated. In this analysis, our study (NCT04800133) aims to evaluate the humoral and cellular responses against wild-type and Omicron (BA.1, BA.2 and/or BA.5) SARS-CoV-2 before and after a third dose of BNT162b2 in healthy adolescents. At 5 months after 2 doses, S IgG, S IgG Fc receptor-binding, and neutralising antibody responses waned significantly, yet neutralising antibodies remained detectable in all tested adolescents and S IgG avidity increased from 1 month after 2 doses. The antibody responses and S-specific IFN-γ+ and IL-2+ CD8+ T cell responses were significantly boosted in healthy adolescents after a homologous third dose of BNT162b2. Compared to adults, humoral responses for the third dose were non-inferior or superior in adolescents. The S-specific IFN-γ+ and IL-2+ CD4+ and CD8+ T cell responses in adolescents and adults were comparable or non-inferior. Interestingly, after 3 doses, adolescents had preserved S IgG, S IgG avidity, S IgG FcγRIIIa-binding, against Omicron BA.2, as well as preserved cellular responses against BA.1 S and moderate neutralisation levels against BA.1, BA.2 and BA.5. Sera from 100 and 96% of adolescents tested at 1 and 5 months after two doses could also neutralise BA.1. Our study found high antibody and T cell responses, including potent cross-variant reactivity, after three doses of BNT162b2 vaccine in adolescents in its current formulation, suggesting that current vaccines can be protective against symptomatic Omicron disease.

Resurgence of Omicron BA.2 in SARS-CoV-2 infection-naive Hong Kong.

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 stringent public health and social measures (PHSMs). By analyzing genome sequences and epidemiological data, we reconstructed the epidemic trajectory of BA.2 wave and found that the initial BA.2 community transmission emerged from cross-infection within hotel quarantine. The rapid implementation of PHSMs suppressed early epidemic growth but the effective reproduction number (Re) increased again during the Spring festival in early February and remained around 1 until early April. Independent estimates of point prevalence and incidence using phylodynamics also showed extensive superspreading at this time, which likely contributed to the rapid expansion of the epidemic. Discordant inferences based on genomic and epidemiological data underscore the need for research to improve near real-time epidemic growth estimates by combining multiple disparate data sources to better inform outbreak response policy.

Within-host genetic diversity of SARS-CoV-2 lineages in unvaccinated and vaccinated individuals.

Viral and host factors can shape SARS-CoV-2 evolution. However, little is known about lineage-specific and vaccination-specific mutations that occur within individuals. Here, we analysed deep sequencing data from 2,820 SARS-CoV-2 respiratory samples with different viral lineages to describe the patterns of within-host diversity under different conditions, including vaccine-breakthrough infections. In unvaccinated individuals, variant of Concern (VOC) Alpha, Delta, and Omicron respiratory samples were found to have higher within-host diversity and were under neutral to purifying selection at the full genome level compared to non-VOC SARS-CoV-2. Breakthrough infections in 2-dose or 3-dose Comirnaty and CoronaVac vaccinated individuals did not increase levels of non-synonymous mutations and did not change the direction of selection pressure. Vaccine-induced antibody or T cell responses did not appear to have significant impact on within-host SARS-CoV-2 sequence diversification. Our findings suggest that vaccination does not increase exploration of SARS-CoV-2 protein sequence space and may not facilitate emergence of viral variants.

Immunogenicity against wild-type and Omicron SARS-CoV-2 after a third dose of inactivated COVID-19 vaccine in healthy adolescents.

Introduction: Two doses of inactivated SARS-CoV-2 vaccine CoronaVac cannot elicit high efficacy against symptomatic COVID-19, especially against the Omicron variant, but that can be improved by a third dose in adults. The use of a third dose of CoronaVac in adolescents may be supported by immunobridging studies in the absence of efficacy data. Methods: With an immunobridging design, our study (NCT04800133) tested the non-inferiority of the binding and neutralizing antibodies and T cell responses induced by a third dose of CoronaVac in healthy adolescents (N=94, median age 14.2 years, 56% male) compared to adults (N=153, median age 48.1 years, 44% male). Responses against wild-type (WT) and BA.1 SARS-CoV-2 were compared in adolescents. Safety and reactogenicity were also monitored. Results: A homologous third dose of CoronaVac further enhanced antibody response in adolescents compared to just 2 doses. Adolescents mounted non-inferior antibody and T cell responses compared to adults. Although S IgG and neutralizing antibody responses to BA.1 were lower than to WT, they remained detectable in 96% and 86% of adolescents. T cell responses to peptide pools spanning only the mutations of BA.1 S, N and M in adolescents were preserved, increased, and halved compared to WT respectively. No safety concerns were identified. Discussion: The primary vaccination series of inactivated SARS-CoV-2 vaccines for adolescents should include 3 doses for improved humoral immunogenicity.

Ethics of college vaccine mandates, using reasonable comparisons.

In the paper 'COVID-19 vaccine boosters for young adults: a risk-benefit assessment and ethical analysis of mandate policies at universities,' Bardosh et al argued that college mandates of the COVID-19 booster vaccine are unethical. The authors came to this conclusion by performing three different sets of comparisons of benefits versus risks using referenced data and argued that the harm outweighs the risk in all three cases. In this response article, we argue that the authors frame their arguments by comparing values that are not scientifically or reasonably comparable and that the authors used values that represent grossly different risk profiles and grouped them into a set of figures to create an illusion of fair comparisons. We argue that absent the falsely skewed portrayals of a higher level of risk over benefit in their misrepresented figures, the five ethical arguments they presented completely fall apart.

Slow waning of antibodies following a third dose of BNT162b2 in adults who had previously received two doses of inactivated vaccine.

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 robust antibody responses to the ancestral strain at six months after receipt of BNT162b2. Antibody responses to Omicron BA.2 by live virus neutralization were weaker after the third dose and had declined to a low level by six months.

Viral burden rebound in hospitalised patients with COVID-19 receiving oral antivirals in Hong Kong: a population-wide retrospective cohort study.

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 of hospitalised patients with a confirmed diagnosis of COVID-19 in Hong Kong, China, for an observation period from Feb 26 to July 3, 2022 (during the omicron BA.2.2 variant wave). Adult patients (age ≥18 years) admitted 3 days before or after a positive COVID-19 test were selected from medical records held by the Hospital Authority of Hong Kong. We included patients with non-oxygen-dependent COVID-19 at baseline receiving either molnupiravir (800 mg twice a day for 5 days), nirmatrelvir-ritonavir (nirmatrelvir 300 mg with ritonavir 100 mg twice a day for 5 days), or no oral antiviral treatment (control group). Viral burden rebound was defined as a reduction in cycle threshold (Ct) value (≥3) on quantitative RT-PCR test between two consecutive measurements, with such decrease sustained in an immediately subsequent Ct measurement (for those patients with ≥3 Ct measurements). Logistic regression models were used to identify prognostic factors for viral burden rebound, and to assess associations between viral burden rebound and a composite clinical outcome of mortality, intensive care unit admission, and invasive mechanical ventilation initiation, stratified by treatment group. FINDINGS: We included 4592 hospitalised patients with non-oxygen-dependent COVID-19 (1998 [43·5%] women and 2594 [56·5%] men). During the omicron BA.2.2 wave, viral burden rebound occurred in 16 of 242 patients (6·6% [95% CI 4·1-10·5]) receiving nirmatrelvir-ritonavir, 27 of 563 (4·8% [3·3-6·9]) receiving molnupiravir, and 170 of 3787 (4·5% [3·9-5·2]) in the control group. The incidence of viral burden rebound did not differ significantly across the three groups. Immunocompromised status was associated with increased odds of viral burden rebound, regardless of antiviral treatment (nirmatrelvir-ritonavir: odds ratio [OR] 7·37 [95% CI 2·56-21·26], p=0·0002; molnupiravir: 3·05 [1·28-7·25], p=0·012; control: 2·21 [1·50-3·27], p<0·0001). Among patients receiving nirmatrelvir-ritonavir, the odds of viral burden rebound were higher in those aged 18-65 years (vs >65 years; 3·09 [1·00-9·53], p=0·050), those with high comorbidity burden (score >6 on the Charlson Comorbidity Index; 6·02 [2·09-17·38], p=0·0009), and those concomitantly taking corticosteroids (7·51 [1·67-33·82], p=0·0086); whereas the odds were lower in those who were not fully vaccinated (0·16 [0·04-0·67], p=0·012). In patients receiving molnupiravir, those aged 18-65 years (2·68 [1·09-6·58], p=0·032) or on concomitant corticosteroids (3·11 [1·23-7·82], p=0·016) had increased odds of viral burden rebound. We found no association between viral burden rebound and occurrence of the composite clinical outcome from day 5 of follow-up (nirmatrelvir-ritonavir: adjusted OR 1·90 [0·48-7·59], p=0·36; molnupiravir: 1·05 [0·39-2·84], p=0·92; control: 1·27 [0·89-1·80], p=0·18). INTERPRETATION: Viral burden rebound rates are similar between patients with antiviral treatment and those without. Importantly, viral burden rebound was not associated with adverse clinical outcomes. FUNDING: Health and Medical Research Fund, Health Bureau, The Government of the Hong Kong Special Administrative Region, China. TRANSLATION: For the Chinese translation of the abstract see Supplementary Materials section.

Development of multiplex RT-ddPCR assays for detection of SARS-CoV-2 and other common respiratory virus infections.

BACKGROUND: Measures for mitigation of Coronavirus Disease 2019 (COVID-19) were set to reduce the spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). SARS-CoV-2 and other respiratory viruses share similar transmission routes and some common clinical manifestations. Co-circulation of SARS-CoV-2 and other common respiratory viruses is imminent. Therefore, development of multiplex assays for detecting these respiratory viruses is essential for being prepared for future outbreaks of respiratory viruses. METHODS: A panel of three reverse transcription droplet digital PCR (RT-ddPCR) assays were developed to detect 15 different human respiratory viruses. Evaluations of its performance were demonstrated. A total of 100 local and 98 imported COVID-19 cases in Hong Kong were screened for co-infection with other common respiratory viruses. RESULTS: All detected viral targets showed distinct signal clusters using the multiplex RT-ddPCR assays. These assays have a broad range of linearity and good intra-/inter-assay reproducibility for each target. The lower limits of quantification for all targets were ≤46 copies per reaction. Six imported cases of COVID-19 were found to be co-infected with other respiratory viruses, whereas no local case of co-infection was observed. CONCLUSIONS: The multiplex RT-ddPCR assays were demonstrated to be useful for screening of respiratory virus co-infections. The strict preventive measures applied in Hong Kong may be effective in limiting the circulation of other human respiratory viruses. The multiplex assays developed in this study can achieve a robust detection method for clinical and research purposes.

Immunogenicity of a third dose of BNT162b2 to ancestral SARS-CoV-2 & Omicron variant in adults who received two doses of inactivated vaccine.

BACKGROUND: Limited data exist on antibody responses to mixed vaccination strategies involving inactivated COVID-19 vaccines, particularly in the context of emerging variants. METHODS: We conducted an open label trial of a third vaccine dose of an mRNA vaccine (BNT162b2, Fosun Pharma/BioNTech) in adults aged ≥30 years who had previously received two doses of inactivated COVID-19 vaccine. We collected blood samples before administering the third dose and 28 days later, and tested for antibodies to the ancestral virus using a binding assay (ELISA), a surrogate virus neutralization test (sVNT) and a live virus plaque reduction neutralization test (PRNT). We also tested for antibodies against the Omicron variant using live-virus PRNT. RESULTS: In 315 participants, a third dose of BNT162b2 substantially increased antibody titers on each assay. Mean ELISA levels increased from an optical density (OD) of 0.3 to 2.2 (p < 0. 001), and mean sVNT levels increased from an inhibition of 17% to 96% (p < 0.001). In a random subset of 20 participants, the geometric mean PRNT50 titers rose very substantially by 45 fold from Day 0 to Day 28 against the ancestral virus (p < 0.001) and rose by 11 fold against the Omicron variant (p < 0.001). In daily monitoring, post-vaccination reactions subsided within 7 days for over 99% of participants. CONCLUSIONS: A third dose of COVID-19 vaccination with an mRNA vaccine substantially improved antibody levels against the ancestral virus and the Omicron variant with well-tolerated safety profile, in adults who had received two doses of inactivated vaccine 6 months earlier.

Genetic diversity and molecular epidemiology of Middle East Respiratory Syndrome Coronavirus in dromedaries in Ethiopia, 2017-2020.

Middle East respiratory syndrome coronavirus (MERS-CoV) is enzootic in dromedary camels and causes zoonotic infection and disease in humans. Although over 80% of the global population of infected dromedary camels are found in Africa, zoonotic disease had only been reported in the Arabia Peninsula and travel-associated disease has been reported elsewhere. In this study, genetic diversity and molecular epidemiology of MERS-CoV in dromedary camels in Ethiopia were investigated during 2017-2020. Of 1766 nasal swab samples collected, 61 (3.5%) were detected positive for MERS-CoV RNA. Of 484 turbinate swab samples collected, 10 (2.1%) were detected positive for MERS-CoV RNA. Twenty-five whole genome sequences were obtained from these MERS-CoV positive samples. Phylogenetically, these Ethiopian camel-originated MERS-CoV belonged to clade C2, clustering with other East African camel strains. Virus sequences from camel herds clustered geographically while in an abattoir, two distinct phylogenetic clusters of MERS-CoVs were observed in two sequential sampling collections, which indicates the greater genetic diversity of MERS-CoV in abattoirs. In contrast to clade A and B viruses from the Arabian Peninsula, clade C camel-originated MERS-CoV from Ethiopia had various nucleotide insertions and deletions in non-structural gene nsp3, accessory genes ORF3 and ORF5 and structural gene N. This study demonstrates the genetic instability of MERS-CoV in dromedaries in East Africa, which indicates that the virus is still actively adapting to its camel host. The impact of the observed nucleotide insertions and deletions on virus evolution, viral fitness, and zoonotic potential deserves further study.

A rapid, high-throughput, and sensitive PEG-precipitation method for SARS-CoV-2 wastewater surveillance.

The effective application of wastewater surveillance is dependent on testing capacity and sensitivity to obtain high spatial resolution testing results for a timely targeted public health response. To achieve this purpose, the development of rapid, high-throughput, and sensitive virus concentration methods is urgently needed. Various protocols have been developed and implemented in wastewater surveillance networks so far, however, most of them lack the ability to scale up testing capacity or cannot achieve sufficient sensitivity for detecting SARS-CoV-2 RNA at low prevalence. In the present study, using positive raw wastewater in Hong Kong, a PEG precipitation-based three-step centrifugation method was developed, including low-speed centrifugation for large particles removal and the recovery of viral nucleic acid, and medium-speed centrifugation for the concentration of viral nucleic acid. This method could process over 100 samples by two persons per day to reach the process limit of detection (PLoD) of 3286 copies/L wastewater. Additionally, it was found that the testing capacity could be further increased by decreasing incubation and centrifugation time without significantly influencing the method sensitivity. The entire procedure uses ubiquitous reagents and instruments found in most laboratories to obtain robust testing results. This high-throughput, cost-effective, and sensitive tool will promote the establishment of nearly real-time wastewater surveillance networks for valuable public health information.

Risk of within-hotel transmission of SARS-CoV-2 during on-arrival quarantine in Hong Kong: an epidemiological and phylogenomic investigation.

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. However, hotels are not designed with infection control in mind. We aimed to systematically study the potential risk of acquisition of SARS-CoV-2 infection among individuals undergoing hotel quarantine. Methods: We examined data on each laboratory-confirmed COVID-19 case identified in on-arrival quarantine in a hotel in Hong Kong between 1 May 2020 and 31 January 2022. We sequenced the whole genomes of viruses from cases that overlapped with other confirmed cases in terms of the hotel of stay, date of arrival and date of testing positive. By combining multiple sources of evidence, we identify probable and plausible transmission events and calculate the overall risk of transmission. Findings: Among 221 imported cases that overlapped with other cases detected during hotel quarantine with available sequence data, phylogenomic analyses identified five probable and two plausible clusters of within-hotel transmission. Only two of these clusters were recognised at the time. Including other clusters reported in Hong Kong, we estimate that 8-11 per 1000 cases identified in hotel quarantine may be infected by another unlinked case during quarantine, or 2-3 per 100,000 overseas arrivals. Interpretation: We have identified additional undetected occurrences of COVID-19 transmission within hotel quarantine in Hong Kong. Although hotels provide suboptimal infection control as improvised quarantine facilities, the risk of contracting infection whilst in quarantine is low. However, these unlikely events could have high consequences by allowing the virus to spread into immunologically naïve communities. Additional vigilance should be taken in the absence of improved controls to identify such events. If on-arrival quarantine is expected to be used for a long time, quarantine facilities could be purpose-built to minimise the risk of transmission. Funding: Health and Medical Research Fund, Hong Kong.

Priming conditions shape breadth of neutralizing antibody responses to sarbecoviruses.

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 to SARS-CoV-2 infection and vaccination, we here use a multiplex surrogate neutralization assay based on virus spike receptor binding domains of multiple SARS-CoV-2 VoC, as well as related bat and pangolin viruses. We include sera from cohorts of individuals vaccinated with two or three doses of mRNA (BNT162b2) or inactivated SARS-CoV-2 (Coronavac or Sinopharm) vaccines with or without a history of previous SARS-CoV-2 or SARS-CoV-1 infection. SARS-CoV-2 or SARS-CoV-1 infection followed by BNT162b2 vaccine, Omicron BA.2 breakthrough infection following BNT162b2 vaccine or a third dose of BNT162b2 following two doses of BNT162b2 or Coronavac elicit the highest and broadest neutralization across VoCs. For both breadth and magnitude of neutralization across all sarbecoviruses, those infected with SARS-CoV-1 immunized with BNT162b2 outperform all other combinations of infection and/or vaccination. These data may inform vaccine design strategies for generating broadly neutralizing antibodies to SARS-CoV-2 variants or across the sarbecovirus subgenus.

Resurgence of Omicron BA.2 in SARS-CoV-2 infection-naive Hong Kong (preprint)

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 population with low immunity towards natural SARS-CoV-2 infection, high vaccine hesitancy in vulnerable populations, comprehensive disease surveillance and the capacity for stringent public health and social measures. Using genome sequences and epidemiological data from this time, we reconstruct the epidemic trajectory of the BA.2 wave, estimate transmission and incidence rates, and evaluate the effectiveness of policy changes. We identify an increase in the effective reproductive rate (Re) to 9.5 in mid-January 2022, which preceded real-time estimates of transmission (Rt), revealing that BA.2 community transmission was under-ascertained weeks before the epidemic appeared to surge in mid-February 2022. Due to this, public health measures were relaxed in early February (Spring Festival) while Re increased and remained > 1 throughout February. An independent estimation of point prevalence and incidence using phylodynamics also indicates extensive superspreading at this time, which likely contributed to the rapid expansion of the epidemic. This study demonstrates that relying on Rt estimation methods dependent on case reporting can misinform epidemic response planning, sometimes with substantial consequences. There is a need for future research and implementation of improved estimates of epidemic growth in near real-time that combine multiple disparate data sources to better inform outbreak response policy.

Replication of SARS-CoV-2 Omicron BA.2 variant in ex vivo cultures of the human upper and lower respiratory tract.

BACKGROUND: The Omicron BA.2 sublineage has replaced BA.1 worldwide and has comparable levels of immune evasion to BA.1. These observations suggest that the increased transmissibility of BA.2 cannot be explained by the antibody evasion. METHODS: Here, we characterized the replication competence and respiratory tissue tropism of three Omicron variants (BA.1, BA.1.1, BA.2), and compared these with the wild-type virus and Delta variant, in human nasal, bronchial and lung tissues cultured ex vivo. FINDINGS: BA.2 replicated more efficiently in nasal and bronchial tissues at 33°C than wild-type, Delta and BA.1. Both BA.2 and BA.1 had higher replication competence than wild-type and Delta viruses in bronchial tissues at 37°C. BA.1, BA.1.1 and BA.2 replicated at a lower level in lung parenchymal tissues compared to wild-type and Delta viruses. INTERPRETATION: Higher replication competence of Omicron BA.2 in the human upper airway at 33°C than BA.1 may be one of the reasons to explain the current advantage of BA.2 over BA.1. A lower replication level of the tested Omicron variants in human lung tissues is in line with the clinical manifestations of decreased disease severity of patients infected with the Omicron strains compared with other ancestral strains. FUNDING: This work was supported by US National Institute of Allergy and Infectious Diseases and the Theme-Based Research Scheme under University Grants Committee of Hong Kong Special Administrative Region, China.

Homologous and heterologous boosting with CoronaVac and BNT162b2: a randomized trial (the Cobovax study) (preprint)

Background: There are few trials comparing homologous and heterologous third doses of COVID-19 vaccination with inactivated vaccines and mRNA vaccines. Methods: We conducted an open-label randomized trial in adults >=18 years of age who received two doses of inactivated vaccine (CoronaVac) or mRNA vaccine (BNT162b2) >=6 months earlier, randomised in 1:1 ratio to receive a third dose of either vaccine. We compared the reactogenicity, immunogenicity and cell-mediated immune responses, and assessed vaccine efficacy against infections during follow-up. Results: We enrolled 219 adults who previously received two doses of CoronaVac and randomised to CoronaVac ("CC-C", n=101) or BNT162b2 ("CC-B", n=118) third dose; and 232 adults who previously received BNT162b2 and randomised to CoronaVac ("BB-C", n=118) or BNT162b2 ("BB-B", n=114). There were more frequent reports of mild reactions in recipients of third-dose BNT162b2, which generally subsided within 7 days. Third doses significantly increased neutralising PRNT50 antibody titers against ancestral virus and Omicron BA.1 variant in all four study arms, and against Omicron BA.2 in all arms except CC-C, with statistically significant improvements for recipients of a third dose of BNT162b2 over CoronaVac irrespective of prior vaccine type. Boosting of CD4+ T cells only occurred in CoronaVac-primed arms, but we did not identify overall differences between vaccine groups in CD4+ and CD8+ T cell responses. When Omicron BA.2 was circulating, we identified 58 infections with cumulative incidence of 15.3% and 15.4% in the CC-C and CC-B (p=0.93), and 16.7% and 14.0% in the BB-C and BB-B arms, respectively (p=0.56). Conclusions: Similar levels of incidence of infection in each arm suggest all third dose combinations may provide similar degrees of protection against prevalent Omicron BA.2 infection, despite very weak antibody responses to BA.2 in the recipients of a CoronaVac third dose. Further research is warranted to identify appropriate correlates of protection for inactivated COVID-19 vaccines.

Effect of Surface Porosity on SARS-CoV-2 Fomite Infectivity.

Previous reports indicated the low stability of severe actute respiratory syndrome coronovirus 2 (SARS-CoV-2) on various porous surfaces, but the role of porosity was unclear because there was no direct comparison between porous and nonporous solids of the same chemistry. Through comparing pairs of solids with very similar chemistry, we find that porosity is important: porous glass has a much lower infectivity than nonporous glass. However, porosity is not sufficient to lower infectivity; permeability, which is the ability of a liquid to move through a material, is the important parameter. We show this by comparing a pair of porous CuO coatings where the pores are accessible in one case and inaccessible in the other case. When the pores are inaccessible, the infectivity remains similar to that for nonporous solids. Thus, for both glass and CuO, it is the access to porosity that decreases the infectivity of extracted liquid droplets. Having established the importance of permeability, there is the open question of the mechanism of changing the infectivity of SARS-CoV-2. Several hypotheses are possible, such as increasing the difficulty of extracting the virus from the solid, changing the drying time, increasing the surface area of active ingredient, etc. Reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) measurements show that less viral DNA is extracted from a permeable surface, suggesting that the virus becomes trapped in the pores. Finally, we consider the effect of drying. We show that permeability and the water contact angle on the solid have effects on the drying time of a contaminated droplet, which may in turn affect infectivity.

Quantification of SARS-CoV-2 RNA in wastewater treatment plants mirrors the pandemic trend in Hong Kong.

Wastewater-based epidemiology (WBE) for the SARS-CoV-2 virus in wastewater treatment plants (WWTPs) has emerged as a cost-effective and unbiased tool for population-level testing in the community. In the present study, we conducted a 6-month wastewater monitoring campaign from three WWTPs of different flow rates and catchment area characteristics, which serve 28 % (2.1 million people) of Hong Kong residents in total. Wastewater samples collected daily or every other day were concentrated using ultracentrifugation and the SARS-CoV-2 virus RNA in the supernatant was detected using the N1 and E primer sets. The results showed significant correlations between the virus concentration and the number of daily new cases in corresponding catchment areas of the three WWTPs when using 7-day moving average values (Kendall's tau-b value: 0.227-0.608, p < 0.001). SARS-CoV-2 virus concentration was normalized to a fecal indicator using PMMoV concentration and daily flow rates, but the normalization did not enhance the correlation. The key factors contributing to the correlation were also evaluated, including the sampling frequency, testing methods, and smoothing days. This study demonstrates the applicability of wastewater surveillance to monitor overall SARS-CoV-2 pandemic dynamics in a densely populated city like Hong Kong, and provides a large-scale longitudinal reference for the establishment of the long-term sentinel surveillance in WWTPs for WBE of pathogens which could be combined into a city-wide public health observatory.