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1.
Data Science and Management ; 2022.
Article in English | ScienceDirect | ID: covidwho-2004024

ABSTRACT

A novel coronavirus emerged in Wuhan in late 2019 and has caused the COVID-19 pandemic announced by the World Health Organization on March 12, 2020. This study was originally conducted in January 2020 to estimate the potential risk and geographic range of COVID-19 spread within and beyond China at the early stage of the pandemic. A series of connectivity and risk analyses based on domestic and international travel networks were conducted using historical aggregated mobile phone data and air passenger itinerary data. We found that the cordon sanitaire of Wuhan was likely to have occurred during the latter stages of peak population numbers leaving the city, with travellers departing into neighbouring cities and other megacities in China. We estimated that 59,912 air passengers, of which 834 (95% uncertainty interval: 478–1349) had COVID-19 infection, travelled from Wuhan to 382 cities outside of mainland China during the two weeks prior to the city’s lockdown. Most of these destinations were located in Asia, but major hubs in Europe, the US and Australia were also prominent, with a strong correlation seen between the predicted risks of importation and the number of imported cases found. Given the limited understanding of emerging infectious diseases in the very early stages of outbreaks, our approaches and findings in assessing travel patterns and risk of transmission can help guide public health preparedness and intervention design for new COVID-19 waves caused by variants of concern and future pandemics to effectively limit transmission beyond its initial extent.

2.
J Immunol ; 209(2): 280-287, 2022 07 15.
Article in English | MEDLINE | ID: covidwho-1964219

ABSTRACT

Hand, foot, and mouth disease (HFMD), which is mainly caused by coxsackievirus A16 (CVA16) or enterovirus A71 (EV-A71), poses a serious threat to children's health. However, the long-term dynamics of the neutralizing Ab (NAb) response and ideal paired-serum sampling time for serological diagnosis of CVA16-infected HFMD patients were unclear. In this study, 336 CVA16 and 253 EV-A71 PCR-positive HFMD inpatients were enrolled and provided 452 and 495 sera, respectively, for NAb detection. Random-intercept modeling with B-spline was conducted to characterize NAb response kinetics. The NAb titer of CVA16 infection patients was estimated to increase from negative (2.1, 95% confidence interval [CI]: 1.4-3.3) on the day of onset to a peak of 304.8 (95% CI: 233.4-398.3) on day 21 and then remained >64 until 26 mo after onset. However, the NAb response level of EV-A71-infected HFMD patients was much higher than that of CVA16-infected HFMD patients throughout. The geometric mean titer was significantly higher in severe EV-A71-infected patients than in mild patients, with a 2.0-fold (95% CI: 1.4-3.2) increase. When a 4-fold rise in titer was used as the criterion for serological diagnosis of CVA16 and EV-A71 infection, acute-phase serum needs to be collected at 0-5 d, and the corresponding convalescent serum should be respectively collected at 17.4 (95% CI: 9.6-27.4) and 24.4 d (95% CI: 15.3-38.3) after onset, respectively. In conclusion, both CVA16 and EV-A71 infection induce a persistent humoral immune response but have different NAb response levels and paired-serum sampling times for serological diagnosis. Clinical severity can affect the anti-EV-A71 NAb response.


Subject(s)
Enterovirus A, Human , Enterovirus Infections , Enterovirus , Hand, Foot and Mouth Disease , Antibodies, Neutralizing , Child , China/epidemiology , Cohort Studies , Hand, Foot and Mouth Disease/diagnosis , Humans , Infant , Longitudinal Studies
3.
Nat Commun ; 13(1): 3100, 2022 06 03.
Article in English | MEDLINE | ID: covidwho-1931403

ABSTRACT

Determining the duration of immunity induced by booster doses of CoronaVac is crucial for informing recommendations for booster regimens and adjusting immunization strategies. In two single-centre, double-blind, randomised, placebo-controlled phase 2 clinical trials, immunogenicity and safety of four immunization regimens are assessed in adults aged 18 to 59 years and one immunization regimen in adults aged 60 years and older, respectively. Serious adverse events occurring within 6 months after booster doses are recorded as pre-specified secondary endpoints, geometric mean titres (GMTs) of neutralising antibodies one year after the 3-dose schedule immunization and 6 months after the booster doses are assessed as pre-specified exploratory endpoints, GMT fold-decreases in neutralization titres are assessed as post-hoc analyses. Neutralising antibody titres decline approximately 4-fold and 2.5-fold from day 28 to day 180 after third doses in adults aged 18-59 years of age and in adults aged 60 years and older, respectively. No safety concerns are identified during the follow-up period. There are increases in the magnitude and duration of humoral response with homologous booster doses of CoronaVac given 8 months after a primary two-dose immunization series, which could prolong protection and contribute to building our wall of population immunity. Trial number: NCT04352608 and NCT04383574.


Subject(s)
COVID-19 , SARS-CoV-2 , Adolescent , Adult , Aged , Antibodies, Neutralizing , Antibodies, Viral , COVID-19/prevention & control , COVID-19 Vaccines , Follow-Up Studies , Humans , Middle Aged , Young Adult
4.
Lancet Infect Dis ; 22(4): 483-495, 2022 04.
Article in English | MEDLINE | ID: covidwho-1839434

ABSTRACT

BACKGROUND: Large-scale vaccination against COVID-19 is being implemented in many countries with CoronaVac, an inactivated vaccine. We aimed to assess the immune persistence of a two-dose schedule of CoronaVac, and the immunogenicity and safety of a third dose of CoronaVac, in healthy adults aged 18 years and older. METHODS: In the first of two single-centre, double-blind, randomised, placebo-controlled phase 2 clinical trials, adults aged 18-59 years in Jiangsu, China, were initially allocated (1:1) into two vaccination schedule cohorts: a day 0 and day 14 vaccination cohort (cohort 1) and a day 0 and day 28 vaccination cohort (cohort 2); each cohort was randomly assigned (2:2:1) to either a 3 µg dose or 6 µg dose of CoronaVac or a placebo group. Following a protocol amendment on Dec 25, 2020, half of the participants in each cohort were allocated to receive an additional dose 28 days (window period 30 days) after the second dose, and the other half were allocated to receive a third dose 6 months (window period 60 days) after the second dose. In the other phase 2 trial, in Hebei, China, participants aged 60 years and older were assigned sequentially to receive three injections of either 1·5 µg, 3 µg, or 6 µg of vaccine or placebo, administered 28 days apart for the first two doses and 6 months (window period 90 days) apart for doses two and three. The main outcomes of the study were geometric mean titres (GMTs), geometric mean increases (GMIs), and seropositivity of neutralising antibody to SARS-CoV-2 (virus strain SARS-CoV-2/human/CHN/CN1/2020, GenBank accession number MT407649.1), as analysed in the per-protocol population (all participants who completed their assigned third dose). Our reporting is focused on the 3 µg groups, since 3 µg is the licensed formulation. The trials are registered with ClinicalTrials.gov, NCT04352608 and NCT04383574. FINDINGS: 540 (90%) of 600 participants aged 18-59 years were eligible to receive a third dose, of whom 269 (50%) received the primary third dose 2 months after the second dose (cohorts 1a-14d-2m and 2a-28d-2m) and 271 (50%) received a booster dose 8 months after the second dose (cohorts 1b-14d-8m and 2b-28d-8m). In the 3 µg group, neutralising antibody titres induced by the first two doses declined after 6 months to near or below the seropositive cutoff (GMT of 8) for cohort 1b-14d-8m (n=53; GMT 3·9 [95% CI 3·1-5·0]) and for cohort 2b-28d-8m (n=49; 6·8 [5·2-8·8]). When a booster dose was given 8 months after a second dose, GMTs assessed 14 days later increased to 137·9 (95% CI 99·9-190·4) for cohort 1b-14d-8m and 143·1 (110·8-184·7) 28 days later for cohort 2b-28d-8m. GMTs moderately increased following a primary third dose, from 21·8 (95% CI 17·3-27·6) on day 28 after the second dose to 45·8 (35·7-58·9) on day 28 after the third dose in cohort 1a-14d-2m (n=54), and from 38·1 (28·4-51·1) to 49·7 (39·9-61·9) in cohort 2a-28d-2m (n=53). GMTs had decayed to near the positive threshold by 6 months after the third dose: GMT 9·2 (95% CI 7·1-12·0) in cohort 1a-14d-2m and 10·0 (7·3-13·7) in cohort 2a-28d-2m. Similarly, in adults aged 60 years and older who received booster doses (303 [87%] of 350 participants were eligible to receive a third dose), neutralising antibody titres had declined to near or below the seropositive threshold by 6 months after the primary two-dose series. A third dose given 8 months after the second dose significantly increased neutralising antibody concentrations: GMTs increased from 42·9 (95% CI 31·0-59·4) on day 28 after the second dose to 158·5 (96·6-259·2) on day 28 following the third dose (n=29). All adverse reactions reported within 28 days after a third dose were of grade 1 or 2 severity in all vaccination cohorts. There were three serious adverse events (2%) reported by the 150 participants in cohort 1a-14d-2m, four (3%) by 150 participants from cohort 1b-14d-8m, one (1%) by 150 participants in each of cohorts 2a-28d-2m and 2b-28d-8m, and 24 (7%) by 349 participants from cohort 3-28d-8m. INTERPRETATION: A third dose of CoronaVac in adults administered 8 months after a second dose effectively recalled specific immune responses to SARS-CoV-2, which had declined substantially 6 months after two doses of CoronaVac, resulting in a remarkable increase in the concentration of antibodies and indicating that a two-dose schedule generates good immune memory, and a primary third dose given 2 months after the second dose induced slightly higher antibody titres than the primary two doses. FUNDING: National Key Research and Development Program, Beijing Science and Technology Program, and Key Program of the National Natural Science Foundation of China. TRANSLATION: For the Mandarin translation of the abstract see Supplementary Materials section.


Subject(s)
COVID-19 , Adolescent , Adult , Aged , Antibodies, Neutralizing , Antibodies, Viral , COVID-19/prevention & control , COVID-19 Vaccines/adverse effects , Double-Blind Method , Humans , Immunogenicity, Vaccine , Middle Aged , SARS-CoV-2 , Young Adult
5.
Nat Med ; 28(7): 1468-1475, 2022 07.
Article in English | MEDLINE | ID: covidwho-1830085

ABSTRACT

Having adopted a dynamic zero-COVID strategy to respond to SARS-CoV-2 variants with higher transmissibility since August 2021, China is now considering whether, and for how long, this policy can remain in place. The debate has thus shifted towards the identification of mitigation strategies for minimizing disruption to the healthcare system in the case of a nationwide epidemic. To this aim, we developed an age-structured stochastic compartmental susceptible-latent-infectious-removed-susceptible model of SARS-CoV-2 transmission calibrated on the initial growth phase for the 2022 Omicron outbreak in Shanghai, to project COVID-19 burden (that is, number of cases, patients requiring hospitalization and intensive care, and deaths) under hypothetical mitigation scenarios. The model also considers age-specific vaccine coverage data, vaccine efficacy against different clinical endpoints, waning of immunity, different antiviral therapies and nonpharmaceutical interventions. We find that the level of immunity induced by the March 2022 vaccination campaign would be insufficient to prevent an Omicron wave that would result in exceeding critical care capacity with a projected intensive care unit peak demand of 15.6 times the existing capacity and causing approximately 1.55 million deaths. However, we also estimate that protecting vulnerable individuals by ensuring accessibility to vaccines and antiviral therapies, and maintaining implementation of nonpharmaceutical interventions could be sufficient to prevent overwhelming the healthcare system, suggesting that these factors should be points of emphasis in future mitigation policies.


Subject(s)
COVID-19 , SARS-CoV-2 , Antiviral Agents , COVID-19/epidemiology , China/epidemiology , Humans
6.
Emerg Microbes Infect ; 11(1): 1205-1214, 2022 Dec.
Article in English | MEDLINE | ID: covidwho-1774288

ABSTRACT

SARS-CoV-2 infection causes most cases of severe illness and fatality in older age groups. Over 92% of the Chinese population aged ≥12 years has been fully vaccinated against COVID-19 (albeit with vaccines developed against historical lineages). At the end of October 2021, the vaccination programme has been extended to children aged 3-11 years. Here, we aim to assess whether, in this vaccination landscape, the importation of Delta variant infections could shift COVID-19 burden from adults to children. We developed an age-structured susceptible-infectious-removed model of SARS-CoV-2 transmission to simulate epidemics triggered by the importation of Delta variant infections and project the age-specific incidence of SARS-CoV-2 infections, cases, hospitalizations, intensive care unit admissions, and deaths. In the context of the vaccination programme targeting individuals aged ≥12 years, and in the absence of non-pharmaceutical interventions, the importation of Delta variant infections could have led to widespread transmission and substantial disease burden in mainland China, even with vaccination coverage as high as 89% across the eligible age groups. Extending the vaccination roll-out to include children aged 3-11 years (as it was the case since the end of October 2021) is estimated to dramatically decrease the burden of symptomatic infections and hospitalizations within this age group (39% and 68%, respectively, when considering a vaccination coverage of 87%), but would have a low impact on protecting infants. Our findings highlight the importance of including children among the target population and the need to strengthen vaccination efforts by increasing vaccine effectiveness.


Subject(s)
COVID-19 , Vaccines , Adult , Aged , COVID-19/epidemiology , COVID-19/prevention & control , COVID-19 Vaccines , Child , China/epidemiology , Humans , Infant , SARS-CoV-2 , Vaccination
7.
BMC Med ; 20(1): 130, 2022 04 04.
Article in English | MEDLINE | ID: covidwho-1770537

ABSTRACT

BACKGROUND: Hundreds of millions of doses of coronavirus disease 2019 (COVID-19) vaccines have been administered globally, but progress on vaccination varies considerably between countries. We aimed to provide an overall picture of COVID-19 vaccination campaigns, including policy, coverage, and demand of COVID-19 vaccines. METHODS: We conducted a descriptive study of vaccination policy and doses administered data obtained from multiple public sources as of 8 February 2022. We used these data to develop coverage indicators and explore associations of vaccine coverage with socioeconomic and healthcare-related factors. We estimated vaccine demand as numbers of doses required to complete vaccination of countries' target populations according to their national immunization program policies. RESULTS: Messenger RNA and adenovirus vectored vaccines were the most commonly used COVID-19 vaccines in high-income countries, while adenovirus vectored vaccines were the most widely used vaccines worldwide (180 countries). One hundred ninety-two countries have authorized vaccines for the general public, with 40.1% (77/192) targeting individuals over 12 years and 32.3% (62/192) targeting those ≥ 5 years. Forty-eight and 151 countries have started additional-dose and booster-dose vaccination programs, respectively. Globally, there have been 162.1 doses administered per 100 individuals in target populations, with marked inter-region and inter-country heterogeneity. Completed vaccination series coverage ranged from 0.1% to more than 95.0% of country target populations, and numbers of doses administered per 100 individuals in target populations ranged from 0.2 to 308.6. Doses administered per 100 individuals in whole populations correlated with healthcare access and quality index (R2 = 0.59), socio-demographic index (R2 = 0.52), and gross domestic product per capita (R2 = 0.61). At least 6.4 billion doses will be required to complete interim vaccination programs-3.3 billion for primary immunization and 3.1 billion for additional/booster programs. Globally, 0.53 and 0.74 doses per individual in target populations are needed for primary immunization and additional/booster dose programs, respectively. CONCLUSIONS: There is wide country-level disparity and inequity in COVID-19 vaccines rollout, suggesting large gaps in immunity, especially in low-income countries.


Subject(s)
COVID-19 Vaccines , COVID-19 , COVID-19/epidemiology , COVID-19/prevention & control , Humans , Immunization Programs , Policy , Vaccination Coverage
8.
EuropePMC; 2022.
Preprint in English | EuropePMC | ID: ppcovidwho-331890

ABSTRACT

After the adoption of a dynamic zero-COVID strategy in China for nearly two years, whether and for how long this policy can remain in place is unclear. The debate has thus shifted towards the identification of mitigation strategies capable to prevent the disruption of the healthcare system, should a nationwide epidemic caused by the SARS-CoV-2 Omicron variant start to unfold. To this aim, we developed a mathematical model of SARS-CoV-2 transmission tailored to the unique immunization and epidemiological situation of China. We find that the level of immunity induced by the current vaccination campaign would be insufficient to prevent overwhelming the healthcare system and major losses of human lives. Instead, a synergetic strategy would be needed and based on 1) a heterologous booster vaccination campaign, 2) treating 50% of symptomatic cases with an antiviral with an 80% efficacy in preventing severe outcomes, and 3) the adoption of non-pharmaceutical interventions (NPIs) capable of reducing Rt to ≤2. Protecting vulnerable individuals by ensuring accessibility to vaccines and antivirals, and maintaining a certain degree of NPIs should be emphasised in a future mitigation policy, possibly supported by strengthening critical care capacity and the development of highly efficacious vaccines with long-lasting immunity.

9.
Nat Genet ; 54(4): 499-507, 2022 04.
Article in English | MEDLINE | ID: covidwho-1764190

ABSTRACT

Genomic surveillance has shaped our understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. We performed a global landscape analysis on SARS-CoV-2 genomic surveillance and genomic data using a collection of country-specific data. Here, we characterize increasing circulation of the Alpha variant in early 2021, subsequently replaced by the Delta variant around May 2021. SARS-CoV-2 genomic surveillance and sequencing availability varied markedly across countries, with 45 countries performing a high level of routine genomic surveillance and 96 countries with a high availability of SARS-CoV-2 sequencing. We also observed a marked heterogeneity of sequencing percentage, sequencing technologies, turnaround time and completeness of released metadata across regions and income groups. A total of 37% of countries with explicit reporting on variants shared less than half of their sequences of variants of concern (VOCs) in public repositories. Our findings indicate an urgent need to increase timely and full sharing of sequences, the standardization of metadata files and support for countries with limited sequencing and bioinformatics capacity.


Subject(s)
COVID-19 , SARS-CoV-2 , COVID-19/epidemiology , COVID-19/genetics , Genomics , Humans , Information Dissemination , SARS-CoV-2/genetics
10.
Clin Infect Dis ; 74(4): 734-742, 2022 03 01.
Article in English | MEDLINE | ID: covidwho-1707909

ABSTRACT

Recently emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants may pose a threat to immunity. A systematic landscape of neutralizing antibodies against emerging variants is needed. We systematically searched for studies that evaluated neutralizing antibody titers induced by previous infection or vaccination against SARS-CoV-2 variants and collected individual data. We identified 106 studies meeting the eligibility criteria. Lineage B.1.351 (beta), P.1 (gamma) and B.1.617.2 (delta) significantly escaped natural infection-mediated neutralization, with an average of 4.1-fold (95% confidence interval [CI]: 3.6-4.7-fold), 1.8-fold (1.4-2.4-fold), and 3.2-fold (2.4-4.1-fold) reduction in live virus neutralization assay, while neutralizing titers against B.1.1.7 (alpha) decreased slightly (1.4-fold [95% CI: 1.2-1.6-fold]). Serum from vaccinees also led to significant reductions in neutralization of B.1.351 across different platforms, with an average of 7.1-fold (95% CI: 5.5-9.0-fold) for nonreplicating vector platform, 4.1-fold (3.7-4.4-fold) for messenger RNA platform, and 2.5-fold (1.7-2.9-fold) for protein subunit platform. Neutralizing antibody levels induced by messenger RNA vaccines against SARS-CoV-2 variants were similar to, or higher, than that derived from naturally infected individuals.


Subject(s)
Antibodies, Neutralizing/immunology , Antibodies, Viral/immunology , COVID-19 Vaccines/immunology , COVID-19 , SARS-CoV-2 , COVID-19/immunology , COVID-19/prevention & control , Humans , Spike Glycoprotein, Coronavirus/genetics , Vaccination
11.
EuropePMC; 2021.
Preprint in English | EuropePMC | ID: ppcovidwho-325293

ABSTRACT

Introduction: China is facing substantial risks of imported COVID-19 cases and a domestic resurgence in the long run, and COVID-19 vaccination is expected to be the long-lasting solution to end the pandemic. We aim to estimate the size of the target population for COVID-19 vaccination at the provincial level and summarize the current progress of vaccination programs, which could support local governments in the timely determination and adjustment of vaccination policies and promotional measures. Methods: By extracting provincial-stratified data from publicly available sources, we estimated the size of priority target groups for vaccination programs and further characterized the ongoing COVID-19 vaccination program at the provincial level, including the total doses administered, the coverage rate, and the vaccination capacity needed to achieve the target coverage of 70%. Results: The size of the target population shows large differences among provinces, ranging from 3.5 million to 115.2 million. As of June 10, the speed of vaccine roll-out differs remarkably as well, with the highest coverage occurring in Beijing and Shanghai, where 69.8% and 62.3% of the population is fully vaccinated, respectively. However, in 19 of 31 provinces, less than 40% of the population was administered at least one dose, in 9 of which the proportion was even less than 30%. Compared to the routine vaccination capacity before the COVID-19 pandemic, the COVID-19 vaccination capacity has greatly improved. Nevertheless, the current vaccination capacity is far lower than the target of 70% coverage by the end of 2021 or by mid-2022 in approximately 5%-20% of provinces, particularly the Guizhou, Yunnan, Xinjiang, Fujian and Hebei provinces. Conclusions: Large disparities exist in the target population size and vaccination progress across provinces in China. Vaccine coverage is far from meeting the herd immunity threshold, and the vaccination service capacity needs to be further improved.

12.
EuropePMC; 2021.
Preprint in English | EuropePMC | ID: ppcovidwho-324768

ABSTRACT

Strategic prioritization of COVID-19 vaccines is urgently needed, especially in light of the limited supply that is expected to last for most, if not the entire, 2021. Dynamically adapting the allocation strategy to the evolving epidemiological situation could thus be critical during this initial phase of vaccine rollout. We developed a data-driven mechanistic model of SARS-CoV-2 transmission to explore optimal vaccine prioritization strategies in China that aim at reducing COVID-19 burden measured through different metrics. We found that reactively adapting the vaccination program to the epidemiological situation (i.e., allocate vaccine to a target group before reaching full coverage of other groups with initial higher priority) can be highly beneficial as such strategies are capable to simultaneously achieve different objectives (e.g., minimizing the number of deaths and of infections). The highest priority categories are broadly consistent under different hypotheses about vaccine efficacy, differential vaccine efficacy in preventing infection vs. disease, vaccine hesitancy, and SARS-CoV-2 transmissibility. Our findings also suggest that boosting the daily capacities up to 2.5 million courses (0.17% rollout speed) or higher could greatly reduce COVID-19 burden should a new wave start to unfold in China with reproduction number equal to 1.5 or lower. Finally, we estimate that a high vaccine supply in the early phase of the vaccination campaign is key to achieve large gains of strategic prioritizations.

13.
EuropePMC; 2020.
Preprint in English | EuropePMC | ID: ppcovidwho-324469

ABSTRACT

All countries are facing decisions about which groups to prioritise for COVID-19 vaccination after the first vaccine product has been licensed, at which time supply shortages are inevitable. Here we define the key target populations and their size in China for a phased introduction of COVID-19 vaccination with evolving goals, accounting for the risk of illness and transmission. Essential workers (47.2 million) like healthcare workers could be prioritized for vaccination to maintain essential services. Subsequently, older adults, individuals with underlying health conditions and pregnant women (616.0 million) could be targeted to reduce severe COVID-19 outcomes. Then it could be further extended to target adults without underlying health conditions and children (738.7 million) to reduce symptomatic infections and/or to stop virus transmission. The proposed framework could assist Chinese policy-makers in the design of a vaccination program, and could be generalized to inform other national and regional COVID-19 vaccination strategies.

14.
EuropePMC; 2021.
Preprint in English | EuropePMC | ID: ppcovidwho-312588

ABSTRACT

To investigate parenting and children’s emotional and lifestyle responses to the COVID-19 epidemic, we conducted an online survey of random, representative sample of residents with children aged 3–17 years in mid-March, 2020 in China. 1655 parents were surveyed with 80.1% response rate. During the epidemic, half (49%) of children had stress symptoms and 10% had emotional problems;children had higher screen time, less exercise and worse sleep than before. Socially disadvantaged children were more vulnerable to the epidemic. Children whose parents communicated about the epidemic more frequently, who had irritable parents and experienced worse parent-child closeness had higher probabilities of emotional problems, stress symptoms and worse lifestyles. Improve parenting skills and communication quality is necessary during the epidemic.

15.
Lancet Glob Health ; 9(5): e598-e609, 2021 05.
Article in English | MEDLINE | ID: covidwho-1683792

ABSTRACT

BACKGROUND: A rapidly increasing number of serological surveys for antibodies to SARS-CoV-2 have been reported worldwide. We aimed to synthesise, combine, and assess this large corpus of data. METHODS: In this systematic review and meta-analysis, we searched PubMed, Embase, Web of Science, and five preprint servers for articles published in English between Dec 1, 2019, and Dec 22, 2020. Studies evaluating SARS-CoV-2 seroprevalence in humans after the first identified case in the area were included. Studies that only reported serological responses among patients with COVID-19, those using known infection status samples, or any animal experiments were all excluded. All data used for analysis were extracted from included papers. Study quality was assessed using a standardised scale. We estimated age-specific, sex-specific, and race-specific seroprevalence by WHO regions and subpopulations with different levels of exposures, and the ratio of serology-identified infections to virologically confirmed cases. This study is registered with PROSPERO, CRD42020198253. FINDINGS: 16 506 studies were identified in the initial search, 2523 were assessed for eligibility after removal of duplicates and inappropriate titles and abstracts, and 404 serological studies (representing tests in 5 168 360 individuals) were included in the meta-analysis. In the 82 studies of higher quality, close contacts (18·0%, 95% CI 15·7-20·3) and high-risk health-care workers (17·1%, 9·9-24·4) had higher seroprevalence than did low-risk health-care workers (4·2%, 1·5-6·9) and the general population (8·0%, 6·8-9·2). The heterogeneity between included studies was high, with an overall I2 of 99·9% (p<0·0001). Seroprevalence varied greatly across WHO regions, with the lowest seroprevalence of general populations in the Western Pacific region (1·7%, 95% CI 0·0-5·0). The pooled infection-to-case ratio was similar between the region of the Americas (6·9, 95% CI 2·7-17·3) and the European region (8·4, 6·5-10·7), but higher in India (56·5, 28·5-112·0), the only country in the South-East Asia region with data. INTERPRETATION: Antibody-mediated herd immunity is far from being reached in most settings. Estimates of the ratio of serologically detected infections per virologically confirmed cases across WHO regions can help provide insights into the true proportion of the population infected from routine confirmation data. FUNDING: National Science Fund for Distinguished Young Scholars, Key Emergency Project of Shanghai Science and Technology Committee, Program of Shanghai Academic/Technology Research Leader, National Science and Technology Major project of China, the US National Institutes of Health. TRANSLATION: For the Chinese translation of the abstract see Supplementary Materials section.


Subject(s)
COVID-19 Serological Testing , COVID-19/diagnosis , COVID-19/epidemiology , Humans , Seroepidemiologic Studies
16.
BMC Med ; 20(1): 37, 2022 01 31.
Article in English | MEDLINE | ID: covidwho-1662418

ABSTRACT

BACKGROUND: To allow a return to a pre-COVID-19 lifestyle, virtually every country has initiated a vaccination program to mitigate severe disease burden and control transmission. However, it remains to be seen whether herd immunity will be within reach of these programs. METHODS: We developed a compartmental model of SARS-CoV-2 transmission for China, a population with low prior immunity from natural infection. Two vaccination programs were tested and model-based estimates of the immunity level in the population were provided. RESULTS: We found that it is unlikely to reach herd immunity for the Delta variant given the relatively low efficacy of the vaccines used in China throughout 2021 and the lack of prior natural immunity. We estimated that, assuming a vaccine efficacy of 90% against the infection, vaccine-induced herd immunity would require a coverage of 93% or higher of the Chinese population. However, even when vaccine-induced herd immunity is not reached, we estimated that vaccination programs can reduce SARS-CoV-2 infections by 50-62% in case of an all-or-nothing vaccine model and an epidemic starts to unfold on December 1, 2021. CONCLUSIONS: Efforts should be taken to increase population's confidence and willingness to be vaccinated and to develop highly efficacious vaccines for a wide age range.


Subject(s)
COVID-19 , Epidemics , Viral Vaccines , China/epidemiology , Humans , SARS-CoV-2
17.
Nat Commun ; 13(1): 322, 2022 01 14.
Article in English | MEDLINE | ID: covidwho-1625443

ABSTRACT

There are contrasting results concerning the effect of reactive school closure on SARS-CoV-2 transmission. To shed light on this controversy, we developed a data-driven computational model of SARS-CoV-2 transmission. We found that by reactively closing classes based on syndromic surveillance, SARS-CoV-2 infections are reduced by no more than 17.3% (95%CI: 8.0-26.8%), due to the low probability of timely identification of infections in the young population. We thus investigated an alternative triggering mechanism based on repeated screening of students using antigen tests. Depending on the contribution of schools to transmission, this strategy can greatly reduce COVID-19 burden even when school contribution to transmission and immunity in the population is low. Moving forward, the adoption of antigen-based screenings in schools could be instrumental to limit COVID-19 burden while vaccines continue to be rolled out.


Subject(s)
COVID-19/epidemiology , COVID-19/prevention & control , Models, Statistical , Quarantine/organization & administration , SARS-CoV-2/pathogenicity , Schools/organization & administration , COVID-19/diagnosis , COVID-19/transmission , COVID-19 Serological Testing , Computer Simulation , Humans , Italy/epidemiology , Mass Screening/trends , Physical Distancing , SARS-CoV-2/growth & development , SARS-CoV-2/immunology , Schools/legislation & jurisprudence , Students/legislation & jurisprudence
18.
2021.
Preprint in English | Other preprints | ID: ppcovidwho-295683

ABSTRACT

Background Large-scale vaccination is being implemented globally with CoronaVac, an inactivated vaccine against coronavirus disease 2019 (COVID-19). Immunogenicity and safety profiles of homologous two-dose schedules have been published. We report interim results of immune persistence, and the immunogenicity and safety of a third dose of CoronaVac. Methods In this ongoing, placebo-controlled, double-blind phase 2 trial in 18-to-59-year-olds, we randomly assigned subjects, 1:1:1:1, to one of four schedules to receive a third dose, 28 days or 6 months after two two-dose regimens (14-day or 28-day apart): schedule 1 : days 0, 14, 42;schedule 2 : days 0, 14, 194;schedule 3 : days 0, 28, 56;schedule 4 : days 0, 28, 208. For each schedule, participants were randomly assigned to either a medium-dose group (3 μg per 0.5 mL of aluminum hydroxide diluent per dose), a high-dose group (6 μg), or a placebo group (2:2:1). The primary outcome was geometric mean titers (GMTs) of neutralizing antibody to live SARS-CoV-2. Results Overall, 540 participants received a third dose. In the 3 μg group, neutralizing antibody titers induced by the first two doses declined after 6-8 months to below the seropositive cutoff (GMT: 4.1 [95%CI 3.3-5.2] for Schedule 2 and 6.7 [95%CI 5.2-8.6] for Schedule 4 ). When a third dose was given 6-8 months after a second dose, GMTs assessed 14 days later increased to 137.9 [95%CI 99.9-190.4] for Schedule 2 , and 143.1 [95%CI 110.8-184.7] for Schedule 4 , approximately 3-fold above Schedule 1 and Schedule 3 GMTs after third doses. Similar patterns were observed for the 6 μg group. The severity of solicited local and systemic adverse reactions reported within 28 days after the third dose were grade 1 to grade 2 in all vaccination cohorts. None of the fourteen serious adverse events were considered to be related to vaccination. Conclusions A third dose of CoronaVac administered 6 or more months after a second dose effectively recalled specific immune response to SARS-CoV-2, resulting in a remarkable increase in antibody levels, and indicating that a two-dose schedule generates good immune memory. Optimizing the timing of a booster dose should take into account immunogenicity, vaccine efficacy/effectiveness, local epidemic situation, infection risk, and vaccine supply. (Funded by the National Key Research and Development Program, Beijing Science and Technology Program and National Science Fund for Distinguished Young Scholars;ClinicalTrials.gov number, NCT04352608 .)

19.
2021.
Preprint in English | Other preprints | ID: ppcovidwho-295323

ABSTRACT

Background To allow a return to a pre-COVID-19 lifestyle, virtually every country has initiated a vaccination program to mitigate severe disease burden and control transmission. However, it remains to be seen whether herd immunity will be within reach of these programs. Methods We developed a data-driven model of SARS-CoV-2 transmission for China, a population with low prior immunity from natural infection. The model is calibrated considering COVID-19 natural history and the estimated transmissibility of the Delta variant. Three vaccination programs are tested, including the one currently enacted in China and model-based estimates of the herd immunity level are provided. Results We found that it is unlike to reach herd immunity for the Delta variant given the relatively low efficacy of the vaccines used in China throughout 2021, the exclusion of underage individuals from the targeted population, and the lack of prior natural immunity. We estimate that, assuming a vaccine efficacy of 90% against the infection, vaccine-induced herd immunity would require a coverage of 93% or higher of the Chinese population. However, even when vaccine-induced herd immunity is not reached, we estimated that vaccination programs can reduce SARS-CoV-2 infections by 53-58% in case of an epidemic starts to unfold in the fall of 2021. Conclusions Efforts should be taken to increase population’s confidence and willingness to be vaccinated and to guarantee highly efficacious vaccines for a wider age range.

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