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  1. Article ; Online: Modeling COVID-19 dynamics in the sixteen West African countries.

    Honfo, Sewanou H / Taboe, Hemaho B / Glèlè Kakaï, Romain

    Scientific African

    2022  Volume 18, Page(s) e01408

    Abstract: The COVID-19 pandemic is currently causing several damages to the world, especially in the public health sector. Due to identifiability problems in parameters' estimation of complex compartmental models, this study considered a simple deterministic ... ...

    Abstract The COVID-19 pandemic is currently causing several damages to the world, especially in the public health sector. Due to identifiability problems in parameters' estimation of complex compartmental models, this study considered a simple deterministic susceptible-infectious-recovered (SIR)-type model to characterize the first wave and predict the future course of the pandemic in the West African countries. We estimated some specific characteristics of the disease's dynamics, such as its initial conditions, reproduction numbers, true peak and peak of the reported cases, with their corresponding times, final epidemic size and time-varying attack ratio. Our findings revealed a relatively low proportion of susceptible individuals in the region and the different countries (
    Language English
    Publishing date 2022-10-31
    Publishing country Netherlands
    Document type Journal Article
    ISSN 2468-2276
    ISSN (online) 2468-2276
    DOI 10.1016/j.sciaf.2022.e01408
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  2. Article: Unraveling the dynamics of the Omicron and Delta variants of the 2019 coronavirus in the presence of vaccination, mask usage, and antiviral treatment.

    Ngonghala, Calistus N / Taboe, Hemaho B / Safdar, Salman / Gumel, Abba B

    Applied mathematical modelling

    2022  Volume 114, Page(s) 447–465

    Abstract: The effectiveness of control interventions against COVID-19 is threatened by the emergence of SARS-CoV-2 variants of concern. We present a mathematical model for studying the transmission dynamics of two of these variants (Delta and Omicron) in the ... ...

    Abstract The effectiveness of control interventions against COVID-19 is threatened by the emergence of SARS-CoV-2 variants of concern. We present a mathematical model for studying the transmission dynamics of two of these variants (Delta and Omicron) in the United States, in the presence of vaccination, treatment of individuals with clinical symptoms of the disease and the use of face masks. The model is parameterized and cross-validated using observed daily case data for COVID-19 in the United States for the period from November 2021 (when Omicron first emerged) to March 2022. Rigorous qualitative analysis of the model shows that the disease-free equilibrium of the model is locally-asymptotically stable when the control reproduction number of the model (denoted by
    Language English
    Publishing date 2022-09-30
    Publishing country England
    Document type Journal Article
    ZDB-ID 2004151-2
    ISSN 0307-904X
    ISSN 0307-904X
    DOI 10.1016/j.apm.2022.09.017
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  3. Article ; Online: Critical assessment of the impact of vaccine-type and immunity on the burden of COVID-19.

    Taboe, Hemaho B / Asare-Baah, Michael / Iboi, Enahoro A / Ngonghala, Calistus N

    Mathematical biosciences

    2023  Volume 360, Page(s) 108981

    Abstract: The COVID-19 pandemic continues to have a devastating impact on health systems and economies across the globe. Implementing public health measures in tandem with effective vaccination strategies have been instrumental in curtailing the burden of the ... ...

    Abstract The COVID-19 pandemic continues to have a devastating impact on health systems and economies across the globe. Implementing public health measures in tandem with effective vaccination strategies have been instrumental in curtailing the burden of the pandemic. With the three vaccines authorized for use in the U.S. having varying efficacies and waning effects against major COVID-19 strains, understanding the impact of these vaccines on COVID-19 incidence and fatalities is critical. Here, we formulate and use mathematical models to assess the impact of vaccine type, vaccination and booster uptake, and waning of natural and vaccine-induced immunity on the incidence and fatalities of COVID-19 and to predict future trends of the disease in the U.S. when existing control measures are reinforced or relaxed. The results show a 5-fold reduction in the control reproduction number during the initial vaccination period and a 1.8-fold (2-fold) reduction in the control reproduction number during the initial first booster (second booster) uptake period, compared to the respective previous periods. Due to waning of vaccine-induced immunity, vaccinating up to 96% of the U.S. population might be required to attain herd immunity, if booster uptake is low. Additionally, vaccinating and boosting more people from the onset of vaccination and booster uptake, especially with the Pfizer-BioNTech and Moderna vaccines (which confer superior protection than the Johnson & Johnson vaccine) would have led to a significant reduction in COVID-19 cases and deaths in the U.S. Furthermore, adopting natural immunity-boosting measures is important in fighting COVID-19 and transmission rate reduction measures such as mask-use are critical in combating COVID-19. The emergence of a more transmissible COVID-19 variant, or early relaxation of existing control measures can lead to a more devastating wave, especially if transmission rate reduction measures and vaccination are relaxed simultaneously, while chances of containing the pandemic are enhanced if both vaccination and transmission rate reduction measures are reinforced simultaneously. We conclude that maintaining or improving existing control measures, and boosting with mRNA vaccines are critical in curtailing the burden of the pandemic in the U.S.
    MeSH term(s) Humans ; SARS-CoV-2 ; Pandemics/prevention & control ; COVID-19/epidemiology ; COVID-19/prevention & control ; Vaccines
    Chemical Substances Vaccines
    Language English
    Publishing date 2023-02-16
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 1126-5
    ISSN 1879-3134 ; 0025-5564
    ISSN (online) 1879-3134
    ISSN 0025-5564
    DOI 10.1016/j.mbs.2023.108981
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    Zs.A 1534: Show issues Location:
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    Jg. 1995 - 2021: Lesesall (1.OG)
    ab Jg. 2022: Lesesaal (EG)

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  4. Article ; Online: The impact of age structure and vaccine prioritization on COVID-19 in West Africa.

    Taboe, Hemaho B / Asare-Baah, Michael / Yesmin, Afsana / Ngonghala, Calistus N

    Infectious Disease Modelling

    2022  Volume 7, Issue 4, Page(s) 709–727

    Abstract: The ongoing COVID-19 pandemic has been a major global health challenge since its emergence in 2019. Contrary to early predictions that sub-Saharan Africa (SSA) would bear a disproportionate share of the burden of COVID-19 due to the region's ... ...

    Abstract The ongoing COVID-19 pandemic has been a major global health challenge since its emergence in 2019. Contrary to early predictions that sub-Saharan Africa (SSA) would bear a disproportionate share of the burden of COVID-19 due to the region's vulnerability to other infectious diseases, weak healthcare systems, and socioeconomic conditions, the pandemic's effects in SSA have been very mild in comparison to other regions. Interestingly, the number of cases, hospitalizations, and disease-induced deaths in SSA remain low, despite the loose implementation of non-pharmaceutical interventions (NPIs) and the low availability and administration of vaccines. Possible explanations for this low burden include epidemiological disparities, under-reporting (due to limited testing), climatic factors, population structure, and government policy initiatives. In this study, we formulate a model framework consisting of a basic model (in which only susceptible individuals are vaccinated), a vaccine-structured model, and a hybrid vaccine-age-structured model to assess the dynamics of COVID-19 in West Africa (WA). The framework is trained with a portion of the confirmed daily COVID-19 case data for 16 West African countries, validated with the remaining portion of the data, and used to (i) assess the effect of age structure on the incidence of COVID-19 in WA, (ii) evaluate the impact of vaccination and vaccine prioritization based on age brackets on the burden of COVID-19 in the sub-region, and (iii) explore plausible reasons for the low burden of COVID-19 in WA compared to other parts of the world. Calibration of the model parameters and global sensitivity analysis show that asymptomatic youths are the primary drivers of the pandemic in WA. Also, the basic and control reproduction numbers of the hybrid vaccine-age-structured model are smaller than those of the other two models indicating that the disease burden is overestimated in the models which do not account for age-structure. This result is confirmed through the vaccine-derived herd immunity thresholds. In particular, a comprehensive analysis of the basic (vaccine-structured) model reveals that if 84%(73%) of the West African populace is fully immunized with the vaccines authorized for use in WA, vaccine-derived herd immunity can be achieved. This herd immunity threshold is lower (68%) for the hybrid model. Also, all three thresholds are lower (60% for the basic model, 51% for the vaccine-structured model, and 48% for the hybrid model) if vaccines of higher efficacies (e.g., the Pfizer or Moderna vaccine) are prioritized, and higher if vaccines of lower efficacy are prioritized. Simulations of the models show that controlling the COVID-19 pandemic in WA (by reducing transmission) requires a proactive approach, including prioritizing vaccination of more youths or vaccination of more youths and elderly simultaneously. Moreover, complementing vaccination with a higher level of mask compliance will improve the prospects of containing the pandemic. Additionally, simulations of the model predict another COVID-19 wave (with a smaller peak size compared to the Omicron wave) by mid-July 2022. Furthermore, the emergence of a more transmissible variant or easing the existing measures that are effective in reducing transmission will result in more devastating COVID-19 waves in the future. To conclude, accounting for age-structure is important in understanding why the burden of COVID-19 has been low in WA and sustaining the current vaccination level, complemented with the WHO recommended NPIs is critical in curbing the spread of the disease in WA.
    Language English
    Publishing date 2022-09-08
    Publishing country China
    Document type Journal Article
    ZDB-ID 3015225-2
    ISSN 2468-0427 ; 2468-2152
    ISSN (online) 2468-0427
    ISSN 2468-2152
    DOI 10.1016/j.idm.2022.08.006
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  5. Article ; Online: Dynamics of the Delta and Omicron variants of SARS-CoV-2 in the United States: the battle of supremacy in the presence of vaccination, mask usage and antiviral treatment

    Ngonghala, Calistus N / Taboe, Hemaho B / Gumel, Abba B

    medRxiv

    Abstract: Multiple safe and effective vaccines and antiviral drugs have been approved or authorized for use against the COVID-19 pandemic in the United States. The effectiveness of these and other intervention measures is threatened by the emergence of numerous ... ...

    Abstract Multiple safe and effective vaccines and antiviral drugs have been approved or authorized for use against the COVID-19 pandemic in the United States. The effectiveness of these and other intervention measures is threatened by the emergence of numerous SARS-CoV-2 variants of concern. We present a model for studying the transmission dynamics of two of these variants (Delta and Omicron) in the presence of vaccination, treatment of individuals with clinical symptoms of the disease and the use of face masks in the community. The model was fitted using daily case data for the COVID-19 pandemic in the United States corresponding to the period starting from when Omicron first emerged (end of November 2021) to date. It is shown, based on simulating the model with the current COVID-19 data, that the reproduction number of the Delta variant (denoted by Rvd) is much smaller than one (Rvd = 0.28), while that of Omicron (denoted by Rvo) is approximately equal to unity (Rvo = 0.96). This shows that the Delta variant has essentially died out, and that Omicron is currently the predominant variant of concern in the United States. Furthermore, if the current baseline levels of the control measures being implemented in the United States are maintained, the Omicron variant will also be on a rapid decline (towards elimination). The analysis and simulations of the calibrated model show that vaccine-derived immunity can be achieved in the United States if at least 68% of the population is fully-vaccinated with either the Pfizer or Moderna vaccine. It is shown that the COVID-19 pandemic can be eliminated in the United States by June of 2022 if the current baseline level of the proportion of individuals that is fully-vaccinated is increased by about 20%. The threshold vaccination coverage needed to achieve the vaccine-derived herd immunity decreases if the vaccination program is combined with a face mask use strategy, particularly one that emphasizes the use of moderate to high quality masks (e.g., surgical or N95 masks). Greater reduction in disease burden (in comparison to the baseline scenario) are recorded if the very high quality N95 masks are prioritized in the community, followed by the moderately-effective surgical masks and then the lowly-effective cloth masks. We also showed that having high percentage of the populace wearing the moderately-effective surgical mask is more beneficial to the community than having low percentage of the populace wearing the highly-effective N95 masks (this result does not hold for the case when cloth masks compliance is compared with that of N95 masks). However, if a certain (fixed) percentage is to give up masking, our study showed that it is more beneficial if they give up wearing surgical masks and not N95 masks (in other words, in a head-to-head comparison, N95 is always superior than surgical mask). This study showed that waning natural and vaccine-derived immunity (if considered individually) offer marginal impact on disease burden, except for the case when they wane at a much faster rate (e.g., within three months), in comparison to the baseline (estimated to be within 9 months to a year). Greater reduction or increase in disease burden is recorded if both the vaccine-derived and natural immunity wane at the same time (rather than the case when we considered only one of them varying, while the other is at baseline). For instance, if both vaccine-derived and natural immunity wane within three months, a 14% increase in the peak daily cases will be recorded, in comparison to the baseline. For this case, where immunity wanes within three months, our study predicts another (but milder) Omicron wave in the United States that peaks around July 2022 (with the peak 72% lower than the original Omicron peak). Under this (fast waning) scenario, our study suggests that a fourth dose of the two mRNA vaccines would need to be approved in the United States to aid and accelerate the prospect of SARS-CoV-2 elimination in 2022. It is shown that while the treatment of symptomatic individuals has marginal effect in reducing daily cases of SARS-CoV-2, in comparison to the baseline, it has significant impact in reducing daily hospitalizations. It is further shown that, while treatment significantly reduces hospitalization, the prospects of COVID-19 elimination in the United States is more significantly enhanced if investments in control resources are focused on mask usage and vaccination rather than on treatment.
    Keywords covid19
    Language English
    Publishing date 2022-02-24
    Publisher Cold Spring Harbor Laboratory Press
    Document type Article ; Online
    DOI 10.1101/2022.02.23.22271394
    Database COVID19

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  6. Article ; Online: Predicting COVID-19 spread in the face of control measures in West Africa.

    Taboe, Hémaho B / Salako, Kolawolé V / Tison, James M / Ngonghala, Calistus N / Glèlè Kakaï, Romain

    Mathematical biosciences

    2020  Volume 328, Page(s) 108431

    Abstract: The novel coronavirus (COVID-19) pandemic is causing devastating demographic, social, and economic damage globally. Understanding current patterns of the pandemic spread and forecasting its long-term trajectory is essential in guiding policies aimed at ... ...

    Abstract The novel coronavirus (COVID-19) pandemic is causing devastating demographic, social, and economic damage globally. Understanding current patterns of the pandemic spread and forecasting its long-term trajectory is essential in guiding policies aimed at curtailing the pandemic. This is particularly important in regions with weak economies and fragile health care systems such as West Africa. We formulate and use a deterministic compartmental model to (i) assess the current patterns of COVID-19 spread in West Africa, (ii) evaluate the impact of currently implemented control measures, and (iii) predict the future course of the pandemic with and without currently implemented and additional control measures in West Africa. An analytical expression for the threshold level of control measures (involving a reduction in the effective contact rate) required to curtail the pandemic is computed. Considering currently applied health control measures, numerical simulations of the model using baseline parameter values estimated from West African COVID-19 data project a 67% reduction in the daily number of cases when the epidemic attains its peak. More reduction in the number of cases will be achieved if additional public health control measures that result in a reduction in the effective contact rate are implemented. We found out that disease elimination is difficult when more asymptomatic individuals contribute in transmission or are not identified and isolated in a timely manner. However, maintaining a baseline level of asymptomatic isolation and a low transmission rate will lead to a significant reduction in the number of daily cases when the pandemic peaks. For example, at the baseline level of asymptomatic isolation, at least a 46% reduction in the transmission rate is required for disease elimination. Additionally, disease elimination is possible if asymptomatic individuals are identified and isolated within 5 days (after the incubation period). Combining two or more measures is better for disease control, e.g., if asymptomatic cases are contact traced or identified and isolated in less than 8 days, only about 29% reduction in the disease transmission rate is required for disease elimination. Furthermore, we showed that the currently implemented measures triggered a 33% reduction in the time-dependent effective reproduction number between February 28 and June 26, 2020. We conclude that curtailing the COVID-19 pandemic burden significantly in West Africa requires more control measures than those that have already been implemented, as well as more mass testing and contact tracing in order to identify and isolate asymptomatic individuals early.
    MeSH term(s) Africa, Western/epidemiology ; Basic Reproduction Number ; Betacoronavirus ; COVID-19 ; Communicable Disease Control/methods ; Communicable Disease Control/statistics & numerical data ; Computer Simulation ; Contact Tracing ; Coronavirus Infections/epidemiology ; Coronavirus Infections/prevention & control ; Coronavirus Infections/transmission ; Forecasting/methods ; Humans ; Mathematical Concepts ; Models, Biological ; Models, Statistical ; Pandemics/prevention & control ; Pneumonia, Viral/epidemiology ; Pneumonia, Viral/prevention & control ; Pneumonia, Viral/transmission ; Public Health ; SARS-CoV-2
    Keywords covid19
    Language English
    Publishing date 2020-07-29
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1126-5
    ISSN 1879-3134 ; 0025-5564
    ISSN (online) 1879-3134
    ISSN 0025-5564
    DOI 10.1016/j.mbs.2020.108431
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    Jg. 1995 - 2021: Lesesall (1.OG)
    ab Jg. 2022: Lesesaal (EG)

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  7. Article ; Online: Quantifying the impact of vaccines and booster doses on COVID-19 in the U.S.

    Taboe, Hemaho B. / Asare-Baah, Michael / Iboi, Enahoro A. / Ngonghala, Calistus N.

    medRxiv

    Abstract: The 2019 coronavirus (COVID-19) pandemic continues to have a devastating impact on health systems and economies across the globe, with the United States (U.S.) among the worse impacted nations. Implementing public health measures in tandem with effective ...

    Abstract The 2019 coronavirus (COVID-19) pandemic continues to have a devastating impact on health systems and economies across the globe, with the United States (U.S.) among the worse impacted nations. Implementing public health measures in tandem with effective vaccination strategies is instrumental in halting the transmission of the virus and curtailing the burden of the pandemic. Currently, the U.S. Food and Drug Administration has authorized the use of the PfizerBioNTech, Moderna, and the Johnson & Johnson vaccines to prevent COVID-19 in the U.S. However, these vaccines have varying efficacies (≈ 95% for the Pfizer-BioNTech and Moderna vaccines and ≈ 70% for the Johnson & Johnson vaccine) and waning effects against major COVID-19 strains, hence, understanding their impact on the incidence of COVID-19 in the U.S. is critical. Here, we formulate and use mathematical models 1) to investigate the impact of each vaccine type and booster doses (single/double) on the incidence of COVID-19 in the U.S., and 2) to predict future trends of the disease in the U.S., if existing control measures are reinforced or relaxed. The models are fitted to part of the new daily confirmed case data from the U.S., and validated using the remaining part of the daily data, as well as the full cumulative case data. The fitting and numerical simulations of the models show a 44% (71%) reduction in the reproduction number (number of new daily confirmed cases) at the peak during the wave in which vaccination peaked compared to the preceding wave. Additionally, the estimated disease transmission rate is ≈ 3 times higher for the Omicron variant. Simulations of the model show that in the absence of booster shots, the time to elimination of community transmission in the U.S. would have increased by at least two months compared to the baseline case. However, had more people (i.e., 70% of the fully vaccinated population) been boosted by mid-August 2021, ≈ 78% of the daily incidence could have been prevented as at the time the first case of Omicron was reported in the U.S. Our findings suggest that booster shots with the Pfizer-BioNTech or Moderna vaccines conferred superior protection than those with the Johnson & Johnson vaccine. Furthermore, the simulations show that the baseline value of the new daily cases at the peak of the Omicron variant in January 2022 would have dropped significantly (by ≈ 20%) if a fourth dose of the Pfizer-BioNTech or Moderna vaccine was administered at the start of the Omicron wave. Specifically, three million cumulative cases in the U.S. could have been averted between late November 2021 and March 2022. The study proves that early administration of vaccines and booster doses could have significantly reduced the surge in cases and the observed peak size. In particular, we showed that, while late boosting will result in an increase in the number of cases (compared to the baseline value), early boosting will lead to a decrease in the number of cases. Additionally, we showed that a second booster dose using the Pfizer-BioNTech or Moderna vaccine is important in curtailing the burden of the pandemic in the U.S. Particularly if this second dose is administered soon after the first dose. Furthermore, the study shows that early relaxation of existing control measures can lead to a more devastating wave, especially if both vaccination and transmission rate reducing measures such as mask-use are relaxed simultaneous. Keywords: COVID-19 pandemic; Vaccine efficacy; Booster doses; Delta and Omicron variants; Waning vaccine-derived and natural immunity; Infectious disease models.
    Keywords covid19
    Language English
    Publishing date 2022-07-07
    Publisher Cold Spring Harbor Laboratory Press
    Document type Article ; Online
    DOI 10.1101/2022.07.06.22277303
    Database COVID19

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  8. Article ; Online: Predicting COVID-19 spread in the face of control measures in West Africa

    Taboe, Hémaho B. / Salako, Kolawolé V. / Tison, James M. / Ngonghala, Calistus N. / Glèlè Kakaï, Romain

    Mathematical Biosciences

    2020  Volume 328, Page(s) 108431

    Keywords General Biochemistry, Genetics and Molecular Biology ; Modelling and Simulation ; Statistics and Probability ; General Immunology and Microbiology ; Applied Mathematics ; General Agricultural and Biological Sciences ; General Medicine ; covid19
    Language English
    Publisher Elsevier BV
    Publishing country us
    Document type Article ; Online
    ZDB-ID 1126-5
    ISSN 1879-3134 ; 0025-5564
    ISSN (online) 1879-3134
    ISSN 0025-5564
    DOI 10.1016/j.mbs.2020.108431
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    Jg. 1995 - 2021: Lesesall (1.OG)
    ab Jg. 2022: Lesesaal (EG)

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  9. Article: Predicting COVID-19 spread in the face of control measures in West Africa

    Taboe, Hémaho B / Salako, Kolawolé V / Tison, James M / Ngonghala, Calistus N / Glèlè Kakaï, Romain

    Math Biosci

    Abstract: The novel coronavirus (COVID-19) pandemic is causing devastating demographic, social, and economic damage globally. Understanding current patterns of the pandemic spread and forecasting its long-term trajectory is essential in guiding policies aimed at ... ...

    Abstract The novel coronavirus (COVID-19) pandemic is causing devastating demographic, social, and economic damage globally. Understanding current patterns of the pandemic spread and forecasting its long-term trajectory is essential in guiding policies aimed at curtailing the pandemic. This is particularly important in regions with weak economies and fragile health care systems such as West Africa. We formulate and use a deterministic compartmental model to (i) assess the current patterns of COVID-19 spread in West Africa, (ii) evaluate the impact of currently implemented control measures, and (iii) predict the future course of the pandemic with and without currently implemented and additional control measures in West Africa. An analytical expression for the threshold level of control measures (involving a reduction in the effective contact rate) required to curtail the pandemic is computed. Considering currently applied health control measures, numerical simulations of the model using baseline parameter values estimated from West African COVID-19 data project a 67% reduction in the daily number of cases when the epidemic attains its peak. More reduction in the number of cases will be achieved if additional public health control measures that result in a reduction in the effective contact rate are implemented. We found out that disease elimination is difficult when more asymptomatic individuals contribute in transmission or are not identified and isolated in a timely manner. However, maintaining a baseline level of asymptomatic isolation and a low transmission rate will lead to a significant reduction in the number of daily cases when the pandemic peaks. For example, at the baseline level of asymptomatic isolation, at least a 46% reduction in the transmission rate is required for disease elimination. Additionally, disease elimination is possible if asymptomatic individuals are identified and isolated within 5 days (after the incubation period). Combining two or more measures is better for disease control, e.g., if asymptomatic cases are contact traced or identified and isolated in less than 8 days, only about 29% reduction in the disease transmission rate is required for disease elimination. Furthermore, we showed that the currently implemented measures triggered a 33% reduction in the time-dependent effective reproduction number between February 28 and June 26, 2020. We conclude that curtailing the COVID-19 pandemic burden significantly in West Africa requires more control measures than those that have already been implemented, as well as more mass testing and contact tracing in order to identify and isolate asymptomatic individuals early.
    Keywords covid19
    Publisher WHO
    Document type Article
    Note WHO #Covidence: #684665
    Database COVID19

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