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Article ; Online: Evolutionary dynamics in an SI epidemic model with phenotype-structured susceptible compartment.

Lorenzi, Tommaso / Pugliese, Andrea / Sensi, Mattia / Zardini, Agnese

2021 Volume 83, Issue 6-7, Page(s) 72

Abstract: We present an SI epidemic model whereby a continuous structuring variable captures variability in proliferative potential and resistance to infection among susceptible individuals. The occurrence of heritable, spontaneous changes in these phenotypic ... ...

Abstract	We present an SI epidemic model whereby a continuous structuring variable captures variability in proliferative potential and resistance to infection among susceptible individuals. The occurrence of heritable, spontaneous changes in these phenotypic characteristics and the presence of a fitness trade-off between resistance to infection and proliferative potential are explicitly incorporated into the model. The model comprises an ordinary differential equation for the number of infected individuals that is coupled with a partial integrodifferential equation for the population density function of susceptible individuals through an integral term. The expression for the basic reproduction number [Formula: see text] is derived, the disease-free equilibrium and endemic equilibrium of the model are characterised and a threshold theorem involving [Formula: see text] is proved. Analytical results are integrated with the results of numerical simulations of a calibrated version of the model based on the results of artificial selection experiments in a host-parasite system. The results of our mathematical study disentangle the impact of different evolutionary parameters on the spread of infectious diseases and the consequent phenotypic adaption of susceptible individuals. In particular, these results provide a theoretical basis for the observation that infectious diseases exerting stronger selective pressures on susceptible individuals and being characterised by higher infection rates are more likely to spread. Moreover, our results indicate that heritable, spontaneous phenotypic changes in proliferative potential and resistance to infection can either promote or prevent the spread of infectious diseases depending on the strength of selection acting on susceptible individuals prior to infection. Finally, we demonstrate that, when an endemic equilibrium is established, higher levels of resistance to infection and lower degrees of phenotypic heterogeneity among susceptible individuals are to be expected in the presence of infections which are characterised by lower rates of death and exert stronger selective pressures.
MeSH term(s)	Basic Reproduction Number ; Epidemics ; Humans ; Phenotype ; Population Density
Language	English
Publishing date	2021-12-06
Publishing country	Germany
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	187101-8
ISSN	1432-1416 ; 0303-6812
ISSN (online)	1432-1416
ISSN	0303-6812
DOI	10.1007/s00285-021-01703-1
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Article ; Online: Priority age targets for COVID-19 vaccination in Ethiopia under limited vaccine supply.

Galli, Margherita / Zardini, Agnese / Gamshie, Worku Nigussa / Santini, Stefano / Tsegaye, Ademe / Trentini, Filippo / Marziano, Valentina / Guzzetta, Giorgio / Manica, Mattia / d'Andrea, Valeria / Putoto, Giovanni / Manenti, Fabio / Ajelli, Marco / Poletti, Piero / Merler, Stefano

Scientific reports

2023 Volume 13, Issue 1, Page(s) 5586

Abstract: The worldwide inequitable access to vaccination claims for a re-assessment of policies that could minimize the COVID-19 burden in low-income countries. Nine months after the launch of the national vaccination program in March 2021, only 3.4% of the ... ...

Abstract	The worldwide inequitable access to vaccination claims for a re-assessment of policies that could minimize the COVID-19 burden in low-income countries. Nine months after the launch of the national vaccination program in March 2021, only 3.4% of the Ethiopian population received two doses of COVID-19 vaccine. We used a SARS-CoV-2 transmission model to estimate the level of immunity accrued before the launch of vaccination in the Southwest Shewa Zone (SWSZ) and to evaluate the impact of alternative age priority vaccination targets in a context of limited vaccine supply. The model was informed with available epidemiological evidence and detailed contact data collected across different geographical settings (urban, rural, or remote). We found that, during the first year of the pandemic, the mean proportion of critical cases occurred in SWSZ attributable to infectors under 30 years of age would range between 24.9 and 48.0%, depending on the geographical setting. During the Delta wave, the contribution of this age group in causing critical cases was estimated to increase on average to 66.7-70.6%. Our findings suggest that, when considering the vaccine product available at the time (ChAdOx1 nCoV-19; 65% efficacy against infection after 2 doses), prioritizing the elderly for vaccination remained the best strategy to minimize the disease burden caused by Delta, irrespectively of the number of available doses. Vaccination of all individuals aged ≥ 50 years would have averted 40 (95%PI: 18-60), 90 (95%PI: 61-111), and 62 (95%PI: 21-108) critical cases per 100,000 residents in urban, rural, and remote areas, respectively. Vaccination of all individuals aged ≥ 30 years would have averted an average of 86-152 critical cases per 100,000 individuals, depending on the setting considered. Despite infections among children and young adults likely caused 70% of critical cases during the Delta wave in SWSZ, most vulnerable ages should remain a key priority target for vaccination against COVID-19.
MeSH term(s)	Child ; Aged ; Young Adult ; Humans ; Adult ; COVID-19 Vaccines ; Ethiopia ; ChAdOx1 nCoV-19 ; COVID-19 ; SARS-CoV-2 ; Vaccines ; Vaccination
Chemical Substances	COVID-19 Vaccines ; ChAdOx1 nCoV-19 (B5S3K2V0G8) ; Vaccines
Language	English
Publishing date	2023-04-05
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2615211-3
ISSN	2045-2322 ; 2045-2322
ISSN (online)	2045-2322
ISSN	2045-2322
DOI	10.1038/s41598-023-32501-y
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Article ; Online: Spatiotemporal distribution of vector mosquito species and areas at risk for arbovirus transmission in Maricopa County, Arizona.

Wilke, André B B / Damian, Dan / Litvinova, Maria / Byrne, Thomas / Zardini, Agnese / Poletti, Piero / Merler, Stefano / Mutebi, John-Paul / Townsend, John / Ajelli, Marco

Acta tropica

2023 Volume 240, Page(s) 106833

Abstract: Mosquito-borne diseases are a major global public health concern and mosquito surveillance systems are essential for the implementation of effective mosquito control strategies. The objective of our study is to determine the spatiotemporal distribution ... ...

Abstract	Mosquito-borne diseases are a major global public health concern and mosquito surveillance systems are essential for the implementation of effective mosquito control strategies. The objective of our study is to determine the spatiotemporal distribution of vector mosquito species in Maricopa County, AZ from 2011 to 2021, and to identify the hotspot areas for West Nile virus (WNV) and St. Louis Encephalitis virus (SLEV) transmission in 2021. The Maricopa County Mosquito Control surveillance system utilizes BG-Sentinel and EVS-CDC traps throughout the entire urban and suburban areas of the county. We estimated specific mosquito species relative abundance per unit area using the Kernel density estimator in ArcGIS 10.2. We calculated the distance between all traps in the surveillance system and created a 4 km buffer radius around each trap to calculate the extent to which each trap deviated from the mean number of Culex quinquefasciatus and Culex tarsalis collected in 2021. Our results show that vector mosquito species are widely distributed and abundant in the urban areas of Maricopa County. A total of 691,170Cx. quinquefasciatus, 542,733 Cx. tarsalis, and 292,305 Aedes aegypti were collected from 2011 to 2022. The relative abundance of Ae. aegypti was highly seasonal peaking in the third and fourth quarters of the year. Culex quinquefasciatus, on the other hand, was abundant throughout the year with several regions consistently yielding high numbers of mosquitoes. Culex tarsalis was abundant but it only reached high numbers in well-defined areas near irrigated landscapes. We also detected high levels of heterogeneity in the risk of WNV and SLEV transmission to humans disregarding traps geographical proximity. The well-defined species-specific spatiotemporal and geographical patterns found in this study can be used to inform vector control operations.
MeSH term(s)	Animals ; Humans ; Arboviruses ; Mosquito Vectors ; Arizona ; West Nile virus ; Geography ; Culex ; Aedes
Language	English
Publishing date	2023-02-01
Publishing country	Netherlands
Document type	Journal Article
ZDB-ID	210415-5
ISSN	1873-6254 ; 0001-706X
ISSN (online)	1873-6254
ISSN	0001-706X
DOI	10.1016/j.actatropica.2023.106833
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Article ; Online: Evaluation of Waning of SARS-CoV-2 Vaccine-Induced Immunity: A Systematic Review and Meta-analysis.

Menegale, Francesco / Manica, Mattia / Zardini, Agnese / Guzzetta, Giorgio / Marziano, Valentina / d'Andrea, Valeria / Trentini, Filippo / Ajelli, Marco / Poletti, Piero / Merler, Stefano

JAMA network open

2023 Volume 6, Issue 5, Page(s) e2310650

Abstract: Importance: Estimates of the rate of waning of vaccine effectiveness (VE) against COVID-19 are key to assess population levels of protection and future needs for booster doses to face the resurgence of epidemic waves.: Objective: To quantify the ... ...

Abstract	Importance: Estimates of the rate of waning of vaccine effectiveness (VE) against COVID-19 are key to assess population levels of protection and future needs for booster doses to face the resurgence of epidemic waves. Objective: To quantify the progressive waning of VE associated with the Delta and Omicron variants of SARS-CoV-2 by number of received doses. Data sources: PubMed and Web of Science were searched from the databases' inception to October 19, 2022, as well as reference lists of eligible articles. Preprints were included. Study selection: Selected studies for this systematic review and meta-analysis were original articles reporting estimates of VE over time against laboratory-confirmed SARS-CoV-2 infection and symptomatic disease. Data extraction and synthesis: Estimates of VE at different time points from vaccination were retrieved from original studies. A secondary data analysis was performed to project VE at any time from last dose administration, improving the comparability across different studies and between the 2 considered variants. Pooled estimates were obtained from random-effects meta-analysis. Main outcomes and measures: Outcomes were VE against laboratory-confirmed Omicron or Delta infection and symptomatic disease and half-life and waning rate associated with vaccine-induced protection. Results: A total of 799 original articles and 149 reviews published in peer-reviewed journals and 35 preprints were identified. Of these, 40 studies were included in the analysis. Pooled estimates of VE of a primary vaccination cycle against laboratory-confirmed Omicron infection and symptomatic disease were both lower than 20% at 6 months from last dose administration. Booster doses restored VE to levels comparable to those acquired soon after the administration of the primary cycle. However, 9 months after booster administration, VE against Omicron was lower than 30% against laboratory-confirmed infection and symptomatic disease. The half-life of VE against symptomatic infection was estimated to be 87 days (95% CI, 67-129 days) for Omicron compared with 316 days (95% CI, 240-470 days) for Delta. Similar waning rates of VE were found for different age segments of the population. Conclusions and relevance: These findings suggest that the effectiveness of COVID-19 vaccines against laboratory-confirmed Omicron or Delta infection and symptomatic disease rapidly wanes over time after the primary vaccination cycle and booster dose. These results can inform the design of appropriate targets and timing for future vaccination programs.
MeSH term(s)	Humans ; COVID-19 Vaccines ; COVID-19/epidemiology ; COVID-19/prevention & control ; SARS-CoV-2 ; Hepatitis D
Chemical Substances	COVID-19 Vaccines
Language	English
Publishing date	2023-05-01
Publishing country	United States
Document type	Meta-Analysis ; Systematic Review ; Journal Article ; Research Support, U.S. Gov't, P.H.S. ; Research Support, Non-U.S. Gov't
ISSN	2574-3805
ISSN (online)	2574-3805
DOI	10.1001/jamanetworkopen.2023.10650
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Article ; Online: Spatiotemporal distribution of vector mosquito species and areas at risk for arbovirus transmission in Maricopa County, Arizona

Wilke, André B.B. / Damian, Dan / Litvinova, Maria / Byrne, Thomas / Zardini, Agnese / Poletti, Piero / Merler, Stefano / Mutebi, John-Paul / Townsend, John / Ajelli, Marco

Elsevier B.V. Acta Tropica. 20232023 Apr. 01, Feb. 01, v. 240 p.106833-

2023

Abstract	Mosquito-borne diseases are a major global public health concern and mosquito surveillance systems are essential for the implementation of effective mosquito control strategies. The objective of our study is to determine the spatiotemporal distribution of vector mosquito species in Maricopa County, AZ from 2011 to 2021, and to identify the hotspot areas for West Nile virus (WNV) and St. Louis Encephalitis virus (SLEV) transmission in 2021. The Maricopa County Mosquito Control surveillance system utilizes BG-Sentinel and EVS-CDC traps throughout the entire urban and suburban areas of the county. We estimated specific mosquito species relative abundance per unit area using the Kernel density estimator in ArcGIS 10.2. We calculated the distance between all traps in the surveillance system and created a 4 km buffer radius around each trap to calculate the extent to which each trap deviated from the mean number of Culex quinquefasciatus and Culex tarsalis collected in 2021. Our results show that vector mosquito species are widely distributed and abundant in the urban areas of Maricopa County. A total of 691,170Cx. quinquefasciatus, 542,733 Cx. tarsalis, and 292,305 Aedes aegypti were collected from 2011 to 2022. The relative abundance of Ae. aegypti was highly seasonal peaking in the third and fourth quarters of the year. Culex quinquefasciatus, on the other hand, was abundant throughout the year with several regions consistently yielding high numbers of mosquitoes. Culex tarsalis was abundant but it only reached high numbers in well-defined areas near irrigated landscapes. We also detected high levels of heterogeneity in the risk of WNV and SLEV transmission to humans disregarding traps geographical proximity. The well-defined species-specific spatiotemporal and geographical patterns found in this study can be used to inform vector control operations.
Keywords	Aedes aegypti ; Culex quinquefasciatus ; Culex tarsalis ; Saint Louis encephalitis virus ; West Nile virus ; arboviruses ; irrigation ; monitoring ; mosquito control ; public health ; risk ; species abundance ; vector control ; Arizona ; Arbovirus
Language	English
Dates of publication	2023-0201
Publishing place	Elsevier B.V.
Document type	Article ; Online
ZDB-ID	210415-5
ISSN	1873-6254 ; 0001-706X
ISSN (online)	1873-6254
ISSN	0001-706X
DOI	10.1016/j.actatropica.2023.106833
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Article ; Online: Priority age targets for COVID-19 vaccination in Ethiopia under limited vaccine supply

Margherita Galli / Agnese Zardini / Worku Nigussa Gamshie / Stefano Santini / Ademe Tsegaye / Filippo Trentini / Valentina Marziano / Giorgio Guzzetta / Mattia Manica / Valeria d’Andrea / Giovanni Putoto / Fabio Manenti / Marco Ajelli / Piero Poletti / Stefano Merler

Scientific Reports, Vol 13, Iss 1, Pp 1-

2023 Volume 12

Abstract: Abstract The worldwide inequitable access to vaccination claims for a re-assessment of policies that could minimize the COVID-19 burden in low-income countries. Nine months after the launch of the national vaccination program in March 2021, only 3.4% of ... ...

Abstract	Abstract The worldwide inequitable access to vaccination claims for a re-assessment of policies that could minimize the COVID-19 burden in low-income countries. Nine months after the launch of the national vaccination program in March 2021, only 3.4% of the Ethiopian population received two doses of COVID-19 vaccine. We used a SARS-CoV-2 transmission model to estimate the level of immunity accrued before the launch of vaccination in the Southwest Shewa Zone (SWSZ) and to evaluate the impact of alternative age priority vaccination targets in a context of limited vaccine supply. The model was informed with available epidemiological evidence and detailed contact data collected across different geographical settings (urban, rural, or remote). We found that, during the first year of the pandemic, the mean proportion of critical cases occurred in SWSZ attributable to infectors under 30 years of age would range between 24.9 and 48.0%, depending on the geographical setting. During the Delta wave, the contribution of this age group in causing critical cases was estimated to increase on average to 66.7–70.6%. Our findings suggest that, when considering the vaccine product available at the time (ChAdOx1 nCoV-19; 65% efficacy against infection after 2 doses), prioritizing the elderly for vaccination remained the best strategy to minimize the disease burden caused by Delta, irrespectively of the number of available doses. Vaccination of all individuals aged ≥ 50 years would have averted 40 (95%PI: 18–60), 90 (95%PI: 61–111), and 62 (95%PI: 21–108) critical cases per 100,000 residents in urban, rural, and remote areas, respectively. Vaccination of all individuals aged ≥ 30 years would have averted an average of 86–152 critical cases per 100,000 individuals, depending on the setting considered. Despite infections among children and young adults likely caused 70% of critical cases during the Delta wave in SWSZ, most vulnerable ages should remain a key priority target for vaccination against COVID-19.
Keywords	Medicine ; R ; Science ; Q
Subject code	360
Language	English
Publishing date	2023-04-01T00:00:00Z
Publisher	Nature Portfolio
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Estimating SARS-CoV-2 transmission in educational settings: A retrospective cohort study.

Manica, Mattia / Poletti, Piero / Deandrea, Silvia / Mosconi, Giansanto / Ancarani, Cinzia / Lodola, Silvia / Guzzetta, Giorgio / d'Andrea, Valeria / Marziano, Valentina / Zardini, Agnese / Trentini, Filippo / Odone, Anna / Tirani, Marcello / Ajelli, Marco / Merler, Stefano

Influenza and other respiratory viruses

2022 Volume 17, Issue 1, Page(s) e13049

Abstract: Background: School closures and distance learning have been extensively adopted to counter the COVID-19 pandemic. However, the contribution of school transmission to the spread of SARS-CoV-2 remains poorly quantified.: Methods: We analyzed ... ...

Abstract	Background: School closures and distance learning have been extensively adopted to counter the COVID-19 pandemic. However, the contribution of school transmission to the spread of SARS-CoV-2 remains poorly quantified. Methods: We analyzed transmission patterns associated with 976 SARS-CoV-2 exposure events, involving 460 positive individuals, as identified in early 2021 through routine surveillance and an extensive screening conducted on students, school personnel, and their household members in a small Italian municipality. In addition to population screenings and contact-tracing operations, reactive closures of class and schools were implemented. Results: From the analysis of 152 clear infection episodes and 584 exposure events identified by epidemiological investigations, we estimated that approximately 50%, 21%, and 29% of SARS-CoV-2 transmission was associated with household, school, and community contacts, respectively. We found substantial transmission heterogeneities, with 20% positive individuals causing 75% to 80% of ascertained infection episodes. A higher proportion of infected individuals causing onward transmission was found among students (46.2% vs. 25%, on average), who also caused a markedly higher number of secondary cases (mean: 1.03 vs. 0.35). By reconstructing likely transmission chains from the entire set of exposures identified during contact-tracing operations, we found that clusters originated from students or school personnel were associated with a larger average cluster size (3.32 vs. 1.15) and a larger average number of generations in the transmission chain (1.56 vs. 1.17). Conclusions: Uncontrolled SARS-CoV-2 transmission at school could disrupt the regular conduct of teaching activities, likely seeding the transmission into other settings, and increasing the burden on contact-tracing operations.
MeSH term(s)	Humans ; SARS-CoV-2 ; COVID-19/epidemiology ; Pandemics/prevention & control ; Retrospective Studies ; Contact Tracing ; Schools
Language	English
Publishing date	2022-09-20
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2274538-5
ISSN	1750-2659 ; 1750-2640
ISSN (online)	1750-2659
ISSN	1750-2640
DOI	10.1111/irv.13049
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Article ; Online: Estimating the potential risk of transmission of arboviruses in the Americas and Europe: a modelling study.

Zardini, Agnese / Menegale, Francesco / Gobbi, Andrea / Manica, Mattia / Guzzetta, Giorgio / d'Andrea, Valeria / Marziano, Valentina / Trentini, Filippo / Montarsi, Fabrizio / Caputo, Beniamino / Solimini, Angelo / Marques-Toledo, Cecilia / Wilke, André B B / Rosà, Roberto / Marini, Giovanni / Arnoldi, Daniele / Pastore Y Piontti, Ana / Pugliese, Andrea / Capelli, Gioia /

Della Torre, Alessandra / Teixeira, Mauro M / Beier, John C / Rizzoli, Annapaola / Vespignani, Alessandro / Ajelli, Marco / Merler, Stefano / Poletti, Piero

The Lancet. Planetary health

2024 Volume 8, Issue 1, Page(s) e30–e40

Abstract: Background: Estimates of the spatiotemporal distribution of different mosquito vector species and the associated risk of transmission of arboviruses are key to design adequate policies for preventing local outbreaks and reducing the number of human ... ...

Abstract	Background: Estimates of the spatiotemporal distribution of different mosquito vector species and the associated risk of transmission of arboviruses are key to design adequate policies for preventing local outbreaks and reducing the number of human infections in endemic areas. In this study, we quantified the abundance of Aedes albopictus and Aedes aegypti and the local transmission potential for three arboviral infections at an unprecedented spatiotemporal resolution in areas where no entomological surveillance is available. Methods: We developed a computational model to quantify the daily abundance of Aedes mosquitoes, leveraging temperature and precipitation records. The model was calibrated on mosquito surveillance data collected in 115 locations in Europe and the Americas between 2007 and 2018. Model estimates were used to quantify the reproduction number of dengue virus, Zika virus, and chikungunya in Europe and the Americas, at a high spatial resolution. Findings: In areas colonised by both Aedes species, A aegypti was estimated to be the main vector for the transmission of dengue virus, Zika virus, and chikungunya, being associated with a higher estimate of R Interpretation: Our results provide a comprehensive overview of the transmission potential of arboviral diseases in Europe and the Americas, highlighting areas where surveillance and mosquito control capacities should be prioritised. Funding: EU and Ministero dell'Università e della Ricerca, Italy (Piano Nazionale di Ripresa e Resilienza Extended Partnership initiative on Emerging Infectious Diseases); EU (Horizon 2020); Ministero dell'Università e della Ricerca, Italy (Progetti di ricerca di Rilevante Interesse Nazionale programme); Brazilian National Council of Science, Technology and Innovation; Ministry of Health, Brazil; and Foundation of Research for Minas Gerais, Brazil.
MeSH term(s)	Humans ; Animals ; Arboviruses ; Chikungunya Fever/epidemiology ; Europe/epidemiology ; Aedes ; Zika Virus ; Zika Virus Infection/epidemiology
Language	English
Publishing date	2024-01-10
Publishing country	Netherlands
Document type	Review ; Journal Article ; Research Support, Non-U.S. Gov't
ISSN	2542-5196
ISSN (online)	2542-5196
DOI	10.1016/S2542-5196(23)00252-8
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Article ; Online: SARS-CoV-2 transmission patterns in educational settings during the Alpha wave in Reggio-Emilia, Italy.

Epidemics

2023 Volume 44, Page(s) 100712

Abstract: Different monitoring and control policies have been implemented in schools to minimize the spread of SARS-CoV-2. Transmission in schools has been hard to quantify due to the large proportion of asymptomatic carriers in young individuals. We applied a ... ...

Abstract	Different monitoring and control policies have been implemented in schools to minimize the spread of SARS-CoV-2. Transmission in schools has been hard to quantify due to the large proportion of asymptomatic carriers in young individuals. We applied a Bayesian approach to reconstruct the transmission chains between 284 SARS-CoV-2 infections ascertained during 87 school outbreak investigations conducted between March and April 2021 in Italy. Under the policy of reactive quarantines, we found that 42.5% (95%CrI: 29.5-54.3%) of infections among school attendees were caused by school contacts. The mean number of secondary cases infected at school by a positive individual during in-person education was estimated to be 0.33 (95%CrI: 0.23-0.43), with marked heterogeneity across individuals. Specifically, we estimated that only 26.0% (95%CrI: 17.6-34.1%) of students and school personnel who tested positive during in-person education caused at least one secondary infection at school. Positive individuals who attended school for at least 6 days before being isolated or quarantined infected on average 0.49 (95%CrI: 0.14-0.83) secondary cases. Our findings provide quantitative insights on the contribution of school transmission to the spread of SARS-CoV-2 in young individuals. Identifying positive cases within 5 days after exposure to their infector could reduce onward transmission at school by at least 30%.
MeSH term(s)	Humans ; SARS-CoV-2 ; COVID-19/epidemiology ; Bayes Theorem ; Schools ; Italy/epidemiology
Language	English
Publishing date	2023-08-03
Publishing country	Netherlands
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2467993-8
ISSN	1878-0067 ; 1755-4365
ISSN (online)	1878-0067
ISSN	1755-4365
DOI	10.1016/j.epidem.2023.100712
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Article ; Online: Estimating SARS-CoV-2 infections and associated changes in COVID-19 severity and fatality.

Marziano, Valentina / Guzzetta, Giorgio / Menegale, Francesco / Sacco, Chiara / Petrone, Daniele / Mateo Urdiales, Alberto / Del Manso, Martina / Bella, Antonino / Fabiani, Massimo / Vescio, Maria Fenicia / Riccardo, Flavia / Poletti, Piero / Manica, Mattia / Zardini, Agnese / d'Andrea, Valeria / Trentini, Filippo / Stefanelli, Paola / Rezza, Giovanni / Palamara, Anna Teresa /

Brusaferro, Silvio / Ajelli, Marco / Pezzotti, Patrizio / Merler, Stefano

Influenza and other respiratory viruses

2023 Volume 17, Issue 8, Page(s) e13181

Abstract: Background: The difficulty in identifying SARS-CoV-2 infections has not only been the major obstacle to control the COVID-19 pandemic but also to quantify changes in the proportion of infections resulting in hospitalization, intensive care unit (ICU) ... ...

Abstract	Background: The difficulty in identifying SARS-CoV-2 infections has not only been the major obstacle to control the COVID-19 pandemic but also to quantify changes in the proportion of infections resulting in hospitalization, intensive care unit (ICU) admission, or death. Methods: We developed a model of SARS-CoV-2 transmission and vaccination informed by official estimates of the time-varying reproduction number to estimate infections that occurred in Italy between February 2020 and 2022. Model outcomes were compared with the Italian National surveillance data to estimate changes in the SARS-CoV-2 infection ascertainment ratio (IAR), infection hospitalization ratio (IHR), infection ICU ratio (IIR), and infection fatality ratio (IFR) in five different sub-periods associated with the dominance of the ancestral lineages and Alpha, Delta, and Omicron BA.1 variants. Results: We estimate that, over the first 2 years of pandemic, the IAR ranged between 15% and 40% (range of 95%CI: 11%-61%), with a peak value in the second half of 2020. The IHR, IIR, and IFR consistently decreased throughout the pandemic with 22-44-fold reductions between the initial phase and the Omicron period. At the end of the study period, we estimate an IHR of 0.24% (95%CI: 0.17-0.36), IIR of 0.015% (95%CI: 0.011-0.023), and IFR of 0.05% (95%CI: 0.04-0.08). Conclusions: Since 2021, changes in the dominant SARS-CoV-2 variant, vaccination rollout, and the shift of infection to younger ages have reduced SARS-CoV-2 infection ascertainment. The same factors, combined with the improvement of patient management and care, contributed to a massive reduction in the severity and fatality of COVID-19.
MeSH term(s)	Humans ; COVID-19/epidemiology ; SARS-CoV-2 ; Pandemics ; Hospitalization
Language	English
Publishing date	2023-08-16
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2274538-5
ISSN	1750-2659 ; 1750-2640
ISSN (online)	1750-2659
ISSN	1750-2640
DOI	10.1111/irv.13181
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