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Article ; Online: Estimation of the infection attack rate of mumps in an outbreak among college students using paired serology.

van Boven, Michiel / Backer, Jantien A / Veldhuijzen, Irene / Gomme, Justin / van Binnendijk, Rob / Kaaijk, Patricia

2024 Volume 46, Page(s) 100751

Abstract: Mumps virus is a highly transmissible pathogen that is effectively controlled in countries with high vaccination coverage. Nevertheless, outbreaks have occurred worldwide over the past decades in vaccinated populations. Here we analyse an outbreak of ... ...

Abstract	Mumps virus is a highly transmissible pathogen that is effectively controlled in countries with high vaccination coverage. Nevertheless, outbreaks have occurred worldwide over the past decades in vaccinated populations. Here we analyse an outbreak of mumps virus genotype G among college students in the Netherlands over the period 2009-2012 using paired serological data. To identify infections in the presence of preexisting antibodies we compared mumps specific serum IgG concentrations in two consecutive samples (n=746), whereby the first sample was taken when students started their study prior to the outbreaks, and the second sample was taken 2-5 years later. We fit a binary mixture model to the data. The two mixing distributions represent uninfected and infected classes. Throughout we assume that the infection probability increases with the ratio of antibody concentrations of the second to first sample. The estimated infection attack rate in this study is higher than reported earlier (0.095 versus 0.042). The analyses yield probabilistic classifications of participants, which are mostly quite precise owing to the high intraclass correlation of samples in uninfected participants (0.85, 95%CrI: 0.82-0.87). The estimated probability of infection increases with decreasing antibody concentration in the pre-outbreak sample, such that the probability of infection is 0.12 (95%CrI: 0.10-0.13) for the lowest quartile of the pre-outbreak samples and 0.056 (95%CrI: 0.044-0.068) for the highest quartile. We discuss the implications of these insights for the design of booster vaccination strategies.
MeSH term(s)	Humans ; Mumps/epidemiology ; Mumps/prevention & control ; Incidence ; Mumps virus/genetics ; Disease Outbreaks/prevention & control ; Students
Language	English
Publishing date	2024-03-01
Publishing country	Netherlands
Document type	Journal Article
ZDB-ID	2467993-8
ISSN	1878-0067 ; 1755-4365
ISSN (online)	1878-0067
ISSN	1755-4365
DOI	10.1016/j.epidem.2024.100751
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Article ; Online: Contact patterns of older adults with and without frailty in the Netherlands during the COVID-19 pandemic.

Backer, Jantien A / van de Kassteele, Jan / El Fakiri, Fatima / Hens, Niel / Wallinga, Jacco

BMC public health

2023 Volume 23, Issue 1, Page(s) 1829

Abstract: Background: During the COVID-19 pandemic, social distancing measures were imposed to protect the population from exposure, especially older adults and people with frailty, who have the highest risk for severe outcomes. These restrictions greatly reduced ...

Abstract	Background: During the COVID-19 pandemic, social distancing measures were imposed to protect the population from exposure, especially older adults and people with frailty, who have the highest risk for severe outcomes. These restrictions greatly reduced contacts in the general population, but little was known about behaviour changes among older adults and people with frailty themselves. Our aim was to quantify how COVID-19 measures affected the contact behaviour of older adults and how this differed between older adults with and without frailty. Methods: In 2021, a contact survey was carried out among people aged 70 years and older in the Netherlands. A random sample of persons per age group (70-74, 75-79, 80-84, 85-89, and 90 +) and gender was invited to participate, either during a period with stringent (April 2021) or moderate (October 2021) measures. Participants provided general information on themselves, including their frailty, and they reported characteristics of all persons with whom they had face-to-face contact on a given day over the course of a full week. Results: In total, 720 community-dwelling older adults were included (overall response rate of 15%), who reported 16,505 contacts. During the survey period with moderate measures, participants without frailty had significantly more contacts outside their household than participants with frailty. Especially for females, frailty was a more informative predictor of the number of contacts than age. During the survey period with stringent measures, participants with and without frailty had significantly lower numbers of contacts compared to the survey period with moderate measures. The reduction of the number of contacts was largest for the eldest participants without frailty. As they interact mostly with adults of a similar high age who are likely frail, this reduction of the number of contacts indirectly protects older adults with frailty from SARS-CoV-2 exposure. Conclusions: The results of this study reveal that social distancing measures during the COVID-19 pandemic differentially affected the contact patterns of older adults with and without frailty. The reduction of contacts may have led to the direct protection of older adults in general but also to the indirect protection of older adults with frailty.
MeSH term(s)	Female ; Humans ; Aged ; Aged, 80 and over ; COVID-19/epidemiology ; SARS-CoV-2 ; Frailty/epidemiology ; Netherlands/epidemiology ; Pandemics
Language	English
Publishing date	2023-09-20
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ZDB-ID	2041338-5
ISSN	1471-2458 ; 1471-2458
ISSN (online)	1471-2458
ISSN	1471-2458
DOI	10.1186/s12889-023-16725-1
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Article ; Online: Contact patterns of older adults with and without frailty in the Netherlands during the COVID-19 pandemic

Jantien A. Backer / Jan van de Kassteele / Fatima El Fakiri / Niel Hens / Jacco Wallinga

BMC Public Health, Vol 23, Iss 1, Pp 1-

2023 Volume 12

Abstract: Abstract Background During the COVID-19 pandemic, social distancing measures were imposed to protect the population from exposure, especially older adults and people with frailty, who have the highest risk for severe outcomes. These restrictions greatly ... ...

Abstract	Abstract Background During the COVID-19 pandemic, social distancing measures were imposed to protect the population from exposure, especially older adults and people with frailty, who have the highest risk for severe outcomes. These restrictions greatly reduced contacts in the general population, but little was known about behaviour changes among older adults and people with frailty themselves. Our aim was to quantify how COVID-19 measures affected the contact behaviour of older adults and how this differed between older adults with and without frailty. Methods In 2021, a contact survey was carried out among people aged 70 years and older in the Netherlands. A random sample of persons per age group (70–74, 75–79, 80–84, 85–89, and 90 +) and gender was invited to participate, either during a period with stringent (April 2021) or moderate (October 2021) measures. Participants provided general information on themselves, including their frailty, and they reported characteristics of all persons with whom they had face-to-face contact on a given day over the course of a full week. Results In total, 720 community-dwelling older adults were included (overall response rate of 15%), who reported 16,505 contacts. During the survey period with moderate measures, participants without frailty had significantly more contacts outside their household than participants with frailty. Especially for females, frailty was a more informative predictor of the number of contacts than age. During the survey period with stringent measures, participants with and without frailty had significantly lower numbers of contacts compared to the survey period with moderate measures. The reduction of the number of contacts was largest for the eldest participants without frailty. As they interact mostly with adults of a similar high age who are likely frail, this reduction of the number of contacts indirectly protects older adults with frailty from SARS-CoV-2 exposure. Conclusions The results of this study reveal that social distancing measures ...
Keywords	Contact survey ; Older adults ; Frailty ; Behaviour change ; COVID-19 pandemic ; Control measures ; Public aspects of medicine ; RA1-1270
Subject code	150
Language	English
Publishing date	2023-09-01T00:00:00Z
Publisher	BMC
Document type	Article ; Online
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Article ; Online: Time Scales of Human Mpox Transmission in The Netherlands.

Miura, Fuminari / Backer, Jantien A / van Rijckevorsel, Gini / Bavalia, Roisin / Raven, Stijn / Petrignani, Mariska / Ainslie, Kylie E C / Wallinga, Jacco

The Journal of infectious diseases

2023 Volume 229, Issue 3, Page(s) 800–804

Abstract: Mpox has spread rapidly to many countries in nonendemic regions. After reviewing detailed exposure histories of 109 pairs of mpox cases in the Netherlands, we identified 34 pairs where transmission was likely and the infectee reported a single potential ... ...

Abstract	Mpox has spread rapidly to many countries in nonendemic regions. After reviewing detailed exposure histories of 109 pairs of mpox cases in the Netherlands, we identified 34 pairs where transmission was likely and the infectee reported a single potential infector with a mean serial interval of 10.1 days (95% credible interval, 6.6-14.7 days). Further investigation into pairs from 1 regional public health service revealed that presymptomatic transmission may have occurred in 5 of 18 pairs. These findings emphasize that precaution remains key, regardless of the presence of recognizable symptoms of mpox.
MeSH term(s)	Humans ; Netherlands ; Mpox (monkeypox)
Language	English
Publishing date	2023-04-01
Publishing country	United States
Document type	Journal Article
ZDB-ID	3019-3
ISSN	1537-6613 ; 0022-1899
ISSN (online)	1537-6613
ISSN	0022-1899
DOI	10.1093/infdis/jiad091
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Article ; Online: Projecting COVID-19 intensive care admissions in the Netherlands for policy advice: February 2020 to January 2021

Klinkenberg, Don / Backer, Jantien A. / de Keizer, Nicolette F. / Wallinga, Jacco

medRxiv

Abstract: Introduction: Model projections of COVID-19 incidence into the future help policy makers about decisions to implement or lift control measures. During 2020, policy makers in the Netherlands were informed on a weekly basis with short-term projections of ... ...

Abstract	Introduction: Model projections of COVID-19 incidence into the future help policy makers about decisions to implement or lift control measures. During 2020, policy makers in the Netherlands were informed on a weekly basis with short-term projections of COVID-19 intensive care unit (ICU) admissions. Here we present the model and the procedure by which it was updated. Methods: the projections were produced using an age-structured transmission model. A consistent, incremental update procedure that integrated all new surveillance and hospital data was conducted weekly. First, up-to-date estimates for most parameter values were obtained through re-analysis of all data sources. Then, estimates were made for changes in the age-specific contact rates in response to policy changes. Finally, a piecewise constant transmission rate was estimated by fitting the model to reported daily ICU admissions, with a change point analysis guided by Akaike9s Information Criterion. Results: The model and update procedure allowed us to make mostly accurate weekly projections, accounting for recent and future policy changes, and to adapt the estimated effectiveness of the policy changes based only on the natural accumulation of incoming data. Discussion: The model incorporates basic epidemiological principles and most model parameters were estimated per data source. Therefore, it had potential to be adapted to a more complex epidemiological situation, as it would develop after 2020.
Keywords	covid19
Language	English
Publishing date	2023-07-03
Publisher	Cold Spring Harbor Laboratory Press
Document type	Article ; Online
DOI	10.1101/2023.06.30.23291989
Database	COVID19

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Article ; Online: Incubation period of 2019 novel coronavirus (2019-nCoV) infections among travellers from Wuhan, China, 20-28 January 2020.

Backer, Jantien A / Klinkenberg, Don / Wallinga, Jacco

Euro surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin

2020 Volume 25, Issue 5

Abstract: A novel coronavirus (2019-nCoV) is causing an outbreak of viral pneumonia that started in Wuhan, China. Using the travel history and symptom onset of 88 confirmed cases that were detected outside Wuhan in the early outbreak phase, we estimate the mean ... ...

Abstract	A novel coronavirus (2019-nCoV) is causing an outbreak of viral pneumonia that started in Wuhan, China. Using the travel history and symptom onset of 88 confirmed cases that were detected outside Wuhan in the early outbreak phase, we estimate the mean incubation period to be 6.4 days (95% credible interval: 5.6-7.7), ranging from 2.1 to 11.1 days (2.5th to 97.5th percentile). These values should help inform 2019-nCoV case definitions and appropriate quarantine durations.
MeSH term(s)	Betacoronavirus/pathogenicity ; COVID-19 ; China/epidemiology ; Coronavirus Infections/diagnosis ; Coronavirus Infections/epidemiology ; Coronavirus Infections/transmission ; Humans ; Infectious Disease Incubation Period ; Pneumonia, Viral/diagnosis ; Pneumonia, Viral/epidemiology ; Pneumonia, Viral/transmission ; SARS-CoV-2 ; Severe Acute Respiratory Syndrome/diagnosis ; Severe Acute Respiratory Syndrome/transmission ; Travel ; Virus Latency
Keywords	covid19
Language	English
Publishing date	2020-01-31
Publishing country	Sweden
Document type	Journal Article
ZDB-ID	1338803-4
ISSN	1560-7917 ; 1025-496X
ISSN (online)	1560-7917
ISSN	1025-496X
DOI	10.2807/1560-7917.ES.2020.25.5.2000062
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Article ; Online: Contact patterns of frail and non-frail elderly persons in the Netherlands during the COVID-19 pandemic

Backer, Jantien A / van de Kassteele, Jan / Fakiri, Fatima El / Hens, Niel / Wallinga, Jacco

medRxiv

Abstract: Background During the COVID-19 pandemic social distancing measures were imposed to protect the population from exposure, especially elderly and frail persons who have the highest risk for severe outcomes. These restrictions greatly reduced contacts in ... ...

Abstract	Background During the COVID-19 pandemic social distancing measures were imposed to protect the population from exposure, especially elderly and frail persons who have the highest risk for severe outcomes. These restrictions greatly reduced contacts in the general population, but little is known about behaviour changes among elderly and frail persons themselves. Our aim was to quantify how COVID-19 measures affected contact behaviour of elderly and how this differed between frail and non-frail elderly. Methods In 2021 a contact survey was carried out among persons aged 70 years and older in the Netherlands. A random sample of persons per age group (70-74, 75-79, 80-84, 85-89, 90+) and gender was invited to participate, either during a period with stringent (April 2021) or moderate (October 2021) measures. Participants provided general information on themselves including their frailty, and reported characteristics of all persons with whom they had face-to-face contact on a given day, over the course of a full week. Results In total 720 community-dwelling elderly persons were included (overall response rate of 15%), who reported 16,505 contacts. During the survey period with moderate measures, non-frail participants had significantly more contacts outside their household than frail participants. Especially for women, frailty was a more informative predictor for number of contacts than age. During the survey period with stringent measures, frail and non-frail participants had significantly lower numbers of contacts compared to the survey period with moderate measures. The reduction of number of contacts was largest for the eldest non-frail participants. As they likely interact closely with highly aged and highly frail persons, this reduction of number of contacts indirectly protects frail elderly from SARS-CoV-2 exposure. Conclusions The results of this study reveal that social distancing measures during the COVID-19 pandemic differentially affected the contact patterns of frail and non-frail elderly. The reduction of contacts may have led to direct protection of elderly persons in general but also to indirect protection of frail elderly.
Keywords	covid19
Language	English
Publishing date	2023-05-11
Publisher	Cold Spring Harbor Laboratory Press
Document type	Article ; Online
DOI	10.1101/2023.05.09.23289550
Database	COVID19

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Article ; Online: Estimating social contact rates for the COVID-19 pandemic using Google mobility and pre-pandemic contact surveys

Prestige, Em / Coletti, Pietro / Backer, Jantien A. / Davies, Nicholas J. / Edmunds, W. John / Jarvis, Christopher I.

medRxiv

Abstract: During the COVID-19 pandemic, aggregated mobility data was frequently used to estimate changing social contact rates. By taking contact matrices estimated pre-pandemic, and transforming these using pandemic–era mobility data, epidemiologists attempted to ...

Abstract	During the COVID-19 pandemic, aggregated mobility data was frequently used to estimate changing social contact rates. By taking contact matrices estimated pre-pandemic, and transforming these using pandemic–era mobility data, epidemiologists attempted to predict the number of contacts individuals were expected to have during large-scale restrictions. This study explores the most effective method for this transformation, comparing it to the accuracy of pandemic–era contact surveys. We compared four methods for scaling synthetic contact matrices: two using fitted regression models and two using ″na&iumlve″ mobility or mobility squared models. The regression models were fitted using CoMix contact survey and Google mobility data from the UK over March 2020 – March 2021. The four models were then used to scale synthetic contact matrices—a representation of pre–pandemic behaviour—using mobility data from the UK, Belgium and the Netherlands to predict the number of contacts expected in ″work″ and ″other″ settings for a given mobility level. We then compared partial reproduction numbers estimated from the four models with those calculated directly from CoMix contact matrices across the three countries. The accuracy of each model was assessed using root mean squared error. The fitted regression models had substantially more accurate predictions than the na&iumlve models, even when the regression models were applied to Belgium and the Netherlands. Across all countries investigated, the na&iumlve model using mobility alone was the least accurate, followed by the na&iumlve model using mobility squared. When attempting to estimate social contact rates during a pandemic without the resources available to conduct contact surveys, using a model fitted to data from another pandemic context is likely to be an improvement over using a ″na&iumlve″ model based on raw mobility data. If a na&iumlve model is to be used, mobility squared may be a better predictor of contact rates than mobility per se.
Keywords	covid19
Language	English
Publishing date	2023-12-19
Publisher	Cold Spring Harbor Laboratory Press
Document type	Article ; Online
DOI	10.1101/2023.12.19.23300209
Database	COVID19

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Article ; Online: Transmissibility of SARS-CoV-2 among fully vaccinated individuals.

Knol, Mirjam J / Backer, Jantien A / de Melker, Hester E / van den Hof, Susan / Gier, Brechje de

The Lancet. Infectious diseases

2021 Volume 22, Issue 1, Page(s) 16–17

MeSH term(s)	COVID-19 ; Diagnostic Tests, Routine ; Humans ; SARS-CoV-2
Language	English
Publishing date	2021-12-22
Publishing country	United States
Document type	Letter ; Comment
ZDB-ID	2061641-7
ISSN	1474-4457 ; 1473-3099
ISSN (online)	1474-4457
ISSN	1473-3099
DOI	10.1016/S1473-3099(21)00763-5
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Zs.A 5743: Show issues

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Article ; Online: Spatiotemporal Analysis of the 2014 Ebola Epidemic in West Africa.

Jantien A Backer / Jacco Wallinga

PLoS Computational Biology, Vol 12, Iss 12, p e

2016 Volume 1005210

Abstract: In 2014-2016, Guinea, Sierra Leone and Liberia in West Africa experienced the largest and longest Ebola epidemic since the discovery of the virus in 1976. During the epidemic, incidence data were collected and published at increasing resolution. To ... ...

Abstract	In 2014-2016, Guinea, Sierra Leone and Liberia in West Africa experienced the largest and longest Ebola epidemic since the discovery of the virus in 1976. During the epidemic, incidence data were collected and published at increasing resolution. To monitor the epidemic as it spread within and between districts, we develop an analysis method that exploits the full spatiotemporal resolution of the data by combining a local model for time-varying effective reproduction numbers with a gravity-type model for spatial dispersion of the infection. We test this method in simulations and apply it to the weekly incidences of confirmed and probable cases per district up to June 2015, as reported by the World Health Organization. Our results indicate that, of the newly infected cases, only a small percentage, between 4% and 10%, migrates to another district, and a minority of these migrants, between 0% and 23%, leave their country. The epidemics in the three countries are found to be similar in estimated effective reproduction numbers, and in the probability of importing infection into a district. The countries might have played different roles in cross-border transmissions, although a sensitivity analysis suggests that this could also be related to underreporting. The spatiotemporal analysis method can exploit available longitudinal incidence data at different geographical locations to monitor local epidemics, determine the extent of spatial spread, reveal the contribution of local and imported cases, and identify sources of introductions in uninfected areas. With good quality data on incidence, this data-driven method can help to effectively control emerging infections.
Keywords	Biology (General) ; QH301-705.5
Language	English
Publishing date	2016-12-01T00:00:00Z
Publisher	Public Library of Science (PLoS)
Document type	Article ; Online
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