Who infected the reported cases? Evidence from 678,482 COVID-19 cases with identified infector collected in routine surveillance in the Netherlands, 2020-2022.
- 1National Institute for Public Health and the Environment (RIVM)
Abstract
Background During infectious disease outbreaks, characteristics of reported cases are routinely collected. These give information on becoming infected but not on infecting others. We assess whether linking infectees to infectors, together with their characteristics, can help understand transmission. Methods From the start of the COVID-19 pandemic in the Netherlands, reported cases were asked to identify their most probable infector in routine surveillance, enabling the linking of cases. We assess for the period 27 February 2020 - 11 April 2022 whether the infectees of these transmission pairs are representative of all reported cases, whether the transmission pairs yield verifiable estimates of epidemiological characteristics (here the serial interval), and whether they provide information on transmission that cannot be obtained otherwise. Results Of 8,003,008 reported cases, 678,482 (8.5%) could be linked to their most probable infector. These infectees were largely representative of the reported cases regarding age group, sex, and geographical location. The mean serial interval of 3.6 days (sd 3.4 days) from transmission pairs aligns with literature. Transmissions between age groups largely follow known contact patterns. Most transmissions in September 2021 occurred between persons who were not (fully) vaccinated, indicating the effectiveness of the vaccine, and relatively few between persons with different vaccination status, indicating assortative mixing in vaccination status. Conclusion Transmission pairs can be efficiently collected in routine surveillance, providing insight into disease transmission. The current post-pandemic period provides an excellent opportunity to adjust reporting systems for linking infectees to their most probable infector as preparation for future outbreaks.
Related
- Higher general practice-reported health condition rates among adolescent and young adult (18−39 years) cancer survivors up to 22 years after diagnosis in the Netherlands: a retrospective cohort study
- County-level associations between passively collected walking and bicycling and self-reported nonoccupational physical activity data
- Detection of Plasmodium vivax and Plasmodium falciparum using colorimetric loop-mediated isothermal amplification from dried blood spots collected in active and passive malaria surveillance in the Peruvian Amazon
- Detection of Plasmodium falciparum-infected Anopheles sergentii with reduced insecticide net susceptibility in a dryland ecosystem of the Kenyan Rift Valley: implications for malaria surveillance and vector control
- Artificial intelligence–enabled nursing surveillance for pediatric cancer immunotherapy: integrating biomarkers, patient-reported outcomes, and long-term toxicity management
BibTeX
@misc{backer2026infected,
title = {{Who infected the reported cases? Evidence from 678,482 COVID-19 cases with identified infector collected in routine surveillance in the Netherlands, 2020-2022.}},
author = {J. A. Backer and K. Y. Leung and S. P. Andeweg and J. Van de Kassteele and I. Veldhuijzen and S. Hahne and J. Wallinga},
howpublished = {medRxiv},
year = {2026},
month = may,
doi = {10.64898/2026.05.15.26347859},
url = {https://www.medrxiv.org/content/10.64898/2026.05.15.26347859v2},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Who infected the reported cases? Evidence from 678,482 COVID-19 cases with identified infector collected in routine surveillance in the Netherlands, 2020-2022.
AU - J. A. Backer
AU - K. Y. Leung
AU - S. P. Andeweg
AU - J. Van de Kassteele
AU - I. Veldhuijzen
AU - S. Hahne
AU - J. Wallinga
PY - 2026
DA - 2026/05/15
PB - medRxiv
DO - 10.64898/2026.05.15.26347859
UR - https://www.medrxiv.org/content/10.64898/2026.05.15.26347859v2
AB - Background During infectious disease outbreaks, characteristics of reported cases are routinely collected. These give information on becoming infected but not on infecting others. We assess whether linking infectees to infectors, together with their characteristics, can help understand transmission. Methods From the start of the COVID-19 pandemic in the Netherlands, reported cases were asked to identify their most probable infector in routine surveillance, enabling the linking of cases. We assess for the period 27 February 2020 - 11 April 2022 whether the infectees of these transmission pairs are representative of all reported cases, whether the transmission pairs yield verifiable estimates of epidemiological characteristics (here the serial interval), and whether they provide information on transmission that cannot be obtained otherwise. Results Of 8,003,008 reported cases, 678,482 (8.5%) could be linked to their most probable infector. These infectees were largely representative of the reported cases regarding age group, sex, and geographical location. The mean serial interval of 3.6 days (sd 3.4 days) from transmission pairs aligns with literature. Transmissions between age groups largely follow known contact patterns. Most transmissions in September 2021 occurred between persons who were not (fully) vaccinated, indicating the effectiveness of the vaccine, and relatively few between persons with different vaccination status, indicating assortative mixing in vaccination status. Conclusion Transmission pairs can be efficiently collected in routine surveillance, providing insight into disease transmission. The current post-pandemic period provides an excellent opportunity to adjust reporting systems for linking infectees to their most probable infector as preparation for future outbreaks.
ER -