Elimination of covid-19: beware of surveillance bias

Tancredi, Stefano; Anker, Daniela; Rosella, Laura

doi:10.1136/bmj.n2126

Cited by 11 publications

(6 citation statements)

References 4 publications

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“…The first and basic layer is a declaration and sentinel system to track new cases by healthcare providers, enabling control of local outbreaks and identification of new variants. Because cases diagnosed by healthcare providers are exposed to surveillance bias,3 the second layer should be repeated population based surveys, based on random sampling and using antigenic or PCR tests, to assess the proportion of people infected across time. This is the only way to have a reliable estimate of the dynamics of virus spread4: modelling is not enough.…”

mentioning

confidence: 99%

Covid-19: Surveillance systems for the new normal

Tancredi

Cullati

2022

BMJ

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mentioning

confidence: 99%

Covid-19: Surveillance systems for the new normal

Tancredi

Cullati

2022

BMJ

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“…The main limitation of this observational registry study is information and surveillance bias 68 . Attack rate estimation depends on the tests being performed, since contacts will be considered positive only if they were tested.…”

Section: Discussionmentioning

confidence: 98%

Effect of mRNA vaccination and previous infections on SARS-CoV-2 transmission across four variants: adjusted analysis of 111’432 declared contacts

Mongin

Bürgisser

Laurie

et al. 2023

Preprint

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The immunity conferred by SARS-CoV-2 vaccines and infections reduces the transmission of the virus. But it is not clear how the effect of immunity is shared between a reduction of the contagiousness and an increased protection against infection. To answer this question, we used a register of >50’000 SARS-CoV-2 positive index cases and their >110’000 declared contacts to estimate the association between secondary attack rate and immunity status (natural infection, vaccine, or both). Analyses were stratified per four SARS-Cov-2 variants and adjusted for index cases and contacts socio-demographic characteristics and the propensity of the contacts to be tested. The reduction of the propagation conferred by immunity was mainly a protection of the contacts against infection rather than a diminution of the contagiousness of the index cases. The largest immunity effect was conferred for both by natural infection, especially when recent for the contacts. Although of smaller amplitude, the effect of vaccination for index, i.e. the reduction of contagiousness, was less affected by SarS-CoV-2 variant and time since vaccination than the effect for contacts, i.e. the increase of protection against infection. Indeed, vaccination offered protection against infection only if given less than 6 months before and only for the variants preceding omicron, while the vaccination kept moderately reducing the index infectivity during the omicron wave, even when given more than 6 months ago. Hybrid immunity (vaccination and infection) did not have increased effectiveness than recent infection. These findings support the idea that vaccination also protects others, and highlight the need for the implementation of non-personal interventions reducing Sars-CoV-2 propagation, such as ventilation or air filtration.

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“…Symptomatic disease and infection outcomes are prone to underrepresentation due to surveillance bias resulting from factors such as reluctance to test for COVID-19. 52 Thirdly, this study only included peer-reviewed publications. It excluded some of the earliest evidence on inactivated vaccines, many of which were RCTs published as pre-prints for emergency approvals during the early stage of the pandemic.…”

Section: Discussionmentioning

confidence: 99%