Sero-prevalence of SARS-CoV-2 antibodies in blood donors during the third wave of infection in Norway, winter/spring 2021

Marte Hvalryg,Lise Sofie H Nissen-Meyer

doi:10.1016/j.transci.2021.103256

Marte Hvalryg, Lise Sofie H Nissen-Meyer

Open Access

https://doi.org/10.1016/j.transci.2021.103256

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Abstract

Cross-sectional studies of the prevalence of anti-SARS-CoV-2 in representative groups are routinely used for surveillance of public health in Norway. The group of blood donors is easily accessible to provide an estimate over the infection prevalence. Repeated testing of returning donors also generates data about the duration of the antibody response following infection and vaccination.The aim of the current study was to provide updated information about the development of the pandemic in the blood donor population, and to estimate the number of asymptomatic donors visiting the blood center, in an effort to evaluate the measures to prevent virus spreading between donors and staff.In the two main blood banks in the Oslo area, all blood donors were offered antibody testing for a period of three months. Almost 12,000 donors were tested, and the mean weekly prevalence of antibody positive donors due to infection was 2.7 % (varied from 2.1 to 4.0 %). The number of donors presenting following vaccination was 810 (6.9 %). An average of 38 % of the infections had been asymptomatic, and 31 % of the antibody-positive donors were unaware of having been infected.In conclusion, the proportion of blood donors seropositive for anti-SARS-CoV-2 in our blood centers was stable whereas the number of vaccinated blood donors rapidly increased. This indicates that the virus spreading in the third wave of infection in the Oslo area mainly happened in groups underrepresented as blood donors. Health care workers prioritized for early vaccination may be overrepresented in the study period.

Highlights

The SARS-CoV-2 pandemic has exhibited diverse characteristics in different communities, and such epidemiological aspects of different countries and population groups have necessitated a plethora of infec tion surveillance studies
Considering that a number of health workers are blood donors, we added to the questionnaire a question whether they had received the vaccine or not. This project aimed to provide updated information about the virus spread in the blood donor group, with some relevance to the general population, and to calculate the number of asymptomatic do nors coming to the blood center
In a study of 1,912 residual sera from Norwegian microbiology lab oratories collected in January 2021, the sero-prevalence in the Norwe gian population was estimated to 3.2 % [15]

Summary

Introduction

The SARS-CoV-2 pandemic has exhibited diverse characteristics in different communities, and such epidemiological aspects of different countries and population groups have necessitated a plethora of infec tion surveillance studies. In Norway, the Institute of Public Health per formed infection surveillance through weekly testing of randomly selected individuals belonging to previously established study groups in the Oslo area from week 18-50/2020 [1]. Antibody seroprevalence studies in blood donors contribute naturally to the data collection, and have been used in a number of countries [2,3,4,5]. In Denmark, continuous antibody screening of all donors is being used to estimate the number of asymp tomatic and undiagnosed cases [6]. Practical procedures to protect both donors and staff implies increased work load and psychosocial stress in the personnel group, and have to be balanced against the risk of infection at a given time [7]

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