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Assessing the Prevalence of Antibodies Against the SARS-CoV-2

Cendea de Cizur
Photo: ISGlobal - Volunteers and fieldwork coordinators for the Cendea de Cizur seroprevalence survey

[Authors: Uxue Alfonso Viguria, Global Health student at University of Geneva and Marta Ribes Agost, ISGlobal-UB Global Health Master student 2019-2020]

As World Health Organisation Director-General Tedros Adhanom declared during a press conference on COVID-19: “We need to [...] bring our best science to the forefront to find shared answers to shared problems.” The Barcelona Institute for Global Health (ISGlobal) has joined this global race against time.

Among other activities related to COVID-19, ISGlobal has undertaken a seroprevalence survey in Cendea de Cizur, a municipality in Spain’s Navarre region. The study, led by ISGlobal researcher Carlos Chaccour, is supported by the Cendea de Cizur town council and the University of Navarre’s Centre for Applied Medical Research (CIMA). The main objective is to determine the prevalence of antibodies against the SARS-CoV-2 virus.

The survey aims to answer some of the key questions that have emerged during the pandemic: How does the novel coronavirus affect different age groups, and children in particular? What percentage of people who have had the virus were not diagnosed at the time of infection? Who is at the highest risk of contracting the disease?

Thanks to the National Sero-Epidemiological Survey, we know that the estimated prevalence of IgG antibodies —that is, antibodies indicating past infection—is about 5% in Spain as a whole and around one percentage point lower in minors. The latest data from that study show that 87.6% of people who tested positive for the virus at least two weeks earlier have IgG antibodies and around one third of infections have been asymptomatic.

Another ISGlobal study conducted in early March found that 11.2% of health care workers at Barcelona’s Hospital Clínic had been infected with the virus, compared with only 1.6% of workers at a hospital in Germany at the end of April. In Italy’s hard-hit Lombardy region, it was calculated that 28% of the population had been exposed to the virus by early April, while a population-based study in Geneva estimated a seroprevalence rate of 10.8% in the first week of May. This disparity of outcomes suggests that the rate of spread may vary greatly depending on the context. The new study in Cendea de Cizur aims to provide more granular, context-specific data to complement the nationwide survey.

The fieldwork team consisted of 14 volunteers, all students or recent graduates in health-related disciplines at the University of Navarre. In one way or another, all of the volunteers had been affected academically by COVID-19. By working on this study, they were able to continue their training while contributing to the response to the pandemic.

The fieldwork team consisted of 14 volunteers, all students or recent graduates in health-related disciplines at the University of Navarre

As the volunteers explain in the video, after a few days of training, they hit the streets equipped with vests, backpacks and sample kits to visit the homes of 742 study participants. They managed to collect data and samples from every last one of them in just one week. The work schedule was intense—from early morning to late afternoon, with barely any time to eat or take a break. The moments between visits provided the only respite. Once inside people’s homes, the volunteers asked survey questions that unleashed all sorts of quarantine stories. Young children proudly showed off their “school” on computer screens, while older people often lamented not being able to see their grandchildren.


Day by day, the volunteers perfected the technique of collecting capillary blood samples and mastered the art of explaining and obtaining informed consent. Through their hard work and enthusiasm, they helped to make the study a success. For many of these dedicated volunteers, it was their first foray into the world of scientific research.

The collected samples will be analysed by ISGlobal’s immunology team, led by Research Professor Carlota Dobaño

The collected samples will be analysed by ISGlobal’s immunology team, led by Research Professor Carlota Dobaño. Levels of IgG, IgM and IgA antibodies against SARS-CoV-2 will be determined using a method based on quantitative suspension array technology developed by Dobaño’s team at the Esther Koplowitz Centre (CEK). The results of the study will be published in the coming weeks.

None of this would have been possible without the hard work of the volunteers (Ainhoa Ezcurra, Ane Etxepeteleku, Camino Esparza, Diego Ozcoidi, Fernando Gárate, Íñigo Cumba, Irene Colomo, Isabel Blavia, Leyre Jiménez, Lucía Durán, Nuria Goñi, Patricia Oficialdegui, Sophie Bernard and Virginia Orillo); the coordination of ISGlobal researchers Júlia Montañà, Patricia Nicolás and the authors of this post (Marta and Uxue); and the collaboration of the CIMA Biobank.