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Tailing COVID-19 vaccines effectiveness with COVVAC SERO programme

Tailing COVID-19 vaccines effectiveness with COVVAC SERO programme
2022 03-17

The COVID-19 pandemic that started in 2020 is still causing a major health crisis around the world, reaching more than 400 million confirmed cases to date. Generally triggering mild symptoms that are usually associated with a common cold, the COVID-19 infection tends to increase in severity with age, especially amongst those above 60 years old, and those with pre-existing chronic diseases and conditions (hypertension, diabetes, obesity, cardio-respiratory diseases, etc).

By the end of 2020, we were counting on several new vaccines and mass vaccination programmes to tackle the pandemic evolution. In Luxembourg, 1 260 187 doses have been administered to date, representing 467 130 people who are completely vaccinated and 356 542 booster doses. As the vaccination effort continues, monitoring the effectiveness of this measure in the country, especially in a highly vulnerable population, is a key component to the surveillance and control of the epidemic.

The COVID-19 Vaccination and Serological Surveillance Programme (COVVAC SERO), conducted by the National Reference Laboratory for Acute Respiratory Infections at the LNS in partnership with the Health Directorate, aims to analyse the vaccines’ effectiveness in nursing homes in Luxembourg. In order to evaluate the effectiveness of SARS-CoV-2 vaccines (in the short, medium, and long term) in residents and staff of nursing homes in Luxembourg, the programme will follow, a cohort of residents and staff who have received at least one COVID-19 vaccine dose, during 18 months.

Through a questionnaire sent to each nursing home participant and the collection of serological samples, the COVVAC SERO programme intends to monitor the evolution of serological IgG antibody levels after vaccination,  identify potential prognostic factors associated with the immune response, and monitor vaccination breakthrough infections during the study’s follow-up period.

Daniel Alvarez, Epidemiologist at the LNS’ Microbiology department, tells us about how the  COVVAC SERO programme helps the monitoring of the COVID-19 pandemic: “The importance of the COVVAC SERO programme relies on its target population, the elderly in nursing homes, who have been severely impacted by the pandemic. Monitoring the elderly immune response after vaccination remains key to assuring enough protection to prevent further infections and hospitalisations.”


COVVAC SERO first and second phase

The first and second phases of the programme relied on 9439 participants who presented both a complete vaccine protocol and usable serological results. The index established with the Anti-SARS-CoV-2 ELISA IgG kit (EuroImmun) measured the level of specific IgG antibodies circulating in the blood of the participants in a semi-quantitative way.

Currently 5 vaccines are authorised in the European Union: Comirnaty (BioNTech-Pfizer, since 21 Dec 2020), Spikevax (Moderna, since 6 Jan 2021), Vaxzevria (AstraZeneca, since 29 Jan 2021), Janssen vaccine (Janssen-Cilag, since 11 March 2021) and, recently, Nuvaxovid (Novavax, since 20 Dec 2021). So far the programme has only measured the following vaccines: BioNTech-Pfizer, Moderna, AstraZeneca, and Janssen.  The results of the first and second surveillance phases show that all the vaccines monitored induce a detectable immune response.

Even though the antibody rate decreases significantly with time and age as well as differs according to the vaccines administered, the immune response seems globally satisfactory at the end of the vaccination protocol. These results will be monitored in the next phases of the programme, however, it seems to show the usefulness of a third booster dose. Furthermore, the evolution of the pandemic with the appearance of new variants such as Omicron will be taken into account.

The programme analysed the participants’ data such as the date of birth, sex, occupation, main comorbidity, weight, history of SARS-CoV-2 infection, number of vaccine doses, type of vaccine, dates of vaccination, in addition to their serological samples. The samples were collected using Dried Blood Spot (DBS) cards. Each serological test was performed using EUROIMMUN Anti-SARS-CoV-2 ELISA (IgG) and the statistical analyses were performed using R (R Core Team, 2021).

Data Protection: The Participants (staff and residents) received information concerning the processing of personal data by the LNS within the framework of the mission. The context of the mission is the public interest in the effectiveness of vaccines against SARS-CoV-2 (short, medium, and long term) in residents and staff of nursing homes in Luxembourg. The mission is invested in monitoring the vaccinated participants to access the immune response of the population against COVID-19. For more information about the processing of personal data, the participants could consult the following link: 


The context of the COVID-19 pandemic

According to the World Health Organization (WHO) the COVID-19 disease is characterised by a respiratory infection, including symptoms like fever, cough, fatigue, loss of taste or smell, but it can also aggravate with shortness of breath and pneumonia. According to the WHO, 15% of infections require oxygen support and 5% need intensive care. Case fatality rates worldwide range from 0.98% in the Western Pacific to 2.03% in Africa, although in some countries it is higher, like 6.13% in Peru or 3.35% in Bulgaria. In the Grand Duchy of Luxembourg, 178 507 cases have been confirmed as of 21 February 2022, of which 985 patients have died (case fatality rate of 0.55%).

A total of 10 407 359 583 doses of COVID-19 vaccines have been administered worldwide as of 21 February 2022, according to the WHO. The authorised vaccines in Europe have their safety constantly monitored by the European Medicines Agency (EMA) and other international institutions, while their effectiveness is assessed continuously as new data are available. COVID-19 vaccines have proven highly effective in protecting against severe disease, even with more recent virus variants like Omicron, while protection against infection and symptomatic disease is lower than observed with previous variants. In addition, evidence suggests that the effectiveness of these vaccines declines over time, especially in the elderly. For that reason, vaccination programmes now include booster doses, that have been observed to further improve the vaccine effectiveness.



World Health Organization. Weekly epidemiological update on COVID-19 – 8 February 2022. WHO, 2022. Accessed 22 February 2022 at:

World Health Organization. WHO Coronavirus (COVID-19) Dashboard. [Internet] Accessed 22 February 2022 at:

The Luxembourgish data platform. COVID-19: Rapports journaliers. Ministère de la Santé, 2022. Accessed 22 February 2022 at:

European Medicines Agency. COVID-19 vaccines: authorised. [Internet] Accessed 22 February 2022 at: