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Conducted on a total of 10,223 participants

Second study on seroprevalence in Spain updates information on vaccine-preventable diseases and other infections

Friday 9 April 2021

A team from the Carlos III Institute of Health (Spanish acronym: ISCIII) took part in conducting the 2nd Study on Seroprevalence in Spain, which was coordinated by the Directorate-General of Public Health of the Ministry of Health and reviews the situation regarding immuno-preventable diseases (i.e., those that can be prevented with the use of vaccines).

The report, which is being published 21 years after the first, supports the ongoing assessment of these diseases and provides broader knowledge about the real immunity status of the Spanish population against them. The report also includes a study on the prevalence of naturally acquired immunity against other infectious agents of relevance to public health.

The goal of the research reflected by the results in the report is to estimate the prevalence of antibodies against various pathologies in the population aged 2-80 residing in Spain. The diseases included in the study were poliomyelitis, diphtheria, tetanus, whooping cough, measles, rubella, mumps, chickenpox, serogroup C invasive meningococcal disease, hepatitis A, B, C, D and E, and infection by human immunodeficiency virus (HIV).

The teams from the ISCIII that took part in drawing up the report belong to the National Microbiology Centre (coordinated by Julio Vázquez) and the National Epidemiology Centre (coordinated by Josefa Masa). From the National Microbiology Centre, the Hepatitis Unit (Ana Avellón), the Serology Lab (Fernando de Ory and Mayte Pérez) and the Neisseria Unit (Raquel Abad) took part in this project. Under coordination by the Ministry of Health, the regional government authorities (via a specific work group) and numerous health centres throughout Spain also took part in the study.

The study, which involved a total of 10,223 participants, provides a snapshot of immunity status in different age groups and genders against the listed diseases and the vaccination coverage by age group in people under-30. The goal is to know whether immunity in this population is in line with the vaccines administered according to the current vaccination schedule at any given time.

Furthermore, it enables an estimation of the prevalence of infection by micro-organisms of interest to public health, an analysis of changes taking place over time in the prevalence of the diseases included in the survey and investigation of the factors associated with immunity status against each one of the diseases included in the study.

Finally, the data gathered in the study enabled a collection of serum samples to be created for subsequent research on transmissible diseases of interest to public health.

By disease, the main conclusions reached by the study were as follows:


A decline is observed in the population with protective antibody titres between the 10-15 years age group and the 30-39 years age group. This decrease is more pronounced in the 20-29 years age group, which may be due to the loss of serological protection over time following vaccination with the second dose. A recommendation is made to assess the need for new vaccination strategies in the medium and long term in certain population groups based on their likelihood of exposure.


Immunity in the population stands at over 95% in all age groups (higher among women), which demonstrates maintenance of the immunity produced through vaccination even when provided during childhood. This high level of immunity in the population guarantees the ongoing elimination of rubella in Spain.


The seroprevalence of antibodies against mumps is high among those aged 2-14 years of age. Immunity begins to fall after this age group and increases again in those over-30. On the one hand, this suggests a loss of immunity over time following vaccination and, on the other hand, the improved persistence of immunity following natural infection in age groups born before 1978.


The prevalence of neutralising antibodies against poliovirus types 1 and 3 is very high in all age groups, which guarantees the susceptible population level of less than 15% necessary to prevent transmission in the event of introduction of this virus. These data guarantee compliance with the population immunity target for contributing towards the eradication of this disease.


The seroprevalence of protective antibodies against this disease increases with age up to 30, after which there is a significant decrease that is probably due to the loss of immunity over time. The evidence suggests that high childhood vaccination coverage rates help to limit secondary transmission and the maintenance of transmission chains throughout the population following imported cases. Furthermore, improving vaccination against tetanus with combined vaccines against tetanus and diphtheria (Td) in the older population could help to also improve immunity against diphtheria.


There is a high prevalence of protective levels of antibodies against tetanus in the over-50s, which falls significantly from this age group upwards, especially in the over-60s. The report believes it is important to raise awareness among the general population and the healthcare community about the need to vaccinate the elderly, a population group that contains a significant proportion of susceptible people.

Whooping cough

The seroprevalence results indicate that the Bordetella pertussis micro-organism is circulating in all age groups.


Introduction of this vaccine into the vaccination schedule is reflected in an increase in seroprevalence of antibodies in the youngest age group (2-5 years) when compared with previous studies. The report indicates that it is still too soon to observe the effect of childhood vaccination in other age groups.

Invasive meningococcal disease (serogroup C)

The seroprevalence of protective antibodies against Serogroup C IMD is close on 75% in age groups that have benefited from systemic vaccination in adolescence (12-16 years). Furthermore, longer-lasting immunity and greater protection is seen in these age groups.

Hepatitis A

A high proportion of susceptible individuals is observed in the general population. However, almost 5% of the child population aged 2-5 presents immunity that is maintained until 19 years of age, meaning it was probably acquired following natural exposure to HAV during early childhood.

This situation of infection by the hepatitis A virus during childhood, combined with the increased susceptibility in the adult population, clearly demonstrates the importance of epidemiological surveillance in the identification of cases and in swift action against outbreaks in order to limit the possible spread.

Hepatitis B and D

The prevalence of infection by the hepatitis B virus has fallen significantly since the previous study was conducted in 1996. The prevalence of active infection by the hepatitis B virus and of women carrying antibodies is also very low. The prevalence of hepatitis D in carriers of antibodies is similar to that seen in other studies.

Furthermore, the seroprevalence of antibodies against hepatitis B shows two peaks. This reflects the systemic vaccination carried out in Spain that began in adolescents and was subsequently switched to children. All these results reflect the success of the hepatitis B vaccination programme.

Hepatitis C

The level of infection prevalence in Spain is low, especially in terms of active infection prevalence. Prevalence is higher among men and among people born outside of Spain.

Hepatitis E

The results on seroprevalence of antibodies against this virus are higher than the estimates made until now in Spain and suggest ongoing transmission with greater exposure in the past. Antibody persistence is observed in those who have been exposed to the virus. The low number of acute infection cases that were identified seems to indicate that infection goes unnoticed in its sub-clinical and asymptomatic states.

HIV infection

The overall prevalence of HIV infection obtained in this study is lower than other estimates made, which might be due to the characteristics of the population studied and the lower representation of more exposed population groups. Based on age and gender, as well as the undiagnosed fraction, prevalence remains within the range of other estimates made.

A summary of the results in this report was also published in the Spanish Public Health Magazine. The full text will be passed on to scientific bodies and other interested stakeholders.

Non official translation