Rubella Seropositivity in Pregnant Women After Vaccination Campaign in Brazil's Federal District

Abstract

Rubella is an acute viral disease that usually does not generate sequels; however, in pregnant women the infection can cause serious abnormalities to fetuses, which are collectively called congenital rubella syndrome. In Brazil, population immunization was started in 1992, but few epidemiological studies have been conducted to assess vaccination coverage and seroconversion since then. The aim of this work is to evaluate the seropositivity of pregnant women to rubella virus after vaccination campaign was carried out in 2008. Serological tests for rubella diagnosis were performed in 87 pregnant women who attended the University of Brasilia Hospital, Federal District, Brazil. Antirubella IgG antibodies were detected in 83 out of 87 pregnant women (95.4%), with an age-independent seroprevalence. Only one woman was positive in IgM serological tests. Our data suggest high levels of vaccination coverage and antirubella immunization in the Brazil Federal District population.

Introduction

Rubella, also known as “German measles,” is an acute viral disease characterized by fever and papular rash. In most cases, the disease is mild, self-limited, and usually does not generate sequels (2). However, in pregnant women the infection can cause serious abnormalities to the fetus, including deafness, blindness, heart defects, and mental retardation, which are collectively called congenital rubella syndrome (CRS) (3,14). An increased risk of developmental disorders is observed if the infection occurs during the first 12 weeks of pregnancy.

Rubella vaccine is a successful prophylactic measure, controlling virus dissemination and CRS worldwide (13). In Brazil, population immunization was started in 1992 with a combined vaccine for measles, mumps, and rubella (MMR), which was gradually implemented in all states until 2000. In 2003, this vaccine was included in the National Immunization Schedule, with a dose given at 12–15 months of age and a booster at 4–6 years of age (17).

MMR implementation had changed the epidemiological scenario of rubella in Brazil. In the late 1990s, rubella incidence reached 15:100,000 in children aged 1–9 years and 13:100,000 in age group 15–29 years. After the vaccination campaigns, in 2006, the incidence decreased to 1:100,000 in the general population. So, the disease could not be considered eradicated because CRS cases are still been detected (1,5). Given this situation, the members of the World Health Organization and the Pan American Health Organization (7,13) established the deadline to eliminate rubella and CRS in Americas by the year 2010.

To meet that goal, Brazil has introduced national MMR routine immunization of children and young adults to achieve high immunization coverage (95%) of the population (11,12). In 2008, a national campaign to eliminate rubella and CRS was launched in the country, targeting 69 million adolescents and adults. Although vaccination campaign has obtained great support and acceptability of the population, few epidemiological studies have been conducted to assess vaccination coverage and seroconversion (17,19). Titers of IgG and IgM antirubella virus antibodies are the main methodology to confirm vaccine effectiveness (19).

After MMR vaccination, IgG titers are generally higher than 10 IU/mL, indicating seroconversion and enduring vaccine protection lifelong (15). Absence of antibodies, as well as low titers (<10 IU/mL), indicates susceptibility to disease. Greater attention should be given to positive IgM results because false positive may appear in consequence of cross-reactions with other agents, such as rheumatoid factor, EB19, and Epstein Barr virus (EB19). In this situation, it is recommended to carry out an immunocapture test for IgM antibodies (15).

In this context, the aim of this work was to evaluate the seropositivity of pregnant women to rubella virus after vaccination campaign was carried out in 2008.

Materials and Methods

Ethical statement and study population

The research protocol was approved by the Ethical Committee on Human Research of Brasília University (protocol number 048/12).

It is a retrospective study conducted from January to December 2010 in the Clinical Pathology Laboratory of the University of Brasilia Hospital (HUB). HUB accepts patients from all surrounding areas of Brazil's Federal District, considered a representative portion of its total population. The study population included pregnant women, from 15 to 50 years old, countersigned by the hospital gynecology clinic that performed serologic tests for the diagnosis of congenital infections. During this period, 87 pregnant women underwent prenatal examinations with medical request to perform rubella serology.

Serological tests

All serum samples were tested for rubella using commercial kit Diasorin^® (Saluggia, Italy). An indirect chemiluminescence immunoassay (CLIA) using magnetic microparticles for quantitative determination of IgG (kit number 310720) and IgM (kit number 310730) antibodies antirubella virus was employed. Antibodies titers were expressed in international units per mL (IU/mL) to rubella IgG and arbitrary units per mL (AU/mL) to rubella IgM. Samples were processed according to manufacturer's instructions. Positive and inconclusive IgM tests were confirmed using the enzyme linked fluorescent assay (ELFA) methodology (MiniVidas^®, BioMerièux, Brazil). Results of serological tests were classified as positive (rubella IgG ≥10 IU/mL; rubella IgM ≥25 AU/mL), negative (rubella IgG <10 IU/mL; rubella IgM <20 AU/mL), or inconclusive (20 ≤ IgM ≤ 25 AU/mL).

Statistical analysis

The programs Statistical Package for the Social Sciences (SPSS version 17, Chicago Incorporation) and Microsoft Office Excel 2010 were used for statistical analysis. The McNemar and Kruskal–Wallis tests were used for experimental data analysis, with 95% of confidence interval. The level of significance selected was p-value <0.05.

Results

Rubella antibodies detection

Of the 87 tested samples, CLIA identified antirubella IgG antibodies in 83 pregnant women, corresponding to a specific IgG seropositivity of 95.4% (Table 1). When we evaluated results for IgM serology, 85 women (97.7%) tested negative and 1 (1.1%) had inconclusive antibodies title. Only one (1.1%) woman was positive for IgM and IgG, whereas four women (4.6%) were negative in both tests. Interestingly, IgG seropositivity was observed regardless of age. However, IgM seroprevalence of age group 36–50 years was statistically different from the others (p = 0.0034). Positive and inconclusive IgM tests were confirmed using ELFA methodology and the results were in agreement with those performed by CLIA.

Table 1.

Rubella Seropositivity According to Age

		Rubella
		IgG		IgM
Age group (years old)	Samples	Positive (≥10 IU/mL)	Negative (<10 IU/mL)	Positive (≥25 AU/mL)	Negative (<20 AU/mL)	Inconclusive (20 ≤ IgM ≤ 25)
<18	5	4 (80.0)	1 (20.0)	0 (0.0)	5 (100.0)	0 (0.0)
18–25	19	19 (100.0)	0 (0.0)	0 (0.0)	19 (100.0)	0 (0.0)
26–35	57	54 (94.7)	3 (5.3)	0 (0.0)	56 (98.2)	1 (1.8)
36–50	6	6 (100.0)	0 (0.0)	1 (16.7)	5 (83.3)	0 (0.0)
Total	87	83 (95.4)	4 (4.6)	1 (1.1)	85 (97.7)	1 (1.1)

Data in parentheses represent the percentages.

Table 2 shows the mean and standard deviation of antirubella IgG titers according to age. Antibody rates were higher in groups 18–25 and 26–35 years old, reaching 71 IU/mL. However, no statistically significant differences were found.

Table 2.

Antibody Titers in Pregnant Women

Rubella
		Titers (IU/mL)
Age groups (years old)	Samples	Mean	SD
<18	4	26.0	13.7
18–25	19	71.2	77.6
26–35	54	71.3	79.5
36–50	6	36.9	20.4

SD, standard deviation.

Discussion

Rubella is a common infection worldwide, but introduction of mass vaccination changed this scenario. As a goal for rubella eradication, WHO had established the year 2010 as a deadline for complete elimination of the virus in the Americas. Successfully, Brazil registered the interruption of virus transmission and CRS cases in 2009 (12). However, only in 2015 the disease was considered abrogated throughout the continent. Isolated cases of this infection are still been reported in Argentina, Canada, and the United States (6,10).

Considering the prevalence of rubella in Brazil is about 1:100,000 and that the population of the Federal District is representative of the overall Brazilian population, very low rates of positivity were expected, which did not occur in our study. The high positivity of antirubella IgG antibody in pregnant women (95.4%), with only 4.6% patients vulnerable to infection, suggests high levels of vaccination coverage and immunization in the Brazil Federal District population (9). Importantly, rubella antigen-containing vaccines provide lifelong immunity. The low susceptibility to disease after vaccination campaigns corroborates with other works performed in Brazil (16,18) and resembles data found in several countries, such as Spain (20), Italy (8), Japan (21), and the United Kingdom (4), where the proportion of pregnant women susceptible to rubella is <10%.

Only one pregnant woman (age group 36–50 years) showed antirubella IgM antibody rates >25 AU/mL. This result may represent the existence of individuals who were not contemplated in vaccination campaigns that took place from 1990s onward. Fortunately, no other pregnant woman had IgM positivity, an indicator of the acute phase of the disease, demonstrating that vaccination campaigns are efficient, contributing to block virus transmission, including patients in the age group most susceptible to acquiring the infection. These data suggest that the risk of rubella outbreak in Brazil Federal District is low.

However, it is important to mention as a limitation of our work that women who did not attempt medical attention during the first trimester of pregnancy or during all periods of pregnancy could introduce a selection bias. Another limitation is the sample size, which, although small, is relevant considering this being the only study in Brazil's Federal District.

Large-scale antirubella vaccination campaigns contribute to decline rubella incidence and consequently the impacts of the infection during pregnancy. The maintenance of vaccination campaigns is essential to avoid future outbreaks.

Footnotes

Acknowledgment

We thank the patients who participated in this study.

Author Disclosure Statement

No competing financial interests exist.

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