Rubella is an infectious disease caused by an RNA virus belonging to the Togaviridae family. The only reservoir of infection is in humans and the infectious agent is most frequently spread from patients to healthy people by aerosol. Vertical transmission of the virus and intrauterine infection of the foetus is possible in pregnant women and especially during the first trimester of pregnancy, (1 - 3). Rubella presents a risk in both manifest and asymptomatic forms. In 25-50% of cases the infection is asymptomatic (3). The course of disease is usually mild. However, in the Russian Federation during periods with increased incidence, a rise in the number of cases of rubella meningoencephalitis with the development of brain oedema among children was observed (4). One of the most frequent reasons for miscarriage, low birth-weight and death among small children is congenital general viral infections and, in 86% of the cases with mixed etiology, rubella infection is the primary cause (5). In the case of intrauterine rubella virus infection of the foetus, many developmental defects occur. In some territories of the Russian Federation defects due to rubella infection constitute up to 15% of all birth anomalies (6).
Due to the particular etiology and epidemiology of rubella, vaccine prophylaxis for this infection was introduced in the USA during the 1960s, in a number of European countries at the beginning of the 1980s, and in Russia from 1998 (6 - 9). In Russia, rubella has been officially registered since 1979, congenital rubella since 1991. An organisational-methodological background for a system of epidemiological surveillance of this disease has been developed (1, 2, 6, 10). The WHO European Regional Office has taken on the task of reducing the incidence of congenital rubella to less than 1 in 100,000 live births by 2010 (3).
The objective of this study was to study the herd immunity and to judge the effectiveness of immunization against rubella in the city of Naryan-Mar, Nenets Autonomous Okrug in Russia.
Materials and Methods
Serum samples from 100 persons in two age groups of both genders were tested for rubella virus antibodies. Spesific rubella virus IgG was detected using a rapid enzyme immunoassay. If the spot on the “tooth” of the test comb changed colour, a semi quantitative interpretation of the colour intensity was made by comparing the test spot with the standard calibrated colour scale for the titre of the antibodies in serum. When no antibodies were present in the sera, the lower part of the “tooth” remained uncoloured. Antibodies in titres of 1:30 and higher were considered to be protective and 1:15 represented a marginal value. Blood samples from vaccinated children were collected from those who had been immunized more than half a year earlier. None of the persons examined had acute illnesses (including acute respiratory diseases) and none were known to have had recurrences of chronic diseases during the two months prior to sample collection.
Information concerning vaccination history and rubella infection was obtained from out-patient cards. In the majority of cases, rubella diagnosis is based on clinical observation in the Russian Federation (including the Nenets Autonomous Okrug).
At the end of 2003, 100 children and young people (61 children from 2-4 years of age and 39 youths from 13-15 years of age) in Naryan-Mar were examined for presence of rubella virus antibodies. There were 30 boys (49%) and 31 girls in the first group, and 22 (56%) male and 17 female teenagers in the second group.
In total, rubella virus antibodies were detected in 89 of the 100 examined persons (89%). The geometric mean titre was 53. Among the children rubella virus antibodies were detected in 56 of 61 samples (92%). The geometric mean titre was 44. Among teenagers rubella virus antibodies were detected in 33 of 39 samples (85%). The geometric mean titre was 74.
Fifty eight of 61 (97%) children had been vaccinated against rubella. The three unvaccinated children had no antibodies to rubella. Among the 58 children who had been vaccinated during the six months prior to examination, 45 (78%) had antibody levels considered to be protective and 11 children (19%) had rubella virus antibodies at marginal values. The geometric mean titre was 44. In two vaccinated children rubella virus antbodies were not detected.
Among the 39 teenagers, 15 (39%) had been vaccinated against rubella and had antibodies at protective concentrations. The geometric mean titre was 76. Among the 24 unvaccinated teenagers, antibodies at protective titres were detected in 18 persons (75%). The geometric mean titre was 73. Rubella antibodies were not detected in the remaining six unvaccinated teenagers.
In total, 73 children and teenagers (73% of all those examined) were vaccinated. Rubella virus antibodies were detected in 60 persons (82%) at protective titres and in 11 (15%) at marginal titres. Two vaccinees lacked rubella virus antibodies. The geometric mean titre was 49.
Among both groups, 27 persons (27%) had not been vaccinated against rubella. Antibodies were detected in 18 unvaccinated persons at protective titres (67%). The geometric mean titre was 73. In this group, 11 persons (41%) had the diagnosis “rubella” in their medical history. Among those who had had rubella, specific antibodies were detected in nine persons (82%) at protective titres. The geometric mean titre was 70. In the group of unvaccinated who did not have rubella in the anamnesis, nine (56%) had specific antibodies at protective titres. The geometric mean titre was 76.
A high level of protection against rubella was found in the examined group of children and teenagers from Naryan-Mar, Nenets Autonomous Okrug. Among the children in the younger age group of whom the majority were vaccinated against rubella, the level of collective immunity was higher in comparison to teenagers. While only approximately half of the teenagers had been vaccinated, they were more likely to have had rubella as a result of circulating rubella virus than the children. In addition, the geometric mean antibody titre was higher among teenagers than among children. A similar situation was observed when examining the level of post-vaccination immunity in both groups. The geometric mean antibody titre in the group of vaccinated teenagers was higher than in the group of younger children. Such differences may be caused by true difference in intentensity of the immune response to the vaccine against rubella in persons of the two groups, and also by the fact that many teenagers may have had antibodies to rubella as a result of rubella infection prior to vaccination. It was shown that all vaccinated teenagers had rubella virus antibodies while antibodies were detected in only 75% of the unvaccinated persons examined.
The effectiveness of the vaccine prevention in both groups taken together was more than 97%, which is in accordance with the clinical protection offered by vaccination against rubella. However, rubella antibody titres were at marginal levels in 15% of the vaccinees while two thirds of the unvaccinated persons had protective antibody levels. The geometric mean titre in the group of vaccinated was considerably lower than among persons who had not been vaccinated against rubella. This probably reflects a large number of persons who had experienced asymptomatic rubella (33%) and thus had specific antibodies but had not been diagnosed with rubella. In contrast, a number of persons who had been diagnosed with rubella but did not have specific antibodies may indicate possible errors in the clinical diagnosis of rubella infection.
It is of great concern that 25% of unvaccinated teenagers had no protection against rubella. With the high level of vaccine protection among children, it is reasonable to assume that circulating rubella virus will become rare in Naryan-Mar and thus reduce the likelihood that teenagers will be exposed to the virus. Consequently, teenage girls may in a few years be at risk of acquiring rubella during pregnancy. We therefore recommend that teenage girls be vaccinated against rubella.
The authors express sincere thanks to the Norwegian Institute of Public Health, Department of Infectious Disease Epidemiology and especially to Preben Aavitsland and Stein Andresen for professional and financial support in the implementation of the project and preparation of this article.
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