Measles and rubella incidence in Arkhangelsk oblast during the period of mass vaccination was analysed. Only sporadic cases of measles have been registered in the oblast during the last decade and no cases of rubella have been reported since 2007. The routine immunization of the population against rubella brought about changes in the age structure of patients: people over 14 years of age are involved in the epidemic process. The vaccination campaign that was implemented 9 years ago has resulted in a decrease of rubella incidence that is now less than 1 case per 100,000 population.
The World Health Organization (WHO) developed and implemented a programme on the prevention of measles and congenital rubella. The major goal of the programme was to eliminate these infections by 2010 (1). The eradication plans have a profound theoretic basis, the relevance of which is beyond any doubt (2).
The measles eradication programme in the Russian Federation was divided into 3 stages (3). The first stage (2002-2004) was targeted at stabilizing measles incidence at a sporadic level in all regions of Russia. At the second stage (2005-2007) conditions were created for preventing new cases of measles and for complete eradication of the infection in Russia. Finally, the third stage (2008-2010) of the programme was required to collect and compile documents confirming the status of federal territories as areas free of domestically acquired measles.
Rubella was also included in the elimination program. For many years rubella was considered to be “the most harmless” child disease. However, later it was determined that rubella causes congenital foetal malformations (4). The only method of control over congenital rubella and its severe complications is prevention of acquired rubella through immunization (5,6). That is why WHO determined that the incidence of congenital rubella should be reduced to less than 1 case per 100,000 live-born children and the incidence of acquired rubella to less than 1 case per 100,000 population by the year 2010 (1,7). The total elimination of the rubella virus in the human population can be achieved by combination of the two-stage vaccination of children at the age of 12-16 months and 6 years, and the vaccination of teenage girls who previously (no less than 6 months prior) received only one dose of the vaccine as well as women of childbearing age (8). The long-term dynamics of measles and rubella incidence within the period of elimination helps to estimate the efficiency of immunization programmes.
Our study analyses the incidence of measles and rubella during the period of mass vaccination against these infections.
Arkhangelsk oblast is located in the north of European Russia. The oblast lies along the coast of three seas of the Arctic Ocean known for its bitter coldness: the White Sea, the Barents Sea and the Kara Sea. The coast line is about 3 thousand kilometres long. The oblast includes the Nenets Autonomous okrug, 20 administrative districts, 14 cities, 38 workers’ settlements and about 4 thousand rural settlements. The administrative centre of the oblast is Arkhangelsk. Other major cities of the oblast include Severodvinsk, Kotlas, Novodvinsk and Koryazhma. The area of the oblast is 587.4 thousand square kilometres (9).
The incidence of rubella and measles in Arkhangelsk oblast was analysed using the state statistical report forms: Form No.2 “Information on Infectious and Parasitic Diseases”, Form No.5 “Information on Preventive Vaccination” and Form No.6 “Information on Cohorts of Children, Teenagers and Adults Vaccinated Against Infectious Diseases”. Incidence data for rubella and measles in the Russian Federation were taken from published statistical and analytical materials of the Federal Service for Surveillance on Consumer Rights Protection and Human Well-Being (Rospotrebnadzor).
The epidemiological data were analysed using descriptive statistics. The data were summarized as medians (Мd), and 25th and 75th percentiles. The groups were compared using non-parametric Mann-Whitney test (U). The level of statistical significance was set at 0.05.
Since the 1990s, the epidemic process for measles in Russia has been characterized by a steady decline of the disease incidence. The highest incidences were registered in 1993 and 1999 with 12.9 and 10.7 cases per 100,000 population, respectively. Later, the incidence decreased drastically. From 1995 the measles incidence in the Russian Federation has remained low (Figure 1). For the last decade, only sporadic cases of the disease have been registered in Arkhangelsk oblast. In 2006, the measles incidence was 0.1 per 100,000 population, with one case of measles imported into the oblast by an adult. In 2007-2009, no new cases of measles were registered.
Fig. 1. Measles incidence dynamics in Arkhangelsk oblast and in the Russian Federation in 1993-2009
The analysis of measles incidence among children under the age of 14 also shows a decline in the disease incidence from 4.7 in 1995 to 0.4 in 2003. The highest incidence was registered in 1999 with 13.8 per 100,000 children under the age of 14 (Figure 2). In 2003 the last case of measles was registered in the oblast: the patient was an unvaccinated child under the age of 1 year. The diagnosis was confirmed by the enzyme immunoassay (EIA) method in the laboratory of the Regional Centre for Surveillance over Measles Infection (at the Research Institute of Epidemiology and Microbiology named after L. Pasteur in St. Petersburg). Since 2004 no new cases of measles have been registered among children under the age of 14. In the Russian Federation, the incidence of measles among children under the age of 14 was higher; 3.5 in 2004, 0.32 in 2005, 1.06 in 2006 and 0.15 in 2007 per 100,000 children under the age of 14.
Fig. 2. Measles incidence dynamics among children under the age of 14 in Arkhangelsk oblast in 1995-2009
The analysis of age structure is difficult to perform because the number of patients is quite small. In general, the share of adults among patients has started to increase in recent years (Figure 3). Measles cases among adults were registered before 2001 and one case was registered in 2006.
Fig. 3. Age structure of patients with measles in Arkhangelsk oblast in 1998 – 2009
The herd immunity against the infection is indirectly characterized by the immunization coverage of child population, the level of which in the Russian Federation in 2002 for the first time reached 95% (10). Since 1999 in Arkhangelsk oblast the immunization coverage of children at the age of 24 months against measles has either remained equal to or exceeded 95%. In 2009 the coverage reached 98.6%. The coverage of 6 year old children by booster vaccination against measles has also increased gradually from 47.7% in 1998 to 95.1% in 2003. The recommended level of coverage by booster vaccination against measles in the oblast was reached for the first time in 2003. In 2009 the booster vaccination coverage of 6 year old children was as high as 97.6%.
The epidemic dynamics of rubella was investigated using data collected in 1979-2009. The epidemic process of rubella can be divided into two periods: pre-vaccinal and vaccinal. The pre-vaccinal period lasted from 1979 to 1999; the vaccinal period started in 2000 and continued to 2009. During the pre-vaccinal period, the epidemic process was characterized by periodic rises and falls of the incidence, which demonstrated a lack of control over rubella infection. During the entire pre-vaccinal period, the incidence in Arkhangelsk oblast was higher than the average incidence in Russia, with the exception of a few years (1987, 1994 and 1997). In the period of vaccination against rubella, the infection incidence in the oblast started to decrease and in 2008-2009 it reached the value recommended by WHO, less than 1 case per 100,000 population.
During the pre-vaccinal period the mean long-term incidence of rubella in our region was 279.0 (180.9-429.9) per 100,000 population, while during the vaccinal period it was 59.7 (18.5-161.1) per 100,000 population (p=0.001). For the Russian Federation in general, the pre-vaccinal mean long-term incidence of rubella was 190.0 (141.0-273.1) and the vaccinal period was 100.4 (17.0-255.6) per 100,000 population. Thus, in the pre-vaccinal period, the mean long-term incidence of rubella in Arkhangelsk oblast was higher than in Russia (p=0.03). During the period of active immunization the mean long-term incidence of rubella in the oblast and in the Russian Federation became equal (p=0.6).
The epidemic process for the long-term dynamics of rubella incidence among the total population and children under the age of 14 in Arkhangelsk oblast showed mostly the same tendencies as in the Russian Federation in general (Figure 4). Before 1999 we could not find the incidence data for rubella among children in the Russian Federation.
Fig. 4. Dynamics of rubella incidence (per 100,000 population) among children under the age of 14 and among the whole population of Arkhangelsk oblast and the Russian Federation in 1995-2009
The mass vaccination against rubella in Arkhangelsk oblast not only helped to reduce the disease incidence, but also changed the age structure of patients. Prior to immunization, most of patients with rubella were children from 3 to 14 years of age. The share of children under the age of 3 was quite low and varied from 10.1 to 17.2% among children under the age of 14. This can be explained by the fact that younger children have fewer contacts with the environment and people. In 2008 only 2 children had rubella: one under 1 year of age and one over 7 years of age. In 2009 no cases of rubella were registered among children. On the whole, the share of children under the age of 14 in the age structure of patients ranged from 97.9% in 1987 to 89.7% in 1999. After immunization started, the share of children among patients with rubella decreased from 93.3 % in 2000 to 0 in 2009 (Figure 5).
Fig. 5. Age structure of patients with rubella in Arkhangelsk oblast in 1986 – 2009
To eliminate rubella in the population, it is necessary to cover no less than 95% of targeted groups by preventive vaccination. In Arkhangelsk oblast since 2005 timely vaccination has been provided for 95% or more of children 2 years of age. This high level of immunization has contributed to the reduction of rubella incidence in Arkhangelsk oblast.
The incidence of rubella depends not only on the number of vaccinated children under 2 years of age, but also on the number of people vaccinated against rubella in the population. The maximum number of people was vaccinated in 2001, in the next three years (2002-2004) the number of immunized people was lower. Starting from 2005, the number of people vaccinated against rubella began to increase (Figure 6). Specific preventive measures taken in 2007 helped to stop a further increase in rubella incidence.
Fig. 6. Rubella incidence dynamics and number of people vaccinated against rubella in Arkhangelsk oblast in 2000-2009
The analysis of long-term data shows a steady decline in the incidence of measles and rubella in Arkhangelsk oblast. In 2008-2009, the lowest incidence of rubella of less than 1 case per 100,000 population was reached. Since 2007 no cases of measles have been registered. The main preventive measure against the diseases is vaccination. The vaccination coverage level of the susceptible contingents allows indirect estimation of herd immunity and, in combination with the incidence dynamics, helps to assess the efficiency of specific prevention. The high level of coverage of children at the age of 2 years by vaccination against measles in Arkhangelsk oblast contributed to a considerable reduction of the disease incidence. However, disease elimination and eradication can be facilitated if children are vaccinated against measles twice. In 2003, when the vaccination coverage among children of 6 years reached 95.1% and booster vaccination against measles was underway, measles was eradicated in the region. Nevertheless, elimination does not imply complete absence of the disease incidence, since the infection can be easily imported into the region. The last registered cases of measles in Arkhangelsk oblast (a child in 2003 and an adult in 2006) were imported. That is why it is important to continue vaccination even after the elimination of infection.
In the pre-vaccinal period, rubella showed cyclic dynamics with periodic rises and with involvement of children in the epidemic process. Children of 3-6 and 7-14 years of age suffered most often from rubella. After the introduction of mass immunization for children, the age structure of patients changed: adults started to prevail. The share of people over 14 years of age increased by 15 times from 2000 to 2009 thus indicating the necessity of vaccinating adults.
It is possible to conclude that the Rubella Elimination Program was effective. After 9 years of mass immunization, the incidence in Arkhangelsk oblast was less than 1 case per 100,000 population. This accomplishment is the result of wide vaccination coverage and should be maintained at a high level.
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