Assessment of the manifestations of the measles epidemic process in Voronezh region for 1940-2023

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Relevance. Measles is the third infection after smallpox and polio, the successful eradication of which began with vaccination. Before the introduction of universal mass immunization in 1967, measles had a significant impact on overall mortality worldwide. This was facilitated by such features of the epidemic process as ubiquity, the rapid development of epidemics and the predominant defeat of the child population. Today, our country has a program whose goal is to completely eliminate the incidence of measles by 2025. However, the elimination target has not yet been achieved.

Currently, despite the availability of a safe and effective vaccine, the infection continues to pose a serious threat to the health and life of the population. There is a complication of the epidemiological situation regarding measles, both in the world and in the Russian Federation [1].

According to WHO, in 2022, more than 155.5 thousand cases of the disease were registered in 153 countries. In Russia, in 2021, 1 case of measles was registered, in 2022 - 102 cases, in 2023 - already thousands of cases in 44 regions, and the Russian Federation was among the three countries with the largest number of measles cases in the world. From January to May 2023, the incidence of measles in our country reached a record level (an increase of 300 times) and amounted to more than 8 thousand cases [2-4].

Target. To study the manifestations of the measles epidemic process in the Voronezh region for the period 1940 - the first half of 2023.

Objectives:

1. To analyze the long-term dynamics of measles incidence among the population of the Voronezh region.
2. To characterize measles foci.
3. To identify factors influencing the formation of measles foci.

Materials and methods of research. To solve the set tasks, an analysis of morbidity data was carried out according to Form 2 of Rosstat and 104 epidemiological investigation cards of a case of measles or suspected of this infection for 2011-2023. on the territory of the Voronezh region. The materials were assessed both by general categories - gender, age, address, place of work, and by questions of vaccination history, presence of contact persons and the connection of the disease with migration. The process of formation of foci was considered according to the following criteria: without the spread of infection and with further spread of infection both in the foci and the spread of infection beyond its boundaries. Outbreaks were assessed by the number of infected individuals, the duration of the existence of the epidemic focus in time and the presence of repeated cases of measles.

Statistical analysis of the data was carried out using the Microsoft-Excel 2010 software product with the calculation of average (M) and relative values, standard error (m), reliability was determined differences by Student's t-test and χ2 (chi-square). Differences were considered statistically significant at a significance level of p<0.05.

The age of the patients ranged from 0 to 49 years (average age 18.30 ± 1.48 years), of which 56 children (average age 6.34 ± 0.71 years) and 48 adults (average age 32.25 ± 1.41 years).

Having assessed the epidemiological investigation cards, it was found that the diagnosis of “measles” was made equally to children and adults, with a slight advantage in favor of the child population (53.85% and 46.15%). It is noted that the incidence was more common among men (60.58%), without distribution into age groups.

The diagnosis of measles in the vast majority of cases (85.58%) was established on the basis of clinical and laboratory data. Laboratory testing of patients was carried out at the optimal time for collecting biological material in 76.4% of cases.

Research results. Since 1940, the incidence of measles in the Voronezh region has been characterized by pronounced cyclicality. The indicators were at a fairly high level and in some years exceeded 1000 per 100 thousand population (1956 - 1006 cases and 1963 - 1039 cases per 100 thousand population). After the introduction of mass immunization, the incidence of measles infection had a steady downward trend, but remained cyclical (1967 - 601.3 cases, 1970 - 50.5 cases, 1980 - 109.3 cases, 1990 - 14.2 cases per 100 thousand population). From 1990 until 2011 cases of measles were more sporadic. Having analyzed the results obtained, over a thirteen-year period (2011 – the first half of 2023) an uneven distribution of measles incidence was observed in the Voronezh region. Since 2011, undulating rises have been observed with the highest level in 2012 - 1.33 cases per 100 thousand population (CI 0.86-1.80); in 2014 – 1.29 cases per 100 thousand population (CI 0.82-1.76); in 2019 - 0.69 cases per 100 thousand population (CI 0.35-1.03) and in 2023 - 0.69 cases per 100 thousand population (CI 0.08-0.54). The highest average annual growth rate was recorded in 2014 (658.82%), 2018 (425.00%), 2012 (395.59%) and 2019 (228.57%), while the highest rate of decline was in 2020 (-100 .00%), 2015 (-89.92%), 2013 (-87.22%), 2016 (69.23%). Over a thirteen-year period, the incidence of infection increased from 0.27 cases (CI 0.06-0.48) to 0.31 cases (CI 0.08-0.54) per 100 thousand population. The growth rate was 115%, and according to the average annual growth rate, there is a pronounced tendency towards an increase in incidence (the average annual growth rate was 150.96%).

During periods of upswing (2012, 2014 and 2019) and downturns, measles incidence rates differed markedly. Children were considered at risk (4.01 cases (CI 1.83-6.19) versus 0.90 cases (CI 0.48-1.31) per 100 thousand adults; 5.47 cases (CI 2.94 -8.00), versus 0.61 cases (CI 0.27-0.96) per 100 thousand population and 3.18 cases (CI 1.45-4.91) per 100 thousand population versus 0.16 cases (CI -0.02-0.33) per 100 thousand population). In addition, in 2012 and 2014. significant differences were noted among the indicators of men and women: men were sick significantly more often (2.86 cases (CI 1.54-4.19) versus 0.76 cases (CI 0.35-1.18) per 100 thousand female population and 2.92 cases (CI 1.53-4.31) versus 0.76 cases per 100 thousand population (CI 0.35-1.18), respectively). In other years, significant differences in age and sex groups were not established.

When assessing the prevalence of measles infection, 61 foci of measles infection were registered with a total number of cases of 104. Thus, in 2011, 2 foci of measles were identified, in 2012 - 19 foci, in 2013 - 3 outbreaks, in 2014 – 12 outbreaks; in 2015 – 2; in 2016 and 2017 – 1 outbreak in each; in 2018 – 5 outbreaks; in 2019 - 10 outbreaks, in 2023 - 6 outbreaks. In the period from 2020 to 2022, the incidence of measles in the Voronezh region was not registered.

Over 13 years, 41 outbreaks were recorded with one case of the disease. The largest number of single outbreaks was identified in 2012 (11 outbreaks). There are 8 outbreaks with two confirmed cases of measles. The largest number of such outbreaks was identified in 2012 (5 outbreaks). With three cases of infection, 4 foci were identified with a predominant number also in 2012 (2 foci). There are 4 outbreaks with four cases of measles. The largest number of them was identified in 2014. It was found that during the same period, outbreaks with five and seven cases were recorded, 2 and 1, respectively.

During the study period, 11 outbreaks with 3 or more cases of the disease were registered (2011 - 1 outbreak with 5 cases; 2012 - 3 outbreaks with a total number of cases 10; 2014 - 5 outbreaks with a total number of cases 23; 2019 - 2 outbreaks with a total number of 7 cases).

The largest contribution to the structure of measles incidence was made by local cases - 74 (71.15%), in relation to imported ones - 30 (28.85%), p<0.001. Among the sick population, people who did not travel outside the Voronezh region and did not have measles vaccinations predominated. The spread of infection occurred through organized groups (universities, medical organizations and places of work of citizens).

Of the 61 outbreaks, 19 were registered with imported cases. Of these, 15 outbreaks had one isolated imported case, but there were also outbreaks where the imported case caused further spread of the infection. 4 such foci were identified. Measles was mainly imported from the Republic of Dagestan, the Chechen Republic, St. Petersburg, Moscow, Tambov, Stavropol Territory, Volgograd, Rostov and Lipetsk regions. Imported cases for the period from 2011 to 2015 were significantly more common than for the period from 2016 to 2019, 2023 (p = 0.01).

The share of family cases in the structure of measles incidence was 46.15%. Measles outbreaks with further spread within the family were identified in 2012, 2014, 2015, 2019, 2023.The total number of family outbreaks is 16, of which 11 outbreaks with a total number of cases of 31 were isolated and did not spread beyond the same family. The other 5 foci are interconnected and have a common primary focus, which caused further spread of the infection.

Analysis of the vaccination history showed that the largest proportion of measles cases were among persons with unknown status (45.19%) and unvaccinated (39.42%). In the structure of those who were immunized (15.38%), measles was recorded in 81.25% of those who were revaccinated and 18.75% of those who were not revaccinated.

Discussion. Currently, immunoprophylaxis is of great importance in controlling the epidemic process associated with vaccine-preventable infections. Despite the availability of an actively used vaccine and the constant desire of state sanitary and epidemiological surveillance authorities to vaccinate various categories of citizens, measles does not lose its significance due to possible imported cases and refusal to vaccinate. A large non-immune stratum among the population that emerged during the measles-free epidemic situation of the early 21st century, extensive anti-vaccination propaganda on the Internet, and a low level of trust in medical workers could have contributed to the increase in morbidity and the emergence of outbreaks [5]. The importation of measles from the countries of the former Soviet Union is due to problems with vaccination in these territories [6]. Having assessed the long-term dynamics of measles incidence, we can conclude that it tends to cyclical rises, mainly associated with population migration to other countries, cities and regions and refusal of vaccination. Over the past 13 years, there has been an increase in incidence, due to the highest growth rates in years of rising incidence. The largest outbreaks of measles in the Voronezh region were registered in 2012 (19 outbreaks), 2014 (12 outbreaks) and 2019 (10 outbreaks).

During the study, it was found that persons with an unknown vaccination history made a large contribution to the structure of measles incidence (45.19%) and unvaccinated (39.42%). Morbidity among vaccinated people may be associated both with imperfect immunity in the sick and with “artificially documented” vaccination created in an effort to fulfill the vaccination plan by medical workers [3]. 

Monitoring the circulation of the pathogen, high awareness of citizens and the interest of medical workers in immunization against infectious diseases play an important role in vaccination prevention of the population and the formation of collective immunity.

Conclusions:

1. The incidence of measles in the Voronezh region is not uniform. For 2011-2023 the incidence of infection increased from 0.27 cases (CI 0.06-0.48) to 0.31 cases (CI 0.08-0.54) per 100 thousand population. The average annual growth rate was 150.96%, which indicates a pronounced trend towards an increase in incidence.
2. When analyzing the prevalence of the disease over a thirteen-year period, 61 outbreaks of measles were identified with a predominance of outbreaks with single cases (50 outbreaks).
3. Local cases of measles for the period 2011-2023. prevailed (71.15%) over imported ones (28.85%). The infection was imported from various regions of the Russian Federation, the Republic of Dagestan and the Chechen Republic.
4. The largest number of cases were among persons with unknown vaccination status (45.19%) and unvaccinated (39.42%). The presence of people vaccinated against measles in the structure of the disease requires further study.

About the authors

Maria Alexandrovna Pobezhimova

Voronezh State Medical University named after. N. N. Burdenko

Email: pobezhimova.2000@mail.ru
ORCID iD: 0000-0001-9112-7100
SPIN-code: 4940-3167
Russian Federation, 10 Studencheskava Street, 394036 Voronezh, Russian Federation

Nataliya Vadimovna Gabbasova

Voronezh State Medical University named after. N. N. Burdenko

Email: natalia_gabb@mail.ru
ORCID iD: 0000-0001-5042-3739
SPIN-code: 6629-4401

Doctor of Medical Sciences, Professor of the Department of Epidemiology

Russian Federation, 10 Studencheskava Street, 394036 Voronezh, Russian Federation

Liliya Alexandrovna Yatsenko

Voronezh State Medical University named after. N. N. Burdenko

Author for correspondence.
Email: yatsenko.lili@yandex.ru
ORCID iD: 0000-0001-6095-4760
SPIN-code: 2075-3944

Candidate of Medical Sciences, Associate Professor of the Department of Epidemiology

Russian Federation, 10 Studencheskava Street, 394036 Voronezh, Russian Federation

References

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