In our study, measles seroprevalence was 46.1%, and the seroprevalence was higher in the group born between 1986 and 1997 than in the group born between 1998 and 2004. It was also determined that the seropositivity rate exceeded 50% in those born before 1997.
There are different data in the literature regarding measles seroprevalence in Turkey. In a study examining measles serology in students residing in our university dormitory, measles seropositivity was found to be 100% in the population born before 1986 [15]. In the study conducted by Açıkgöz et al., it was found that measles seropositivity was higher among students aged 21 and older and those with lower income levels in Turkey [16]. In a study conducted by Köse et al., the seropositivity rate was found to be 72% in the group aged 18–25, 88.8% in the group aged 26–35, and 95.2% in the group aged 36–45 [17]. These findings are similar to the finding of lower seropositivity rate in the younger group in our study. In a study that included employees of a university hospital and medical students, measles seroprevalence was found to be 57% [18]. In the same study, susceptibility rate was 46% in the group aged 18–25, while it was determined that the entire group over the age of 38 was immune [18]. Consistent with previous studies, our findings indicate that younger individuals demonstrate increased susceptibility to measles.
Medical students, as early-career healthcare workers, are at particularly high risk of exposure to measles due to their frequent patient contact in clinical settings. The lower seroprevalence observed in younger individuals, particularly those born between 1998 and 2004, suggests that a significant proportion of medical trainees may be susceptible to measles infection. Given that medical students will transition into clinical settings, ensuring their immunity is important for both personal safety and infection control in healthcare settings.
In different studies reported from Europe, it has been observed that the seropositivity rate is lower among younger healthcare workers, similar to the results in our country [19, 20]. In a study reported from Latvia in 2022, a seroprevalence of 77.3% was found in healthcare workers, while the lowest seroprevalence was in the 26–35 age group at 53% [21]. The same study revealed that seronegativity for measles was higher compared to diphtheria among healthcare workers [21]. In a study reported from Korea, it was shown that while the general measles seropositivity in healthcare workers was 73%, immunity decreased to 42% in the group born after 1995 [22].
In our study, a strong negative correlation (r = -0.964) was found between year of birth and measles seroprevalence, indicating that younger individuals have lower immunity to measles compared to older groups. This finding is particularly important when considering the seroprevalence patterns across age groups. Individuals born between 1998 and 2004 exhibited lower measles seroprevalence, suggesting higher susceptibility in this group. Several factors may contribute to this observed decline in immunity. First, waning vaccine-induced immunity over time may be a possible explanation. Unlike natural infection, which usually provides lifelong immunity, vaccine-induced immunity is known to wane over time, particularly in the absence of booster doses or exposure to circulating wild-type virus. In addition, gaps in vaccination coverage or primary vaccine failure in this group may have led to a lower seroprevalence rate. In contrast, higher measles seropositivity was found in older individuals born between 1986 and 1997. This group may have been more frequently exposed to wild-type measles virus, which confers immunity from natural infection, which is known to be more stable and durable than vaccine-induced immunity. Before widespread implementation of measles elimination programs, periodic outbreaks may have contributed to the strengthening of herd immunity, allowing individuals to acquire strong and durable immune responses.
It is thought that the low measles seroprevalence in the group born between 1998 and 2004 may be related to the vaccination policies in our country. An examination of the historical vaccination policies in our country reveals that 1998 marked the year when second dose of the monovalent measles vaccine was first administered to school-age children, and the monovalent measles vaccine continued to be used until 2006. It is expected that 93–95% protection will be achieved after a single dose of monovalent measles vaccine, and 97–99% after a second dose. This suggests that the low seroprevalence rate found in our study may be due to disruptions in the implementation of new vaccination practices. Since the vaccination histories of the participants could not be obtained, no definitive comment could be made on this matter. Secondary vaccine failure and waning measles immunity are also known to play a role in low seroprevalence [23]. Adolescents and young adults, whose immune systems may weaken over time, are particularly affected by these factors. These groups may be more vulnerable to disease in later years, as immunity levels may decline after vaccination. Additionally, individuals with diseases or medical conditions that suppress the immune system may have waning immunity over time, which may increase susceptibility to measles infection.
In our study, no relationship was found between measles seropositivity and gender. In another study conducted in 2012 on healthcare workers, it was shown that the immune response did not change significantly by gender, while a study conducted in 2015 found that seronegativity was higher in females [24, 25]. More recent studies including the young adult group showed no difference between genders, similar to our study [17, 26].
Looking at the studies reporting measles seroprevalence from Turkey, regional differences can be seen. In Şanlıurfa, it was reported that measles seroprevalence was 52.6% in the 18–21 age range and 77.7% in the 22–25 age range in 2023. In a study conducted in Manisa in 2017, seroprevalence was found to be 74.1% in the 18–29 age group [27]. There is no comprehensive study in the literature that provides seroprevalence according to regions. In our study, measles seroprevalence was found to be the lowest in the Eastern Marmara Region (34.5%) and the highest in the Western Black Sea Region (59.5%). The Eastern Marmara statistical region includes Kocaeli, Sakarya, Düzce, Bolu, and Yalova. Although measles seroprevalence was expected to be relatively high in the Eastern Marmara Region due to its socioeconomic status, the lowest seroprevalence was observed in this region in our study. After the 17 August 1999 Gölcük Kocaeli and 12 November 1999 Düzce Earthquakes, there were significant disruptions in the supply of vaccines and the implementation of healthcare services in the region. It is thought that these painful historical events may be a reason for the current low seroprevalence in the young adult population born and raised in the region.
Our study has several limitations. It was conducted at a single center, and therefore it is not possible to make a definitive conclusions about measles seroprevalence in healthcare workers and the general population on a national or international level. Vaccination records of all participants could not be obtained, and since some of the participants who were asked about their vaccination history were unable to recall their vaccination status, preventing a thorough assessment. Additionally, since the participants who applied to our polyclinic voluntarily were included in the study, differences were observed in the number of applications over the years.
Our study covers a 14-year period and evaluates a single group within healthcare workers. To the best of our knowledge, this is the first study in our country to compare measles seroprevalence with birth year and place of birth among healthcare workers.