To the Editor—We read with great interest the article by Patel and colleagues [1] on the changes in measles epidemiology and how strengthening of immunization programs and closing immunity gaps are important to reach the goal of measles elimination. Italy has never achieved the measles elimination goal although considerable resources have been deployed for at least 3 decades to increase vaccination coverage [2]. As a result, local outbreaks occur almost every year, even in areas where measles vaccination coverage at 24 months of age is near or above 95% [2], and fatalities are not uncommon, as in 2018 when 8 measles deaths were reported [3]. In January 2020, alarmed local media reported that 40 measles cases had occurred in the past month in Apulia, a large region in southern Italy, and that most cases were adults between 23 and 50 years of age [4]. The news was indeed alarming as, since 2015, the maximum number of reported measles cases per year in Apulia was 58 in 2019 [3].
To better understand the level of susceptibility to measles in Apulia we performed a serological study in the province of Bari, the regional capital city. Serum samples were collected as residual sera at local laboratories between 2015 and 2018, anonymized, and stored at our sera bank in compliance with the Italian ethics law. Samples were stratified by sex and age groups (3–10, 11–18, 19–30, 31–40, 41–50, and > 50 years). Anti-measles virus immunoglobulin G (MeV IgG) was measured by Enzygnost AntiMeasles Virus/IgG (Siemens) enzyme-linked immunosorbent assay (ELISA) commercial kit. According to the manufacturer’s instructions, samples with MeV IgG value <150 mIU/mL were considered negative, and for the purpose of this study indicated susceptibility to measles.
Out of 486 samples, 87.2% (95% confidence interval [CI], 83.9%–90.1%) were positive for MeV IgG and 12.8% (95% CI, 9.9%–16.0%) were negative. Significant differences were found in susceptibility to measles by age groups (P = .003), with particularly high proportions of susceptibles up to the age of 18 years (11–18 years old, 22.2%; 95% CI, 14.5%–31.7%), an age group that should have received measles vaccination. Notably, 17.2% (95% CI, 10.3%–26.1%) of subjects aged 19–30 years were found to be susceptible to measles, in accordance with the median age reported for measles cases in Italy [3] and already highlighted for pregnant women in the same province [5]. A similar trend between the level of MeV IgG titers and the proportion of susceptible subjects was observed for all age groups with IgG titer differences found to be statistically significant (P < .0001) (Figure 1). No significant differences were found by sex (data not shown).
Prevalence and geometric mean titers (GMTs) of anti-measles virus immunoglobulin G (MeV IgG) by age group. Prevalences of positive (grey bar) and negative (striped bar) samples are shown. Horizontal lines indicate MeV IgG GMTs with 95% confidence intervals.
The high level of susceptibility to measles that we found in our samples helps us to understand the measles outbreak in Apulia that started in January 2020. In Apulia, measles vaccination coverage at 24 months increased from 84.15% in 2015 to 94.18% in 2018 [6]. However, measles transmission can be interrupted only by achieving high population immunity in all age groups. Of the 4 children involved in the recent cases in Apulia, 2 were too young to be vaccinated and contracted the infection from parents who were not immune, while the other 2 were not vaccinated because of parents’ convictions [4]. In Italy, obstacles to reach and maintain high measles vaccine coverage (>95%) are vaccine hesitancy and antivaccination positions held by both parents [7] and health professionals [8]. Some Italian politicians elected in parliament and in the government have built their consensus by openly supporting “noVax” movements that preferentially target measles vaccination [9, 10]. A strong and durable engagement by all public health professionals in Apulia and in all Italy is needed to increase and maintain awareness of the importance of measles vaccination.
Notes
Potential conflicts of interest. All authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
