The single-dose vaccination strategy has been highly effective for controlling HAV infection in all age groups till now in Argentina. Long-term surveillance will be critical to document the sustained success of this unique intervention.

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Single-dose universal hepatitis A immunization in 1-year-old children resulted in sustained immunologic protection for up to 9 years in Argentina. These findings, along with the low current disease burden, confirm the success of the intervention.

BackgroundSingle-dose Hepatitis A Virus (HAV) vaccination was implemented for all Argentinean children aged 12 months in 2005, instead of the standard two-dose schedule. Previous studies demonstrated a dramatic decline in HAV infection rates, fulminant hepatitis, and liver transplantation along with low viral circulation and high prevalence of protective antibody response 8 years following the intervention. This study assessed long-term seroprotection against HAV after vaccination with this novel scheme.MethodsChildren who received one dose of HAV vaccine at 1 year of age, at least nine years before enrollment, were included at three centers in Argentina between May 2015 and April 2016. Demographic and socio-economic characteristics of the child, mother and house were collected through a questionnaire after informed consent signature. Blood samples were tested for anti-HAV antibodies. Antibody titers ≥10 mIU/mL were considered seroprotective. Logistic regression analysis was done to evaluate associations between different variables and seroprotection.ResultsOf 1119 children included, 97.0% lived in urban areas, 92.7% had safe water access and 57.8% had sewers at home. Mean age was 10.7 years, and the mean post-vaccination interval was 9.7 years (Range: 9.0–11.3 years). Of the total, 87.6% had protective antibodies against HAV. Higher seroprotection rates were observed in Santa Fe compared with the global rate (91.9% vs. 87.6%; OR 1.94 (95% CI: 1.27–2.95); P = 0.002). In contrast, lowest rates resulted in San Justo, Buenos Aires (81.4% vs. 87.6% OR 0.45 (95% CI: 0.32–0.65); P <0.001). No association between socio-economic variables and seroprotection was found. Geometric mean concentration (GMC) of HAV Ab titers was 28.0 mIU/mL (95% CI: 26.8–29.3 mIU/mL).ConclusionSingle-dose universal hepatitis A immunization in infants resulted in sustained immunologic protection up to 11 years in Argentina. Lower seroprevalence rates in San Justo have no clear reason and were not associated with an increase in HAV cases in that area. These findings, along with the low current disease burden confirm the success of the intervention.Disclosures All authors: No reported disclosures.

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BackgroundIn the last years, there has been an increase in incidence of cases of measles in high and middle-income countries. In Argentina, measles elimination was achieved in 2000, with no circulation of measles virus since then; vaccination iscompulsory (two doses MMR vaccine) and coverage is reported to be roughly 85%. The aim of this study was to determine seroprevalence of antibodies to measles in adults, analyzed according to HIV status.MethodsCross-sectional study. All serologic tests requested for measles antibodies in patients aged >18 years between January 2015 and December 2017 in an Infectious Diseases Reference Center in Buenos Aires were retrieved and analyzed according to HIV status and age group. All determinations were done with VIDAS¨ Measles IgG, Biomeriex. Chi-squared and Fisher’s exact tests were used for comparisons.ResultsWe included 2,663 patients with determinations for measles performed in the mentioned period. Of those, 348 were HIV(+), with mean (±SD) age: 34.7(±6.2) years, 85% male (86% MSM), mean (±SD) nadir CD4 (cells/mm3): 369.6(±219.5); 89% VL< 50 copies/mL; and 2,315 were HIV(–), with mean age(±SD): 31(±5.9) years, 67% female. There was a high proportion of seronegative subjects to measles in both groups, but significantly higher in HIV+ patients (40.8% vs. 33.2%; P = 0.005). However, when analyzed by age group, in those <40 years the proportion of seronegativity to measles was higher (HIV+: 45.3% vs. 31.3%, P = 0.02; HIV-: 38.3% vs. 20.2%, P < 0.001; Figure 1). Patients older than 50 years (the most prone to having beenexposed to measles virus) had the highest prevalence of measles antibodies (>92% in both groups; Figure 2); and those younger than 40, the lowest (55% in HIV+ and 62% in HIV−). Stratification by gender did not change any of these findings. In HIV+ persons, seronegativity to measles was not associated with nadir of CD4 < 200 (P = NS). ConclusionWe found a very high proportion of subjects without protective antibodies to measles among those <40 years (higher in HIV+ patients). This is interesting since in Argentina the vast majority of people <40 should have been vaccinated atleast once. Lack of circulation of measles might accelerate waning of antibodies. There might be an increased risk of measles in young people, especially in HIV+ persons; measures to evaluate this situation and eventually (re)vaccinate susceptiblepersons is warranted.Disclosures E. Bissio, MSD: Employee, Salary. M. E. Perez Carrega, MSD: Employee, Salary. J. L. Montes, MSD: Employee, Salary.