A Serosurvey to Identify the Window of Vulnerability to Wild-Type Measles Among Infants in Rural Mali

Abstract

As infants lose maternally derived antibody, they experience a period when antibody levels are insufficient to protect against measles yet may interfere with immunization. In Kangaba Mali, sera were collected from 89 2-8-month-old infants and 32 9-10-month-old infants without a history of measles or vaccination; post-vaccination sera were collected from 24 of the 9-10-month-old infants 3-5 weeks after receiving measles vaccine. Measles antibody was measured by plaque reduction neutralization (PRN) and enzyme linked immunosorbent assay. At two months of age, 30% had protective PRN titers; among six-month-old infants, none had protective titers. Prior to vaccination, 16% of 9-10-month-old infants exhibited protective titers; all demonstrated protective titers post-vaccination. The early onset of the window of vulnerability in Kangaba infants likely reflects the changing ecology of measles in Africa. Ways to protect these vulnerable infants against measles must be devised.

A Clinical Study to Assess the Safety and Immunogenicity of Attenuated Measles Vaccine Administered Intranasally to Healthy Adults

“…Subjects provided blood for antibody measurements prior to immunization and on days 14, 28 and 90. PRN titers were measured as previously described, 11 using an adaptation of the method described by Albrecht et al 12 Samples were tested in parallel with the 2 nd WHO International Measles Reference Serum (66/202). Seroconversion was defined as a 4-fold rise in antibody titers after vaccination.…”

Measles-specific Neutralizing Antibodies in Rural Mozambique: Seroprevalence and Presence in Breast Milk

“…This phenomenon may be accentuated in babies born of vaccinated mothers who potentially have lower titers of measles antibodies than do mothers who had natural infections. A decrease in vaccine-induced antibody titers with age has been well documented, 7,8,25,29,30 and is likely to affect transfer of maternal antibody. Moreover, human immunodeficiency virus (HIV) status of the mothers has been shown to affect transplacental transfer of measles antibodies.…”

“…Since 1997, the hospital and CISM have jointly operated a round-the-clock surveillance of all pediatric visits at the outpatient department and admission to the wards. The national EPI in Mozambique includes bacillus Calmette-Guérin (BCG) vaccination (at birth), polio vaccine (at birth, 8, 12, and 18 weeks of age), diphtheria-tetanus-whole cell pertussis-hepatitis B vaccine (8,12, and 16 weeks of age), and measles vaccine (9 months of age). The global measles vaccine coverage rate in the country has been increasing substantially, reaching approximately 90% in 1999, 27 including Manhiça District with 94.4% of coverage reported in 2001.…”

“…PRN titers were measured as previously described. 8,15 Briefly, plasma samples in serial dilutions were incubated with 100 plaque-forming units of wild-type measles virus Edmonston strain for 1 hour at 37°C in an atmosphere of 5% CO 2 and plated onto confluent Vero cells (no. CCL-81; American Type Culture Collection, Manassas, VA) in 12-well plates.…”

“…[4][5][6] In African countries, a sizable proportion of measles cases occur among young infants during the window of vulnerability when placentally transferred antibody diminishes below protective levels (at approximately 4-8 months of age), but the infant has not yet received measles vaccine. 7,8 There is growing evidence that measles vaccine-induced antibody levels wane over time, raising a concern that such a decrease in antibody levels could affect maternal passive immunity when vaccinated women reach childbearing years. 9,10 Thus, the window of vulnerability of an infant may be even greater in vaccinated women than in with women with natural measles infection.…”