Measles antibodies in cord blood in Portugal: Possible consequences for the recommended age of vaccination

Population measles seroprevalence: Heterogeneity by birth-year cohort

Objective

This work sought to estimate population measles seroprevalence and heterogeneity in the antibody concentration distribution that could be explained by the birth-year cohort according to the opportunity of viral and vaccine exposure, applied to data from Medellín, Colombia.

Methods

Prevalence of IgG antibodies was analyzed for measles based on a population study with a random sample of 2098 individuals from 6 to 64 years of age. Finite mixture models were used to estimate global seroprevalence and that of three birth-year cohorts (I: born up to 1982; II: 1983-1994; III: born since 1995). Multiple linear regression permitted adjusting the concentration of antibodies by cohort, zone, and sex.

Results

Globally, seronegativity was 6.5% (95% CI 4.9- 8.6), seropositivity of 78.4% (95% CI 75.1-81.4), and equivocal of 15.1% (95% CI 12.5-18.1). Two components were found with skewed normal distribution, which reclassified those equivocal as seropositive. Differences were observed by cohort in the geometric mean of antibodies [Cohort I: 1704.6; II: 562.2; III: 802.1 milli-international units per milliliter (mIU/mL] and seronegativity (Cohort I: 4%; II:13.3%; III: 8.9%). Antibody concentration increased by 1.26 mIU/mL in residents in the rural area, while diminishing in individuals from cohort II (by 3.02 mIU/mL) and cohort III (by 2.14 mIU/mL).

Conclusion

The younger cohorts (II and III) had a lower antibody concentration (higher seronegativity), indicating the need to monitor periodically seroprevalence and an eventual reestablishment of the transmission in these groups with higher risk of infection.

Seroprevalence of Measles in Pairs of Mothers and Newborns in Southern Greece

Maternal immunoglobulin G (IgG) antibodies that are passively transferred to newborns through the placenta confer protection if they are exposed to measles virus. A measles outbreak occurred in several European countries including Greece, between 2016 and 2018. A prospective study was conducted in the General Hospital of Lakonia, regarding the measles seropositivity status of mother and newborn pairs. IgG antibody titer for measles was measured in serum samples acquired from pairs of mothers and newborns. The samples were analyzed through quantitative enzyme-linked immunosorbent assay, and antimeasles IgG >200 IU/mL was considered to be protective. Demographic data for mothers and neonates and data regarding immunization status of mothers were analyzed. Study population included 206 mothers and their newborns. In total, 12.6% of mothers (n = 26) and 10.7% of newborns (n = 22) did not have protective serology. A statistically significant positive linear association between maternal and neonatal antibodies was found (rho = 0.924) (p = 0.001). Neonates whose mothers were seropositive had higher antibodies [geometric mean concentration (GMC): 804.8 (728.3-889.2)] than neonates whose mothers were seronegative/borderline [GMC: 97.7 (64.2-148.8)] (p = 0.001). In the study area, a significant rate of mothers and newborns was found to have nonprotective measles serology that exceeds the limit required for herd immunity. Vaccination coverage in women of reproductive age should be increased to reduce potential for future measles epidemics.

Measles Serostatus in Mothers and Their Newborns in Antioquia, Colombia: Implications for Measles Elimination

To describe the serostatus of measles IgG antibodies in pregnant women and newborns, placental transfer, and factors that determine being below the threshold of 150 mIU/mL, a cross-sectional study was conducted. Blood samples of 790 pregnant women at the time of delivery and 734 umbilical cord samples were analyzed from eight hospitals in the Aburrá Valley of Antioquia, Colombia. Measles IgG antibody measurement was performed with ELISA. The proportion of individuals with antibodies < 150 mIU/mL was 13.9% (95% CI: 12.2-15.8) in pregnant women and 11.1% (95% CI: 9.2-13.4) in newborns. The geometric mean of the antibody level of the pregnant women was 552 mIU/mL (95% CI: 504-605) and in the umbilical cord 662 mIU/mL (95% CI: 604-727). A positive correlation between pregnant woman and umbilical cord antibodies was found. The median ratio of measles IgG antibodies in umbilical cord/pregnant woman was 1.22 for all participants. A seroprevalence below the threshold of 150 mIU/mL was found in newborns whose mothers were born between 1983 and 1994, compared with those born before that period, when exposure to the wildtype virus was common (adjusted prevalence ratio: 3.6, 95% CI: 1.3-9.6). These findings suggest that there are gaps in measles immunity among women of childbearing age, before pregnancy. To close this immune gap and support efforts to maintain measles control, serological screening for measles antibodies should be routinely included in reproductive health and antenatal care programs to identify women without immunity who should be vaccinated before pregnancy or after delivery.

Vertically Transferred Immunity in Neonates: Mothers, Mechanisms and Mediators

Over the last years, an increasing number of outbreaks of vaccine-preventable infectious diseases has been reported. Besides elderly and immunocompromised individuals, newborns and small infants are most susceptible to infections, as their immune system is still immature. This vulnerability during infancy can be mitigated by the transplacental transfer of pathogen-specific antibodies and other mediators of immunity from mother to the fetus during pregnancy, followed postnatally by breast milk-derived immunity. Since this largely antibody-mediated passive immunity can prevent the newborn from infections, neonatal immunity depends strongly on the maternal concentration of respective specific antibodies during pregnancy. If titers are low or wane rapidly after birth, the protection transferred to the child may not be sufficient to prevent disease. Moreover, emerging concepts propose that mothers may transfer active immunity to the newborns via vertical transfer of pathogen-specific T cells. Overall, a promising strategy to augment and prolong neonatal immunity is to vaccinate the mother before or during pregnancy in order to boost maternal antibody concentrations or availability of specific T cells. Hence, a large number of pre-and postconceptional vaccine trials have been carried out to test and confirm this concept. We here highlight novel insights arising from recent research endeavors on the influence of prenatal maternal vaccination against pathogens that can pose a threat for newborns, such as measles, pertussis, rubella and influenza A. We delineate pathways involved in the transfer of specific maternal antibodies. We also discuss the consequences for children's health and long-term immunity resulting from an adjustment of prenatal vaccination regimes.

Measles Antibody Levels in Young Infants

BACKGROUND

Infants are often assumed to be immune to measles through maternal antibodies transferred during pregnancy and, in many countries, receive their first measles-containing vaccine at 12 to 15 months. Immunity may wane before this time in measles-eliminated settings, placing infants at risk for measles and complications. We investigated humoral immunity to measles in infants <12 months of age in Ontario, Canada.

METHODS

We selected sera collected at a tertiary pediatric hospital from infants <12 months who were born at ≥37 weeks' gestational age. We excluded infants with conditions that affect antibody levels. We selected ≤25 sera from 8 predetermined age bands and tested them for measles-neutralizing antibody using the plaque-reduction neutralization test. We calculated the proportion immune at each age band, and predictors of infant susceptibility were assessed by using multivariable logistic regression and Poisson regression.

RESULTS

Of 196 infant sera, 56% (110 of 196) were from boys, and 35% (69 of 196) were from infants with underlying medical conditions. In the first month, 20% (5 of 25) of infants had antibodies below the protective threshold, which increased to 92% (22 of 24) by 3 months. By 6 months, all infants had titers below the protective threshold. In a multivariable analysis, infant age was the strongest predictor of susceptibility (odds ratio = 2.13 for each additional month increase; 95% confidence interval: 1.52-2.97).

CONCLUSIONS

Most infants were susceptible to measles by 3 months of age in this elimination setting. Our findings inform important policy discussions relating to the timing of the first dose of measles-containing vaccine and infant postexposure prophylaxis recommendations.

Mumps antibodies in the cord blood: Association with maternal recall of mumps. Possible consequences for vaccination strategies

The present study aims to contribute to the evaluation of the serological impact of vaccination against mumps in Portugal, measuring anti-mumps IgG (MuIgG) levels in cord sera and the corresponding proportions of seropositive newborns, and their association with potential predictive variables. The data from this study came from 198 umbilical cord sera. Detailed vaccination records were available for all mothers. MuIgG were measured in the sera, using a commercial immunoassay. The geometric mean concentration (GMC) of MuIgG was 31.7 RU/ml. Seropositive/immune sera (concentration ≥16 RU/ml) were 75.3%. While 49 mothers were "unsure" about ever having had mumps, 46 said they had had the disease and 103 said they had not had it. Eighty eight women did not receive a single dose of MMR while the other received 1 or 2 doses, with different combinations of vaccine strains. This study found that recalling mumps was predictive of higher MuIgG GMC and seropositivity. Maternal age and vaccination status were not associated with GMC or seropositivity. Nevertheless, in the small subset of newborns from vaccinated mothers not recalling mumps, receiving two doses was predictive of higher GMC than just receiving one. Maternal recall of mumps is highly predictive of seropositivity while not recalling the disease results in numerous false-negatives. This is consistent with other studies and with the fact that infection with mumps virus can result in a wide range of clinical manifestations. We agree on the need for further research to support a recommendation of a three (or more)-dose MMR strategy but we also believe that evidence is fast accumulating in favour of a higher dose strategy. The issue of waning immunity due to vaccines when vaccination succeeds in controlling (and nationally eliminating) target diseases like measles and mumps must be urgently taken into account.

Rubella antibodies in cord blood sera in Portugal: association with maternal age and vaccination status

This study evaluated the impact of maternal vaccination against rubella on the levels of specific rubella IgG (rIgG) in 198 newborn cord sera samples. Detailed maternal vaccination data were available. Specific rIgG was measured using a commercial enzyme immunoassay. Most mothers (78.8%) had been vaccinated against rubella at least once in their lives. In 15 (7.6%) cord sera samples, the concentration of specific rIgG was below 11 IU/ml, which was classified as seronegative. Statistical analysis using multiple logistic regression (n = 198) showed that newborns of mothers born between 1986 and 1995, and those born to unvaccinated mothers, were more likely to be seronegative (odds ratio (ORs) 5.2 and 4.9, respectively, adjusted for sex and gestational age). For vaccinated mothers (n = 156), those born between 1986 and 1995 were more likely to have seronegative newborns (OR 11.5 adjusting for sex, gestational age and time since last vaccination). Mothers of the 15 (7.6%) seronegative newborns might have been susceptible to rubella during pregnancy. Checking the vaccination status therefore recommended.

Waning of measles maternal antibody in infants in measles elimination settings - A systematic literature review

INTRODUCTION

Most infants are born with immunity to measles through maternal antibodies transferred in pregnancy, which decay over time. However, in measles elimination settings, where measles does not circulate endemically and most immunity is from immunization rather than infection, maternal antibody levels are lower. This results in infant immunity that wanes earlier, and a wider susceptibility gap between maternal antibody decay and infant immunization than in non-eliminated settings. We aimed to systematically quantify the extent and duration of protection from measles in infants in settings that have sustained measles elimination.

METHODS

We conducted a systematic review of studies of measles maternal antibody waning in infants in measles elimination settings. We searched MEDLINE, Embase, CINAHL, Scopus, BIOSIS Previews, and Global Health databases for relevant studies. Studies were included if they were set in countries that had eliminated measles for ≥3 years, and if the study cohort included healthy, full-term, unvaccinated infants ≤12 months, born to healthy mothers, and reported a relevant measure of measles maternal antibody in infants. We assessed study quality using the MetaQAT tool.

RESULTS

We identified 4692 unique citations, eight of which met inclusion criteria. One study reported anti-measles antibody in cord blood, six reported antibody in infant sera, and one reported both. Two studies reported that 80 and 100% of infants were protected from measles at birth. One study reported no protection amongst 3-7 month old infants, and another reported limited protection in infants >4 months. The remaining studies reported the proportion of infants with detected antibody, but not the proportion immune.

CONCLUSION

Although limited, these data suggest that in settings that have sustained measles elimination, some infants are susceptible to measles well before the age of routine measles immunization. Setting-specific seroprevalence and vaccine effectiveness studies are required to evaluate this in different jurisdictions.