In a recently published study Journal of Infectious Diseasesresearchers compared two methods of half-life estimation to estimate the half-life of maternal antibodies in infants against pertussis caused by the tetanus, diphtheria, acellular pertussis (Tdap) vaccine given to mothers during pregnancy.
Study: Evaluation of the half-life of pertussis-specific maternal antibodies after vaccination against tetanus, diphtheria, acellular pertussis during pregnancy (in premature infants). Image credit: RossHelen/Shutterstock.com
Background
Whooping cough or whooping cough is a bacterial disease of the respiratory system Bordetella pertussis. The infection is highly contagious, and the World Health Organization (WHO) estimates that as of 2018, there have been more than 150,000 cases of pertussis worldwide.
However, these estimates have been underestimated, and research suggests that the true burden of pertussis in infants is closer to five million, with about 86,000 deaths among infants under one year of age.
In many countries, the Tdap vaccine is included as an immunization option for mothers during pregnancy to increase placental transfer of maternal antibodies. B. whooping cough from mother to fetus, to improve the baby’s immunity against pertussis in the first weeks of life.
However, the production of antibodies in the infant may be affected by maternal antibodies present in the infant, necessitating an understanding of the half-life of maternal antibodies specific for pertussis.
The vaccination regimen for an infant can be decided based on how long maternal antibodies persist in the infant’s immune system.
About studying
In this study, researchers used data from two prospective cohorts to compare two approaches to half-life estimation and to identify covariates that significantly affect antibody half-life estimation. Potential dilution effects were also adjusted for by using infant weight gain as a surrogate measure for blood volume.
Two prospective cohort studies from Belgium and Thailand examined the half-life of maternal pertussis antibodies in infants.
In addition, both studies included pregnant women who received the Tdap vaccine between six and eight months of pregnancy, while the Belgian cohort included term and full-term infants, and the Thai cohort included only infants born after eight months.
A Thai study measured immunoglobulin G (IgG) antibody titers against pertactin, filamentous hemagglutinin and pertussis toxin using commercial enzyme-linked immunosorbent assay (ELISA) kits with a lower limit of detection (LLOD) of less than five IU/ml. international units per milliliter). A Belgian study used a home-developed electrochemiluminescent method with an LLOD of 2 EU/mL (Elisa units per milliliter) to measure antibody titers against the same three antigens.
Infant measurements were included in the analysis only if antibody titer measurements were available from birth (cord blood). At least one measurement above the specified LLOD was available prior to primary vaccination, and if measurements showed decay, antibody titers prior to primary vaccination were lower than antibody titers in intestinal blood.
Two approaches – direct and indirect – were used to estimate the half-life of antibodies against each of the three antigens. The direct method assumed a constant decay rate, while the indirect method used a linear mixed-effects model to estimate the decay rate.
Results
The results showed that both half-life estimation methods yield similar results, with some covariates explaining the differences in half-life estimation between the two approaches.
The inclusion of preterm infants provided the strongest evidence of a difference, with samples from preterm infants having the highest half-lives, indicating that antibody half-life decreases with increasing duration between maternal vaccination and vaccination. delivering the baby.
Half-life estimates also varied among the three pertussis antibodies.
Furthermore, the observation that preterm infants had higher half-lives and lower decay rates of antibody titers was independent of other variables such as the choice of half-life assessment model or maternal antibody levels.
Increased infant weight was also associated with an increased rate of maternal antibody decay, suggesting a dilution effect. The elimination half-life was found to be shorter if the infant was not breastfed or was a first-born, a previous observation suggesting possible transfer of antibodies through breast milk.
Conclusions
Overall, the results showed that the two methods of estimating the half-life of maternal antibodies against pertussis antigens in infants reported similar results.
However, results from a cohort that included preterm infants showed that antibodies in preterm infants had a longer half-life and a slower decay rate than preterm infants. Longer gestational age and higher antibody levels at birth were associated with shorter half-lives.
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