Do Pentavalent (DTwP-Hib-HBV) vaccines have sex-differential nonspecific effects? An observational study

Vaccines may alter the ability to combat infections unrelated to the target disease, i.e. have "nonspecific effects." The non-live Diphtheria-Tetanus-Pertussis vaccine (DTP) has been associated with increased child mortality, especially for females. In 2008, the DTP-containing Pentavalent vaccine replaced DTP vaccine in Guinea-Bissau. We investigate female relative to male mortality after Penta vaccination. In Guinea-Bissau, Bandim Health Project (BHP) registered children's vaccination and vital status at biannual village visits and provided vaccines. Among children Penta-vaccinated by BHP, we compared mortality of males and females in Cox proportional hazards models. Children aged 6 weeks to 8 months entered the analysis at the date of vaccination and were followed for up to 6 months. Between September 2008 and December 2017, 33,989 children aged 6 weeks to 8 months were under surveillance. Of these 12,753 (females: 6,363; males: 6,390) received Penta by the BHP and entered the study contributing with 19,667 observations. The mortality rate following Penta vaccination was 25.2 per 1,000 person years for females and 26.6 for males, resulting in an adjusted Female/Male mortality rate ratio of (F/M aMRR) 1.01 (0.82-1.25). The association between sex and mortality differed by timeliness of vaccination, F/M aMRR: 0.62 (0.41-0.93) for children vaccinated below median age, and F/M aMRR: 1.38 (0.90-2.13) for children vaccinated above median age. We did not find higher overall mortality in females than males after Penta vaccination. Our findings suggest that mortality differences between males and females following Penta vaccination may depend on timeliness of Penta vaccination.

Penta is associated with an increased female-male mortality ratio: cohort study from Bangladesh

Diphtheria-tetanus-pertussis (DTP) vaccine may be associated with excess female deaths. There are few studies of possible nonspecific effects of the DTP-containing vaccine Penta (DTP-hepatitis B-Haemophilus influenzae type b). We therefore investigated whether Penta vaccinations were associated with excess female deaths in rural Bangladesh. Between June 29, 2011 and April 20, 2016, we examined the mortality rates of 7644 children followed between 6 weeks and 9 months of age. We analyzed mortality using crude mortality rate ratio (MRR) and age-adjusted MRR (aMRR) from a Cox proportional hazards model. Mortality was analyzed according to sex, number of doses of Penta, and the order in which BCG and Penta were administered. During follow-up, 43 children died. For children who were only BCG vaccinated (BCG-only), the adjusted F/M MRR was 0.47 (0.09-2.48). However, among children who had Penta as their most recent vaccination, the adjusted F/M MRR was 9.91 (1.16-84.44). Hence, the adjusted F/M MRR differed significantly for BCG-only and for Penta as the most recent administered vaccination. Although the mortality rate was low in rural Bangladesh, there was a marked difference between adjusted F/M MRR's for children vaccinated with BCG-only compared with children where Penta was the most recent administered vaccination. Although usually ascribed to differential treatment and access to care, DTP-containing vaccines may be part of the explanation for the excessive female mortality reported in some regions.

The impact of sex hormones on BCG-induced trained immunity

The anti-tuberculosis vaccine Bacillus Calmette-Guérin (BCG) is a well-known immune modulator that induces nonspecific protective effects against heterologous infections through induction of innate immune memory, also termed "trained immunity." In randomized trials in low weight newborns, BCG vaccination reduced neonatal mortality due to decreased incidence of sepsis and respiratory infections. In many studies, sex-differential nonspecific effects of vaccines have been observed, but the mechanisms behind these differential effects are unknown. We investigated whether the important sex hormones estrogen and dihydrotestosterone (DHT) influence BCG-induced trained immunity in human primary monocytes. Although addition of estradiol and DHT to BCG inhibited the production of proinflammatory cytokines after direct stimulation of human monocytes, they did not influence the induction of trained immunity by BCG. In addition, estradiol or DHT did not induce training or tolerance in monocytes themselves. We conclude that these important sex hormones are unlikely to explain the sex-differential effects after BCG vaccination. Future studies should focus on the investigation of alternative mechanisms as an explanation for sex-differential nonspecific effects of BCG vaccination.

Heterologous ("nonspecific") and sex-differential effects of vaccines: epidemiology, clinical trials, and emerging immunologic mechanisms

A growing body of evidence from epidemiologic, clinical, and immunologic studies indicates that vaccines can influence morbidity and mortality independent of vaccine-specific B-cell or T-cell immunity. For example, the live attenuated measles vaccine and BCG vaccine may reduce mortality from infections other than measles or tuberculosis, respectively. Immunologists call these heterologous effects and epidemiologists have called them nonspecific effects, indicating that they manifest against a broad range of pathogens/disease. These effects differ by sex, can be beneficial or detrimental, and appear to be mediated by mechanisms including innate immune memory (also known as "trained immunity") and cross-reacting lymphocytes. Herein we review recent studies in this emerging field based on a meeting of experts, the recent Optimmunize meeting, held in Copenhagen, Denmark, in August 2012. Further characterization of these effects is likely to expand the way vaccines are evaluated and alter the manner and sequence in which they are given.