Do antenatal parasite infections devalue childhood vaccination?

Abstract

On a global basis, both potent vaccine efficacy and high vaccine coverage are necessary to control and eliminate vaccine-preventable diseases. Emerging evidence from animal and human studies suggest that neglected tropical diseases (NTDs) significantly impair response to standard childhood immunizations. A review of efficacy and effectiveness studies of vaccination among individuals with chronic parasitic infections was conducted, using PUBMED database searches and analysis of data from the authors' published and unpublished studies. Both animal models and human studies suggest that chronic trematode, nematode, and protozoan infections can result in decreased vaccine efficacy. Among pregnant women, who in developing countries are often infected with multiple parasites, soluble parasite antigens have been shown to cross the placenta and prime or tolerize fetal immune responses. As a result, antenatal infections can have a significant impact on later vaccine responses. Acquired childhood parasitic infections, most commonly malaria, can also affect subsequent immune response to vaccination. Additional data suggest that antiparasite therapy can improve the effectiveness of several human vaccines. Emerging evidence demonstrates that both antenatal and childhood parasitic infections alter levels of protective immune response to routine vaccinations. Successful antiparasite treatment may prevent immunomodulation caused by parasitic antigens during pregnancy and early childhood and may improve vaccine efficacy. Future research should highlight the varied effects that different parasites (alone and in combination) can have on human vaccine-related immunity. To optimize vaccine effectiveness in developing countries, better control of chronic NTDs may prove imperative.

Figure 1. Theoretical mechanisms of reduced vaccine response in infants.

Figure 2. Typical profile of parasitic infection prevalence among pregnant women attending an antenatal clinic in coastal Kenya.

Dual infection was detected in 26% of women; three or more infections were detected in 11% of women.

Figure 3. Effect of maternal helminth infection on an infant's acquisition of protective antibodies (polyribosylribitol phosphate-specific IgG) following Haemophilus influenzae type b vaccination at 6, 10, and 14 wk of age.

Values represent geometric means (±95% confidence interval) for infants subsequently tested at 6 months of age. *p<0.001 for observed differences between the offspring of uninfected versus multiply parasitized women.