Parasitic infection inhibited vaccine
response in children from rural Kenya
PHILADELPHIA — New data from Kenya indicate that there is an
under-recognized burden of parasitism in younger children that may be linked to
a decreased response to standard childhood vaccinations, according to a
presenter here at the American Society of Tropical Medicine and Hygiene 60th
Children are at high risk for soil-transmitted helminths (STHs) and
protozoal infections, and these parasitic infections have detrimental effects
on weight, height and head circumference growth rates in children aged 0 to 36
months. Certain parasitic infections during childhood may also be linked to
decreased response to standard childhood vaccinations, according to results of
a study by A. Desiree LaBeaud, MD, MS, of the Children’s Hospital
Oakland Research Institute in California, and colleagues.
“Vaccines are among the most cost-effective strategies for
infectious disease prevention in the world. But unfortunately, there is a
disparity, and children in developing nations are often much less responsive to
vaccinations compared with their counterparts in developed nations,”
LaBeaud said during a presentation. “While there are many reasons for
this, including cold chain issues, infrastructure, HIV/AIDS and malnutrition,
chronic parasitic infection plays a role in weakened vaccine response.”
To document the prevalence of parasites and their effects on growth and
response to childhood vaccines in young children in coastal Kenya, the
investigators collected stool, urine and blood samples from children at 6-month
intervals until age 3 years and tested for STHs (Ascaris, Trichuris,
hookworm and Strongyloides), protozoa (malaria, Giardia) and
schistosomiasis. Height, weight and head circumference were measured at each
visit. A total of 545 infant–maternal pairs were enrolled in the study
that began in 2007, and infections in both mothers and infants were documented.
Of 545 children, 32% were infected with one parasite, and 8% of the
children were infected with more than one parasite. Hookworm was the most
prevalent STH (11%), followed by Trichuris (10%), Ascaris (4%)
and Strongyloides (2%). Giardia was the most prevalent protozoan
(13%), followed by malaria (12%). Immunoglobulin G4 testing revealed that 4% of
the children had schistosomiasis.
“There are children who have more than one parasitic infection as
early as in the first 6 months of life and this polyparasitized proportion
increases as the child cohort gets older,” LaBeaud said.
According to LaBeaud, polyparasitized children were more likely to have
polyparasitized mothers (P=.006) and have poor HC growth rate (0.002).
Children with malaria (P=0.04or Trichuris infection
(P=.005) had lower weight z scores, and children with any
parasitic infection (P=.01) had lower HC z scores.
All of the children in the study received a complete vaccination series,
which includes a pentavalent vaccine (hepatitis B, Haemophilus
influenzae type b, tetanus-diphtheria and whole-cell pertussis) and
trivalent oral polio vaccine. Pentavalent vaccine was given at 6, 10 and 14
weeks of age, and polio vaccine was given at 0, 6, 10 and 14 weeks of age.
Regarding vaccine response, children with STH had statistically
lower tetanus, Hib, and diphtheria titers compared with uninfected children.
Children with malaria had statistically lower polio, tetanus, and diphtheria
Response to tetanus, diphtheria, hepatitis B virus, Hib and poliovirus
vaccinations were measured by standard enzyme-linked immunosorbent assay
(ELISA). McNemar’s test, t test on log-transformed titers and
repeated measure modeling were used to analyze data.
Disclosure: Dr. LaBeaud reports no relevant financial
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