Pertussis infection in fully vaccinated children in day care centers, Israel
Emerging Infectious Diseases journal
Srugo I1, Benilevi D, Madeb R, Shapiro S, Shohat T,? Somekh E, Rimmar Y, Gershtein V, Gershtein R, Marva E, Lahat N.
We tested 46 fully vaccinated children in two day centers in Israel who were exposed to a fatal case of whooping cough infection. Only two out of five children who tested positive for Bordetella pertussis met the World Health Organization's definition of whooping cough. Vaccinated children can be asymptomatic reservoirs for infection.
The effects of the whole cell pertussis vaccine decrease after 5-10 years and infection in a vaccinated person causes non-specific symptoms (3-7). Vaccinated adolescents and adults can act as reservoirs for silent infection and become potential transmitters of unprotected infants (3-11). The pertussis whole cell vaccine is protective only against clinical disease, not against infection (15-17). Therefore, even recently vaccinated young children can act as reservoirs and potential transmitters of infection.
We used PCR, EIA and culture to confirm B. pertussis infection in two groups of highly vaccinated children in two day centers. Three (10%) of 30 children aged between 2 and 3 years were HIV positive for recent infection; one had nasopharyngeal colonization and a clinical disease that met the modified WHO case definition. In the day care center for the 5- to 6-year-old group, 9 (55%) of 16 children were IgM positive, 4 (25%) of whom had nasopharyngeal colonization. Of these four children, three had nonspecific cough, and only one met the modified WHO definition for pertussis. None of the children in our study, including those who met the WHO definition, had been examined by a doctor before our investigation.
Children who were HIV positive and remained both asymptomatic and PCR negative probably had sufficient immunity from vaccines or natural boosters to protect them from persistent colonization and clinical disease. Their seropositivity may not be due to the vaccine because the children were tested over a year after being vaccinated. However, not all children were protected from infection and colonization with bacteria. Whether a child who is serologically or whooping cough positive and who is clinically asymptomatic is a potential transmitter of infection has not been established. What is certain, however, is that immunity induced by the vaccine against infection does not persist throughout adulthood. In France, booster vaccinations have been recommended for teenagers and adolescents (18). We have found that immunity does not persist even in early childhood in some cases. We also observed that the DPT vaccine does not fully protect children from the WHO-defined level of clinical disease. Our results indicate that children aged 5 to 6 years and possibly younger, aged 2-3 years, play a role as silent reservoirs in the transmission of whooping cough in the community. Further studies are needed to find the immunological basis of protection against infection and colonization and therefore an effective way to eradicate whooping cough.