SUBCLINICAL PERTUSSIS IN INCOMPLETELY VACCINATED AND UNVACCINATED INFANTS

Incidental to a phase II study of acellular and whole-cell pertussis v accines involving 342 infants who were clinically observed from birth until the age of 9 months, subclinical pertussis was retrospectively d iagnosed iii 10 infants on the basis of serological evidence, IgG and IgA to filamentous haemagglutinin (FHA), pertussis toxin (PT) and aggl utinogens 2 and 3 (AGG2,3) were assayed by enzyme-linked immunosorbent assay (ELISA) in serum obtained at birth and at 2, 4, 6 and 9 months of age, All 10 infants had greater than or equal to 4-fold rises in at least two different pertussis IgG antibodies, Nine of the 10 infants had greater than or equal to 4-fold increases in all three IgG antibod ies measured: One infant had greater than or equal to 4-fold increases in IgG-FHA and IgG-AGG2,3 but not IgG-PT. Seven infants had raised Ig A antibodies to PT and FHA and 4 infants had raised IgA antibodies to AGG2,3, Subclinical infection provoked differing degrees of antibody p roduction in response to multiple antigens, Subclinical infection was detected in both unvaccinated infants (4) and in infants who had been vaccinated from 2 months of age with either acellular (4) or whole-cel l Vaccines (2), Subjects were 8 months of age or younger and only 1 ha d completed primary vaccination, Other infections of infancy were comm only detected; 4 infants had upper respiratory disease about the time of subclinical pertussis, None had a household member with symptomatic pertussis. Likelihood of subclinical infection was related to signifi cantly lower levels of maternally acquired pertussis IgG-AGG2,3 antibo dies but not associated with infants' nutritional status, Subclinical pertussis is described in very young babies at an age when the disease is most severe, and therefore has implications for infant morbidity a nd mortality; it is also relevant to disease surveillance and vaccine efficacy studies.