WHOOPING-COUGH: DIFFICULTIES IN DIAGNOSIS AND INEFFECTIVENESS OF IMMUNIZATION

Vaccination Programs for Endemic Infections: Modelling Real versus Apparent Impacts of Vaccine and Infection Characteristics

Vaccine effect, as measured in clinical trials, may not accurately reflect population-level impact. Furthermore, little is known about how sensitive apparent or real vaccine impacts are to factors such as the risk of re-infection or the mechanism of protection. We present a dynamic compartmental model to simulate vaccination for endemic infections. Several measures of effectiveness are calculated to compare the real and apparent impact of vaccination, and assess the effect of a range of infection and vaccine characteristics on these measures. Although broadly correlated, measures of real and apparent vaccine effectiveness can differ widely. Vaccine impact is markedly underestimated when primary infection provides partial natural immunity, when coverage is high and when post-vaccination infectiousness is reduced. Despite equivalent efficacy, 'all or nothing' vaccines are more effective than 'leaky' vaccines, particularly in settings with high risk of re-infection and transmissibility. Latent periods result in greater real impacts when risk of re-infection is high, but this effect diminishes if partial natural immunity is assumed. Assessments of population-level vaccine effects against endemic infections from clinical trials may be significantly biased, and vaccine and infection characteristics should be considered when modelling outcomes of vaccination programs, as their impact may be dramatic.

Pertussis: the disease and new diagnostic methods

Bordetella pertussis, the causative agent of whooping cough, produces an acute and chronic respiratory infection in infants and young children. B. pertussis is still a major health problem of young children throughout the world even though effective immunization against whooping cough is available. While predominantly a childhood disease, it has been reported also to be a cause of persistent cough in adults. This review discusses the numerous bacterial virulence factors that may play roles in the pathogenesis of pertussis and in immunity to infection. The present problems with pertussis diagnosis, recent advances, and future prospects for new and improved rapid diagnostics tests also are explored.

Bordetella pertussis whole cell vaccines--efficacy and toxicity

The literature concerning efficacy and side effects of pertussis vaccines is reviewed. With few exceptions, most vaccines induce a protective immunity lasting for 2 to 5 years. The large-scale use of pertussis vaccines has markedly contributed to the decrease in pertussis morbidity in small children but in some countries the incidence has increased in older children. Not even countries with immunisation rates of 90-95% have managed to eradicate pertussis or prevent disease in infants below the age of immunisation. The pertussis-associated mortality is currently very low in the industrialised countries and no differences can be discerned when countries with high, low and zero immunisation rates are compared. Local and benign systemic reactions are commonly seen after immunisation. The vaccines also sometimes cause convulsions, a shock-like state and, rarely, serious neurological reactions.

The epidemiology of pertussis and pertussis immunization in the United Kingdom and the United States: a comparative study

Pertussis is a common serious illness of childhood that can be controlled by immunization. It is a unique disease in that it is clinically manifested more often in females than in males. In the 20th century the mortality from pertussis has decreased steadily in both the United Kingdom and the United States. This decline in death rate was well underway prior to the introduction of pertussis vaccine but was accelerated after vaccine use became widespread. In recent years the case fatality rate in the United States has been considerably greater than that in the United Kingdom. One obvious reason for this difference is the difference in age-specific attack rates in the two nations. Available data also suggest that recent pertussis deaths in infants in England and Wales may frequently be reported as due to respiratory diseases other than pertussis. Although it is frequently suggested by some observers, there is no evidence that the incidence of pertussis was declining prior to the widespread use of vaccine. All available evidence indicates that pertussis vaccine use in both the United Kingdom and the United States was responsible for a drastic reduction in the magnitude of both endemic and epidemic pertussis. Decreased utilization of pertussis vaccine in England and Wales beginning in 1975 resulted in two major epidemics of pertussis in 1977-1979 and 1982-1983. Moderate local and systemic reactions commonly occur following pertussis immunization. These reactions appear to be less common and less severe in the United Kingdom than in the United States, but in contrast to recent studies in the United States, there are no recent quantitative studies in the United Kingdom. There are virtually no data available in the United States on the incidence of serious neurologic disease resulting from pertussis immunization. In contrast, the recently published findings of the NCES, a case-control study of national scope, have allowed attributable risk estimates of serious neurologic disease to be made. Although the NCES was a carefully controlled study, its findings in regard to attributable risk were surprisingly similar to those of several other studies in which no allowance was made for background encephalopathy due to other causes.(ABSTRACT TRUNCATED AT 400 WORDS)

Efficacy of pertussis vaccines: a brighter horizon

A study of pertussis infections in 186 children under 11 years of age in the Manchester region during 1969-71 suggests that recently-manufactured vaccines have been more effective than those made before 1967. The earlier vaccines were effective mainly against the serotypes of Bordetella pertussis possessing antigen 2, while those made from 1967 are more nearly equal in their effectiveness against thedi fferent serotypes. A booster dose of the earlier vaccines did not prevent infection with type 1,3 organisms, but we obtained a positive culture from only one child who had received four doses of recent vaccine.Simultaneous infection of a child with two or more serotypes was frequently seen. The predominant serotype in a patient was usually type 1,3; less often it was type 1,2,3 or type 1,2; it was never type 1. A change of serotype sometimes occurs during the course of the illness and is probably directed by the vaccination status of the patient in relation to the serotype of the initial infection.Our findings emphasize the need for vaccines to contain adequate amounts of all three pertussis agglutinogens, and for satisfactory immunization schedules to be used in their administration.

Efficacy of whooping-cough vaccines used in the United Kingdom before 1968. A preliminary report to the Director of the Public Health Laboratory service by the Public Health Laboratory Service Whooping-Cough Committee and Working Party

In a large survey of the efficacy of pertussis vaccines made in 33 areas in the United Kingdom during the period 1 November 1966 to 31 October 1967 a total of 3,564 households were investigated. Nine hundred and seventy-seven strains of Bordetella pertussis and 6 strains of Bord. parapertussis were isolated from persons in 792 households.After contact in the home 56% of fully vaccinated children under 5 years of age developed a paroxysmal cough, and in more than two-thirds of these patients the diagnosis was confirmed bacteriologically. This suggests that pertussis vaccination was not very effective. A comparison with the attack rate in unvaccinated children also indicates a poor protection from vaccination.NONE OF THE FOLLOWING FACTORS APPEARED TO BE RESPONSIBLE FOR THE POOR PROTECTION AFFORDED BY VACCINATION: vaccination in early infancy, a long interval since vaccination, and the absence of booster doses.Almost all the children in the survey had been given vaccines from a single manufacturer, and therefore a comparison of the efficacy of vaccines prepared by different manufacturers was inconclusive. All the vaccinated children in the survey had been vaccinated before or during 1967. The efficacy of current preparations will require to be assessed by continuing surveillance.

Advantages of aluminium hydroxide adsorbed combined diphtheria, tetanus, and pertussis vaccines for the immunization of infants

Three combined triple antigen vaccines were used to inoculate infants receiving primary immunization at 3 to 6 months of age. Laboratory potency and toxicity tests and clinical evaluation again showed that the mouse weight gain test is able to predict which vaccines will give reactions in children. The addition of aluminium hydroxide to the vaccine both increased potency and reduced the tendency to cause reactions. Assays on sera showed that almost all children produced agglutinins to Bordetella pertussis types 1, 2, and 3 when the vaccine contained aluminium hydroxide.