Elsevier

Vaccine

Volume 28, Issue 18, 19 April 2010, Pages 3127-3133
Vaccine

Surveillance for adverse events after DTwP/Hib vaccination in Brazil: Sensitivity and factors associated with reporting

https://doi.org/10.1016/j.vaccine.2010.02.059Get rights and content

Abstract

We estimated the sensitivity, i.e., the proportion of all cases of adverse events following immunization (AEFIs) reported to the Brazilian passive surveillance for adverse events following immunization (PSAEFI) with the diphtheria-tetanus-whole-cell pertussis-Haemophilus influenzae type b (DTwP/Hib) vaccine, as well as investigating factors associated with AEFIs reporting. During 2003–2004, 8303 AEFIs associated with DTwP-Hib were reported; hypotonic-hyporesponsive episodes (HHEs), fever and convulsions being the most common. Cure without sequel was achieved in 98.4% of the cases. The mean sensitivity of the PSAEFI was 22.3% and 31.6%, respectively, for HHE and convulsions, varying widely among states. Reporting rates correlated positively with the Human Development Index and coverage of adequate prenatal care, correlating negatively with infant mortality rates. Quality of life indicators and the degree of organization of health services are associated with greater PSAEFI sensitivity. In addition to consistently describing the principal AEFIs, PSAEFI showed the DTwP/Hib vaccine to be safe and allayed public fears related to its use.

Introduction

In recent decades, vaccination has become an essential component of public health programs and is a decisive factor in controlling numerous infectious diseases [1]. In Japan, Sweden and England and Wales [2], a drastic reduction in the incidence of vaccine-preventable diseases has increased the perceived risk of adverse events following immunization (AEFIs), which has resulted in lower vaccination coverage [1], [2].

As early as the 1980s, concerns raised by this situation prompted countries such as United States, Canada, Cuba, India and New Zealand as well as European Union Member States to implement surveillance for adverse events following immunization (SAEFI) [3], [4], [5], [6], [7], [8]. In 1999, the World Health Organization (WHO) created the Global Advisory Committee on Vaccine Safety, which enables the WHO to respond promptly to issues of vaccine safety, as well as to assess the implications of vaccine safety for practice worldwide and for WHO policies [9], [10], [11].

In Brazil, passive surveillance for adverse events following immunization (PSAEFI) was implemented in 1984 and was initially restricted to the state of São Paulo [12]. Under the guidance of the National Immunization Program (NIP), PSAEFI coverage became nationwide in 1998 [13]. The Brazilian PSAEFI has since been the object of studies focusing on specific regions or types of events [12], [14], [15], [16]. However, to date, there have been no studies evaluating its features and performance at the national level.

Due to its simplicity, its lower cost and its capacity to reach a broad population base, passive surveillance is the strategy of choice for monitoring vaccine safety profiles [3]. However, one of its major drawbacks is its low sensitivity (i.e., the high rates of underreporting of AEFIs) [3], which has a negative impact on its power to describe AEFIs and to identify rare or unknown events [17]. Therefore the sensitivity of a passive surveillance is an important indicator to assess of its usefulness [17].

The study undertaken by Martins et al. [13] focusing the safety of the combined diphtheria-tetanus-whole-cell pertussis and Haemophilus influenzae type b (DTwP/Hib) vaccine, which was included in the routine Brazilian vaccination in 2002 [18], provided us with gold standard to estimate the sensitivity of Brazilian PSAEFI associated with DTwP/Hib. Since hypotonic-hyporesponsive episodes (HHEs) and convulsion are the most common severe AEFIs reported in Brazil, we chose those events as the main focus of our study.

The objectives of this study were to estimate the sensitivity of the Brazilian passive SAEFI, focusing on AEFIs associated with DTwP/Hib vaccination among infants less than one year of age, to investigate factors associated with reporting and to evaluate the consistency of the PSAEFI in describing the principal characteristics of AEFIs.

Section snippets

Methods

This was a descriptive study in which the population of interest was that of infants less than one year of age receiving at least one dose of the DTwP/Hib vaccine during the 2003–2004 period, at any vaccination site in Brazil.

The study area included all 26 states of Brazil and the Federal District of Brasília. Brazil is the largest country in Latin America, with a territory of approximately 8.5 million km2 and a population of approximately 190 million. The estimated mean population of infants

Results

The total number of doses administered in the 2003–2004 period was 18.7 million [22]. During that same period there were 9656 AEFIs associated with DTwP/Hib vaccine reported in infants less than one year of age. Of those, 1242 were excluded: 706 for being duplicate records (typically cases reported by primary health care unit at witch the children had been vaccinated and by hospital at witch the children had been treated), and 536 for being also associated with vaccines other than the DTwP/Hib

Discussion

The PSAEFI in Brazil has certain features that distinguish it from similar systems in developed countries such as the United States and those in the European Union [4], [26]. Their objectives are less comprehensive, and have operated exclusively under the auspices of the NIP [12], [24] and are not formally linked to a regulatory health agency. Nevertheless, a committee, created in 2008, has been charged with fostering joint activities and promoting cooperation between NIP and the regulatory

Acknowledgements

The authors are grateful to all of the staff of the NIP and to Dr. Luiza de Marilac Meirelles Barbosa in particular.

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