Open Access
Abstract
As part of the vaccination activities against influenza A[H1N1]pdm vaccine in 2009–2010, countries in Latin American and the Caribbean (LAC) implemented surveillance of events supposedly attributable to vaccines and immunization (ESAVI). We describe the serious ESAVI reported in LAC in order to further document the safety profile of this vaccine and highlight lessons learned.
We reviewed data from serious H1N1 ESAVI cases from LAC countries reported to the Pan American Health Organization/World Health Organization. We estimated serious ESAVI rates by age and target group, as well as by clinical diagnosis, and completed descriptive analyses of final outcomes and classifications given in country.
A total of 1000 serious ESAVI were reported by 18 of the 29 LAC countries that vaccinated against A[H1N1]pdm. The overall reporting rate in LAC was 6.91 serious ESAVI per million doses, with country reporting rates ranging from 0.77 to 64.68 per million doses. Rates were higher among pregnant women (16.25 per million doses) when compared to health care workers (13.54 per million doses) and individuals with chronic disease (4.03 per million doses). The top three most frequent diagnoses were febrile seizures (12.0%), Guillain-Barré Syndrome (10.5%) and acute pneumonia (8.0%). Almost half (49.1%) of the serious ESAVI were reported among children aged <18 years of age; within this group, the highest proportion of cases was reported among those aged <2 years (53.1%). Of all serious ESAVI reported, 37.8% were classified as coincidental, 35.3% as related to vaccine components, 26.4% as non-conclusive and 0.5% as a programmatic error.
This regional overview of A[H1N1]pdm vaccine safety data in LAC estimated the rate of serious ESAVI at lower levels than other studies. However, the ESAVI diagnosis distribution is comparable to the published literature. Lessons learned can be applied in the response to future pandemics.
Keywords
- Events supposedly attributable to vaccines and immunization;
- Vaccine safety;
- Guillain-Barré;
- Febrile seizures;
- Pandemic influenza;
- H1N1
1. Introduction
In recent years, there has been rapid uptake in seasonal influenza vaccination in the Americas; prior to the emergence of the influenza A (H1N1) virus, 35 out of 46 countries and territories had introduced the seasonal vaccine, compared to 13 countries and territories in 2004 [1]. Common target populations included the elderly, children, and individuals with chronic disease [1] and [2]. As the use of seasonal influenza vaccine expanded, so too did the surveillance capacity to monitor Events Supposedly Attributable to Vaccination or Immunization (ESAVI); this terminology is commonly used in Latin America and the Caribbean (LAC) and is defined as a clinical condition following vaccine administration, which may or may not be related to the vaccination and which causes great concern among the population [3]. In most countries, ESAVI surveillance is passive and based on voluntary and spontaneous reports from health providers [4].
In June 2009, Dr. Margaret Chan, Director General of the World Health Organization (WHO), declared that circulation of influenza A (H1N1) had reached pandemic levels [5]. From the pandemic's onset, there were particular concerns about A[H1N1]pdm vaccine safety, despite the proven safety of the seasonal vaccine [6]. Concerns were centered around the short time frame available for A[H1N1]pdm vaccine production, manufacturers’ use of novel adjuvants (AS03, MF59), and the antecedent temporal association of a previous influenza vaccine with Guillain-Barré Syndrome (GBS) in the 1970s [7] and [8].
LAC countries and territories administered approximately 144.6 million doses of A[H1N1]pdm vaccine in a series of national campaigns, placing LAC as one of the regions with the highest number of doses administered [9]. Campaign timing was based on the availability of vaccine at the national level, which differed country to country; however, with the exception of Venezuela, all vaccination campaigns in LAC occurred between December 2009 and September 2010. Venezuela vaccinated and reported after this period. This paper describes serious ESAVI reported in LAC following A[H1N1]pdm emergency vaccination to further document the vaccine's safety profile and its implications for national immunization programs (NIPs), as well as highlights lessons learned
