Estimates of influenza vaccination target population sizes in Spain for the 2006–2007 season

Abstract

This study sought to estimate influenza vaccination target population sizes in Spain for the 2006–2007 season, based firstly on current vaccine recommendations, and secondly, on the hypothetical assumption that Advisory Committee on Immunization Practices (ACIP) recommendations were to be implemented. We estimate that under present Spanish guidelines, 41% of the population should be vaccinated against influenza in the 2006–2007 season. Of those eligible for vaccination, 41% are aged ≥65 years, 16% are aged <65 years and suffer from a chronic condition, and 36% are healthy household contacts aged <65 years.

If the ACIP recommendations were implemented in Spain, the target population size would increase to 26,761,506 persons (61%), and of those eligible for vaccination, 57% would fall within the age-based recommendations (ages 6–59 months or ≥50 years), 29% would come under the healthy household contacts category, and only 5% would qualify due to suffering from a medical condition.

We thus conclude that approximately 18 million persons, 41% of the Spanish population, should receive influenza vaccination in the 2006–2007 season under present Spanish guidelines. With the estimated number of doses to be distributed during this season (10 million), compliance with current recommendations would amount to only 56% at best. Extending universal vaccination to the 50–64 age group should be considered as an option for improving influenza vaccination coverage, particularly among high-risk patients, because a greater proportion of persons would receive the recommended dose by becoming eligible for the more effective age-based strategies.

Introduction

Spain is known to have one of the highest influenza vaccination coverages in the world [1], [2]. Overall influenza vaccination coverage for the Spanish population was 20% in 2003 [3]. Nevertheless, vaccination coverages remain below desirable levels for individuals under the age of 65 years, children in particular (6%), those who suffer from a chronic condition (31%) and for health-care workers (20%) [3]. This lack of efficacy in obtaining good coverages among such subjects renders it essential to consider the possible benefit of modifying the current influenza vaccination guidelines in Spain. Before any change can be embarked upon, however, it is necessary to estimate the proportion of the Spanish population who should currently be vaccinated, and analyze how proposed changes in the recommendations would affect this proportion.

A recent paper estimated the number of people who should be vaccinated in 25 European Member States, including Spain, assuming that all the countries basically followed the Advisory Committee on Immunization Practices (ACIP) influenza vaccination recommendations [4], [5]. The specific risk groups included were: age groups under 5 years old and over 50 years old; population with medical risk factors; and health-care workers and caregivers. According to these criteria, 44% of the Spanish population should be vaccinated against influenza [4]. Healthy household contacts of high-risk persons for whom vaccine is recommended to prevent transmission were not included in the model by this study. Data from the Centers for Disease Control estimate that 73% of the 2006 US population should receive the vaccine by virtue of being persons who are at increased risk of complications or who can transmit influenza to those at high-risk, including household contacts [5], [6].

In Spain, Ministry of Health & Consumer Affairs (MHCA) influenza vaccination guidelines for the 2006–2007 season display relevant differences vis-à-vis the ACIP recommendations [5], [7]. These recommendations are shown in Table 1. In Spain, the age at which the recommendation becomes universal is 65 years, and the vaccine is not recommended for healthy young children aged 6–59 months, healthy household contacts and caregivers of such children, and healthy household contacts of persons aged ≥65 years without a medical condition [5], [7]. Spanish and US recommendations for the remaining target groups are almost identical [5], [7].

This study sought to estimate influenza vaccination target population sizes in Spain for the 2006–2007 season, based firstly on current vaccine recommendations [7], and secondly, on the hypothetical assumption that ACIP recommendations were to be implemented [5].