Persistence of antibody response to pneumococcal capsular polysaccharides in vaccinated long term-care residents in Brazil

Abstract

To evaluate the immunogenicity of 23-valent pneumococcal polysaccharide vaccine in 52 nursing homes residents aged ≥ 60 years, IgG antibodies to serotypes 1, 5, 6B, and 8 were measured by ELISA and compared before, and 1 and 12 months following vaccination. A significant immunological response for all serotypes was observed at 1 month after vaccination. The mean increase in antibody concentration was highly variable and ranged from 1.6 to 2.7. After 1 year, the mean concentrations remained significantly higher than prior to vaccination for serotypes 1, 6B, and 8, although there was a decrease in all mean IgG concentrations. Antibody levels were higher in men than in women, before and after immunisation. Post-vaccination values tended to be lower among subjects aged >75 years. Reduction in IgG concentrations by 33% 1 year after vaccination suggests that revaccination of institutionalised elderly people may be needed.

Introduction

Disease by Streptococcus pneumoniae is associated with a significant degree of morbidity and mortality and represents a substantial economic burden on society [1], [2]. Older persons as well as young children and the immunocompromised are at increased risk for invasive pneumococcal disease [3], which is generally much more severe and life-threatening for the elderly [1], [4], [5], [6]. The risk is further increased among older adults living in long-term care institutions, where pneumococcal outbreaks may occur [7], [8], [9].

Vaccination is an important strategy to help prevent disease progression given that early mortality from bacteraemic pneumococcal pneumonia may occur despite appropriate penicillin treatment [10], and that increasing rates of multi-drug resistant strains are a source of concern for the management of pneumococcal infections [4], [11].

The 23-valent pneumococcal polysaccharide vaccine (PPV) has been available since 1985, but its use among older persons has been limited, due in part to uncertainties about its benefits [6], [12]. Although substantial antibody response can be found among the elderly, it may decrease with advancing age [9]. Moreover, the duration of immunity is not exactly defined [6]. To date, there is strong evidence that PPV is effective in preventing invasive disease [1] and in reducing hospitalisation for pneumonia, pneumococcal bacteraemic disease and hospital deaths with pneumonia among elderly people [12].

In Brazil, PPV was included for the first time in the national immunisation campaign for the elderly, in 1999. It was offered free for persons aged ≥60 years, who were (i) hospitalised or institutionalised; (ii) with diabetes mellitus or chronic heart, lung, spleen, or kidney illnesses; (iii) with malignancy, human immunodeficiency virus infection or to transplant recipients [13]. No study has been published concerning the immunological response of institutionalised older subjects in Brazil. To evaluate the immune response and its persistence in high-risk older residents of nursing homes, we prospectively measured and compared the concentrations of IgG antibodies to four pneumococcal capsular polysaccharides (PPSs) prior to and 1 and 12 months following PPV administration.