Efficacy of pneumococcal vaccine
Streptococcus pneumoniae is the most common cause of pneumonia in the elderly but it is also responsible for bacteraemia, particularly in the very young. These two studies looked at the impact of two vaccines in preventing pneumonia in the elderly and invasive disease in a younger population.
In 2000 a 7-valent polysaccharide vaccine was licensed in the USA for use in young children. The first study assessed the incidence of invasive streptococcal disease in seven regions in the USA before and after the introduction of the vaccine. The rate of invasive disease fell from 24.3 cases per 100 000 in 1999 to 17.3 per 100 000 in 2001. There was a 69% fall in the incidence in children under 2 but, interestingly, also a 32% decrease among adults aged 20–39. This was accompanied by a smaller but still significant fall in the incidence in older adults. The rate of disease caused by non-penicillin susceptible strains decreased from 6.3 per 100 000 to 4.1 per 100 000. The vaccine is decreasing the burden of invasive disease in children and possibly also in adults, perhaps by decreasing transmission. It remains to be seen whether the vaccine will be effective in slowing the emergence of resistant pneumococci or whether disease due to non-vaccine serotypes will become more common.
A 23-valent polysaccharide vaccine is recommended for those over 65 to prevent invasive disease, but it is not clear if it alters the incidence of pneumonia. The second study retrospectively assessed a cohort of 47 365 people over the age of 65 for 3 years. The primary outcomes were community acquired pneumonia (CAP) and pneumococcal bacteraemia. Receipt of the vaccine was associated with a significant reduction in the risk of bacteraemia (hazard ratio (HR) 0.56; 95% CI 0.33 to 0.93) but did not alter the risk of CAP (HR 1.07; 95% CI 0.99 to 1.14). This study supports the effectiveness of the vaccine in preventing bacteraemia but suggests that other strategies are required to combat the more common problem of pneumonia, perhaps involving the development of other vaccine formulations such as protein conjugate pneumococcal vaccines and protein vaccines.
