Is it useful to vaccinate adults with the current polysaccharide pneumococcal vaccine?

Family Pratice News,  Feb 1, 2000  

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YES

The 23-valent polysaccharide pneumococcal vaccine meets all the criteria for a useful vaccine.

It is efficacious in at least some population groups for some disease syndromes and for at least some strains of the target pathogen. It induces clinically significant protection for a limited period of time with possible revaccination, and it is cost effective. It may not be an ideal vaccine, but that doesn't mean it isn't useful for individual patients and for public health in general.

This is my view, and also the view of the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention, and of the American College of Physicians-American Society of Internal Medicine.

The 23-valent polysaccharide pneumococcal vaccine is safe. Although revaccination is associated with more arm soreness, no serious or unexpected adverse events were seen in a recent study Only 3 of 1,414 recipients sought medical care for a vaccine-associated adverse event.

Two recent randomized trials did not show that the 23-valent vaccine prevents pneumococcal pneumonia, but neither did they prove that it does not. These studies were inadequately powered and potentially misclassified cases based on upper respiratory tract culture and use of serologic tests for diagnosis. Moreover, the two studies used different populations and outcome measures, and therefore can't be compared.

But the data clearly show that the 23-valent vaccine prevents pneumoccocal bacteremia. In four epidemiologic studies--two randomized, one case-control, and one "indirect cohort" analysis--the vaccine consistently demonstrated 50%-80% efficacy in preventing invasive pneumococcal disease, depending on the population.

In the indirect cohort study, the vaccine was 75% effective in protecting against invasive disease caused by vaccine strains among immunocompetent people aged 65 and older. In the case-control analysis, protective efficacy waned with increased age and longer duration following vaccination, arguing in favor of revaccination in the elderly.

Despite the conflicting data between the pneumonia and invasive disease results, there is evidence for biological plausibility of protection with the vaccine. It's possible that opsonization and phagocytosis of pneumococci are more effective in the bloodstream than in the lungs.

The results of a 1997 cost-effectiveness analysis varied depending on which estimate for vaccine efficacy was used. However, the "worst case" analysis still gave a cost of about $26,000-$88,000 per quality-adjusted life-year for 65- to 84-year-olds. That's the same order of magnitude as many of our other interventions like mammography.

If you can prevent bacteremic disease, you prevent costs.

Dr. Benjamin Schwartz is deputy director of the epidemiology and surveillance division of the CDC's National Immunization Program, Atlanta.

NO

Support for the use of the 23-valent polysaccharide pneumococcal vaccine is unjustified at this point.

The original 12-valent vaccine was approved by the Food and Drug Administration in November 1977 based on data from two studies that were conducted in populations other than those for whom the vaccine is targeted. One was a study of over 16,000 young, healthy South African gold miners.

In January 1978, the CDC's ACIP recommended the vaccine for use in elderly people and others at high risk for pneumococcal disease, even though there were no data on its efficacy in those groups. The recommendation removed any incentive for the manufacturer to conduct such a study.

Recently a Finnish controlled trial of the 23-valent vaccine in over 26,000 people aged 65 and older showed no effect on pneumonia overall or on pneumococcal pneumonia.

When you pool the data from all the prospective trials in which patients were followed up for at least 2 years, the incidences of overall pneumonia, pneumococcal pneumonia, and pneumonia deaths are actually slightly higher with the vaccine.

Moreover, there is some evidence that the 23-valent polysaccharide may be dangerous in immunocompromised patients. In a soon-to-be-published 3-year study done in Uganda, 697 HIV-positive people aged 15-55 got the vaccine and 695 similar individuals received placebo.

Nearly twice as many vaccine recipients developed pneumonia as did the controls (90 vs. 47). This was statistically significant. The total rates of pneumococcal disease and invasive pneumococcal disease were also slightly higher among vaccine recipients.

The 23-valent polysaccharide vaccine has never been shown effective in immunocompromised patients, yet the recommendations call for them to get two doses of the vaccine, 5 years apart.

Some argue that the vaccine is cost-effective because it prevents pneumococcal bacteremia in the elderly.

Unfortunately, the 1997 cost-effectiveness analysis did not take into consideration the fact that pneumococcal pneumonia occurs at the same rate with or without use of the vaccine. The only difference is in the number of positive blood cultures. The costs for the treatment of bacteremic and nonbacteremic pneumonia are about the same.