More than prevention
Although vaccines usually make us think of preventing illness, many vaccines reduce the severity of disease rather than preventing it. Examples include vaccines for malaria and shingles. "That doesn't mean these vaccines are ineffective," says Dr. Jennie Johnstone, a clinical research fellow in infectious diseases at the University of Alberta. "Immunized people who contract the disease are likely to be less sick and [will tend to] avoid long-term health consequences."
A case in point is the vaccine for Streptococcus pneumoniae, the most common cause of community-acquired pneumonia (the name given to pneumonia acquired outside of a hospital setting). This type of pneumonia occurs throughout the world and is a leading cause of illness and death. The adult pneumococcal vaccine has been available since the mid-1980s. Research evidence shows that, although the vaccine does not prevent pneumonia, it does reduce the rate of invasive pneumococcal diseases (such as pneumococcal meningitis, an infection of the membranes covering the brain and spinal cord) and pneumococcal bacteremia (a blood infection). Dr. Johnstone set out to investigate a new hypothesis: that prior vaccination might improve outcomes in patients who develop pneumonia.
She worked with a very large database-approximately 3,400 adults with community-acquired pneumonia who were admitted to the six Capital Health hospitals in the Edmonton region between 2000 and 2002. Statistical methods were used to determine the association between prior vaccine use and outcome. Vaccinated patients with community-acquired pneumonia had a death rate and a rate of admission to the intensive-care unit that were both about 40% lower than those of patients who had not been vaccinated.
"It's very clear: the people who were vaccinated had much better outcomes," says Dr. Johnstone. "The results indicate we could be doing better for many more patients, since only 22% of our population were vaccinated before their hospitalization. Moreover, fewer than 10% of eligible patients were vaccinated before they were discharged from hospital." Current guidelines recommend the vaccine for anyone at increased risk for pneumonia, including those 65 and older, people with cardiovascular and lung diseases, and those whose immune systems are not functioning correctly.
"Now I can say with confidence to my infectious-disease colleagues that this is a very worthwhile vaccine. The perception that it is ineffective is wrong. The vaccine needs to be promoted-to get vaccination rates up to where they should be."
The pneumonia study was Dr. Johnstone's first foray into epidemiology, the study of factors affecting the health and illness of populations. In the fall, she hopes to begin working toward a master's degree in epidemiology at McMaster University in Ontario. "The degree will give me the tools I need to start a serious program of epidemiological research. Eventually I'd like to combine clinical work and research, hopefully back in Alberta."