Reports

This report is based on medical evidence presented at sanctioned medical congress, from peer reviewed literature or opinion provided by a qualified healthcare practitioner. The consumption of the information contained within this report is intended for qualified Canadian healthcare practitioners only.

44th Annual Meeting of the Infectious Diseases Society of America

Toronto, Ontario / October 12-15, 2006

The success brought about by universal pediatric immunization programs is absent in adults, speakers here agreed during the scientific sessions. As reported by Dr. Gregory Poland, Professor of Medicine, Mayo Clinic College of Medicine, Rochester, New York, approximately 70,000 adults in the US die of vaccine-preventable diseases (VPDs) annually. “Mortality due to VPDs is over 100-fold greater in adults compared with children,” he told delegates. Regarding US rates of influenza coverage, for example, slightly over two-thirds of patients 65 years of age and older receive the flu shot and among those of any age with high-risk conditions, only about one-third are similarly vaccinated against the flu.

Part of the reason for poor adult immunization rates concerns a lack of funding, but as key role models in health care behaviours, “the majority of us do not get immunized, so it is no surprise our patients do not, either,” Dr. Poland noted. Recent data indicate that only about 40% of health care workers in the US are vaccinated against influenza. Poor compliance with influenza recommendations has major direct repercussions on patient health, speakers emphasized, as infected individuals start shedding influenza virus 12 to 24 hours before symptom onset, and they continue to shed four to five days after symptom onset—thereby contributing to both morbidity and mortality of patients they care for.

Adult vaccination programs are also “risk-based,” added Dr. Poland, “so if you admit to bad behaviour, we give you the hepatitis B vaccine.” With a lifetime risk of acquiring herpes zoster (HZ) at about 20%, there is ample opportunity to protect adults aged 60 years and older against HZ and its complications, he remarked. “We are an anti-vaccine culture,” Dr. Poland observed, “but you and your colleagues have a chance to demonstrate that you can—and will—do the right thing.”

Changing Attitudes

Changing patient and provider attitudes to vaccination should help broaden coverage rates, noted Dr. Kristin Nichol, Professor of Medicine, University of Minnesota, Minneapolis. For example, elderly patients may be unaware of their own risk for contracting influenza or pneumococcal disease and providers need to address that lack of awareness and strongly recommend the appropriate vaccines. Patients are often misinformed about the safety of vaccines as well, “but you cannot get the flu from the flu shot,” as Dr. Nichol stressed, and it is up to health care providers to address these unfounded fears. She also informed the audience, “Almost 100% of patients seen by medical sub-specialists as well as primary care providers are at risk of not having at least one vaccine, if not two or three, so there is a very high likelihood that patients you are seeing today have not been immunized.”

Physicians also need to recognize that even if they are extremely enthusiastic about adult vaccination, they need an organized, systematic approach to help them improve vaccination coverage rates. Issuing standing orders for nurses and other staff to both offer and give vaccines is one effective strategy known to improve coverage rates, for example. “These are safe vaccines,” confirmed Dr. Nichol, “and we do not have to be involved in assessing every individual. We need to empower the appropriate personnel to offer vaccines.”

Addressing a Wide Age Range

Among the latest of adult vaccines now approved in the US for individuals aged 60 and older is the new HZ vaccine. In the Shingles Prevention Study, approximately 38,000 patients—over half of whom were over the age of 70—received the live, attenuated, Oka/Merck varicella vaccine, “the same strain of virus used to prevent varicella in children, except it is 14 times more potent,” stated Dr. Myron Levin, Professor of Pediatrics and Medicine, University of Colorado Health Sciences Center, Denver. The primary end point of the study was the burden of illness (BOI). The BOI score represents severity of illness based on objective pain scores measured at defined intervals and plotted over time.

Results showed that the vaccine reduced the BOI score by 61.1%, at the same time reducing the incidence of both HZ infection and post-herpetic neuralgia (PHN) by 51.3% and 66.5%, respectively. Interestingly, reduction in the BOI score was somewhat lower in those older than age 69 but not significantly so. Dr. Levin remarked, “This tells us that if we do not prevent HZ in the elderly, we can still attenuate it and make the infection a milder disease.”

Duration of effect according to study results is for at least five years and maybe longer, as an ongoing study will ultimately attest. In the meantime, a significant proportion of HZ infection—along with PHN—occurs in patients between the ages of 50 and 59, “and we know that the severity of acute disease, complications and costs are similar for those between the ages of 50 and 59 as they are for those 60 and older,” Dr. Levin noted. Younger patients respond even better to the vaccine, and the vaccine has proven to be safe. Physicians therefore need to ask themselves whether younger patients may also benefit from the HZ vaccine.

Another group of potential candidates for the HZ vaccine are those who are (or will be) immunosuppressed, including patients undergoing organ transplantation, chemotherapy and patients with early HIV infection. “These patients are not yet in its licensure but nevertheless, we need to think about how we can work the vaccine in for these people as well,” Dr. Levin suggested.

In a separate presentation, a cost-effective analysis of HZ vaccine using Canadian data showed that the estimated number needed to vaccinate to prevent one case of HZ was 11, while the number needed to vaccinate to prevent one case of PHN was 43. The number needed to vaccinate to prevent pain and suffering was also extremely low at $28,000 quality-adjusted life-years gained. Findings from this analysis were especially robust, as the vaccine efficacy and duration of effect were modeled directly from the Shingles Prevention Study.

Pneumococcal Polysaccharide Vaccine

The pneumococcal polysaccharide vaccine (PPV) is currently recommended for patients over the age of 65 as well as any patient between the ages of four to 65 with conditions that heighten their susceptibility for infection. However, as argued by Dr. Daniel Musher, Professor of Medicine, Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, this is one vaccine with a mixed success story. He noted that protection against pneumococcal disease is very high in younger and healthier patients, but evidence suggests that those who need the vaccine the most are still susceptible to invasive pneumococcal disease.

The older patients are when they receive the vaccine, the less likely they are to be protected against infection; for example, an 85-year-old individual who was vaccinated five years ago is no longer protected against infection, Dr. Musher indicated.

Whether or not the protein-conjugate pneumococcal vaccine (PCPV) will offer adults additional protection is not yet established. But because the vaccine is so effective in infants, “herd immunity” may well protect adults against invasive disease. Dr. Musher cited results from a study where the incidence of invasive pneumococcal disease was reduced by at least 95% in infants who received the seven-valent pneumococcal conjugate vaccine. This dramatic reduction in invasive disease in children translated into a “striking decline” in invasive pneumococcal disease in the elderly, “so if you vaccinate one member of the herd, you are protecting the herd in general by reducing the spread of disease,” Dr. Musher explained.

Note: At the time of printing, the HZ vaccine is not available for use in Canada.