Optimizing Health Benefits for Vaccine-Preventable Diseases
SAN DIEGO, CA—Vaccines represent the single most important medical advancement of the 20th century—saving an estimated 300 million lives. Yet vaccines now available to prevent polio, measles, influenza, varicella, and zoster remain underutilized for many reasons, three presenters told IDWeek 2012 attendees.
Despite a 99% reduction in cases of polio worldwide since 1988--when the World Health Assembly voted to eradicate the disease--eradication “is an unforgiving goal: one infection is one too many,” said Walter A. Orenstein, MD, of Emory University, Atlanta, GA. In 1988, 350,000 cases of polio were reported; that figure declined to 650 cases as of October 10, 2012.
Once endemic in 125 countries, polio is now endemic in four: Chad, Nigeria, Afghanistan, and Pakistan, with 12 other countries reporting transmission. Currently, three of six global WHO regions have been declared polio-free: the Americas, the Western Pacific, and Europe. And in 2012, India was taken off the list of endemic countries.
Two vaccines are available against polio: the oral polio vaccine (OPV), a live weakened virus, and inactivated polio vaccine (IPV), a killed virus administered by injection. Yet, “failure to vaccinate remains the biggest problem with eliminating wild viruses,” Dr. Orenstein said.
Research to help support global eradication of wild viruses includes understanding the role of IPV in conjunction with OPV to induce and boost systemic and mucosal intestinal immunity—since only when OPV is no longer used can polio truly be eliminated—and whether the use of IPV in mass vaccination campaigns will lead to decreased community immunity because of potential coverage reduction due to the use of an injectable vs an oral vaccine.
There is also the issue of cost: OPV is 15 to 16 cents per dose vs $3 per dose for IPV. New and future tools needed to finish and maintain eradication, Dr. Orenstein added, include the use of monovalent OPV, IPV, bivalent type 1 and 3 OPV, and antiviral drugs. With incidence of polio at “global record lows” and proof that “a combined global effort against a common enemy, the poliovirus, can succeed,” he noted results to date should be considered “a major victory for global health.”
With respect to measles, the global commitment and resources required are unlikely to be provided until polio has been eradicated, he said, citing “vaccine hesitancy,” which remains a major concern, particularly in the industrialized world.
Targeting Specific Groups for Influenza Vaccine
Janet A. Englund, MD, of Seattle Children's Hospital, University of Washington, focused her presentation on four groups of individuals most likely to benefit from influenza vaccination. Although current guidelines recommend that everyone over the age of 6 months be vaccinated, prioritizing who will benefit most is sometimes necessary, such as when supply is limited, she pointed out.
This year, the World Health Organization issued new prevention recommendations that prioritize pregnant women as the highest risk group and where the influenza vaccine has great potential to benefit both mother and children and risk is highest.
In Dr. Englund's opinion, her “unofficial” priority of the other risk groups should be those with high-risk conditions—such as asthma or pulmonary conditions—children, health care providers, and the elderly. Ideally, children should receive the live attenuated nasal spray influenza vaccine (LAIV), she said, which is indicated for persons 2 to 55 years of age who are generally healthy. The benefits of LAIV include that it “provides almost immediate protection and can be administered during an epidemic.” The other option for children is trivalent inactivated influenza vaccine.
She said more data are needed on efficacy of influenza vaccines, particularly in special populations; supply and distribution should be improved; and that vaccine uptake among health care workers should continue to be emphasized.
Questions Remain Surrounding Zoster Vaccine
The U.S. Food and Drug Administration licensed the zoster vaccine for the prevention of herpes zoster in immunocompetent adults aged ≥60 years in May 2006. The following October, the Advisory Committee on Immunization Practices made a provisional policy recommendation to administer a single dose of zoster vaccine to adults aged ≥60 years for the prevention of herpes zoster and postherpetic neuralgia whether or not they report a prior episode of herpes zoster, and the vaccine is incorporated into the CDC's Adult Immunization Schedule, said Michael N. Oxman, MD, of VA San Diego Healthcare System, San Diego, CA.
“However, only about 11 million doses of zoster vaccine have been distributed to date, and only about 16% of the eligible persons ≥60 years of age have been vaccinated,” he said.
The question is, why? He pointed out several reasons, including the question of safety and efficacy in the elderly as well as practical and logistical problems. Nonetheless, the pivotal trial in nearly 40,000 subjects demonstrated unequivocally that the zoster vaccine maintains its efficacy regardless of subject age. For those who did not receive the vaccine, the burden of illness was substantially greater among those 70 years of age and older.
Ongoing research will continue to explore the use of the zoster vaccine, including in immunocompromised persons and in those <60 years of age as well as the effect of simultaneous administration of zoster vaccine and other vaccines recommended for adults, such as influenza and pneumococcal vaccines.