BALTIMORE — The herpes zoster vaccine is as immunogenic in adults aged 50–59 as it is in those aged 60 and older, Santosh C. Sutradhar, Ph.D., reported at a conference on vaccine research sponsored by the National Foundation for Infectious Diseases.
Zostavax, manufactured by Merck & Co., was licensed by the U.S. Food and Drug Administration in May 2006 for the prevention of herpes zoster in adults aged 60 and older only. Merck had sought an indication for those aged 50–59 years, but an earlier FDA advisory panel had recommended against it because data on safety and efficacy in that age group were lacking, as were overall data on duration of immunity for the vaccine.
In October 2006, the Advisory Committee on Immunization Practices recommended universal use of Zostavax among adults aged 60 and older.
Nonetheless, epidemiologic data suggest that the annual risk of developing herpes zoster actually begins to increase markedly around age 50 years and rises sharply afterward. Thus, “it is important to assess the immunogenicity and safety of Zostavax in this age group,” said Dr. Sutradhar, senior biometrician at Merck & Co., West Point, Pa.
In combined data from two protocols that had been presented separately to the FDA, the vaccine was administered to 389 subjects aged 50–59 and to 733 aged 60 and older. Of those, 377 and 731, respectively, completed the 28-day follow-up. Antibody response, assessed by geometric mean fold rise of varicella zoster virus antibody from prevaccination to 4 weeks post vaccination, was increased substantially in both groups, by 2.6 in the younger group, compared with 2.3 in the older subjects.
Both of those levels exceeded the predefined threshold for “acceptable” antibody response, and the response for the younger group met the “noninferiority” criteria, compared with that of the older group, he said.
Adverse events within 28 days following vaccination were more common in the 50- to 59-year-olds, with 60% reporting one or more total adverse events, compared with 44% of the 60-plus group. Vaccine-related adverse events were reported by 52% and 35%, respectively. Injection-site reactions were the most common of these, reported by 50% of the younger subjects and 34% of the older ones. Systemic vaccine-related adverse events were far less common, reported by 6% and 3%, respectively, and no subject in either age group reported any serious vaccine-related adverse events.
Merck is working with the FDA to develop a protocol that will provide vaccine efficacy data as well as additional safety data specifically for the 50- to 59-year-old age group, as had been done previously with those aged 60 and older in the Shingles Prevention Study (SPS). Those findings, from more than 38,000 adults older than 60, showed that the vaccine reduced the burden of illness related to herpes zoster pain, the incidence of postherpetic neuralgia, and the incidence of herpes zoster (N. Engl. J. Med. 2005;352:2271–84).
Merck hopes to launch the new protocol sometime this year, according to a company spokeswoman.