Conference Coverage
40th Annual Meeting of
the Infectious Diseases Society of America
http://www.medscape.com/viewarticle/443645
Oct. 28, 2002 — At the Infectious Disease Society of America (ISDA) annual meeting held in Chicago, Illinois, from Oct. 24 to 27, investigators from Israel reported on their experience with instituting hepatitis A virus (HAV) vaccination in toddlers. They found a more than 90% reduction in disease not only among the two- to four-year-olds, but in all age groups. This finding, most likely reflecting herd immunity, suggests that catch-up vaccination is not necessary.
"National anti-HAV immunization program aimed exclusively at toddlers resulted in abrupt disease reduction of >90%, not only among vaccine recipients, but also among all other age groups, by achieving high-level immunity in 2-4 year-olds, the major transmitters of HAV," write Ron Dagan, from Ben-Gurion University in Beer-Sheva, Israel, and colleagues.
From 1995 to 1998, the average incidence of HAV in Israel was 37.2 per 100,000 for Jews and 57.8 per 100,000 for non-Jews, with lifestyle differences thought to account for the differing incidences. Annual incidence decreased with increasing age.
In 1998, an inactivated HAV vaccine (Havrix) was licensed for children older than 12 months, and it became part of the routine childhood vaccination program on July 1, 1999, with two doses at ages 18 and 24 months. No catch-up program was offered, and fewer than 10% outside the target population were sporadically vaccinated. In the first semester of 2002, annual incidence dropped to less than 5 per 100,000 in all age groups.
Two other presentations at IDSA report on the success of 7-valent pneumococcal conjugate vaccine (PCV7), another example of the herd effect.
"During a period shortly after PCV7 licensure when universal vaccination of infants was likely to be incomplete, there was not only a significant decrease in invasive pneumococcal disease in young children, but also in older children and adults," write Shideh Shapinoori, from North Shore-Long Island Jewish Health System in New Hyde Park, New York, and colleagues. "These findings are compatible with herd effect."
The investigators reviewed blood and cerebrospinal fluid (CSF) isolates of S. pneumoniae at microbiology laboratories serving seven Long Island, New York, hospitals from July 1998 through April 2000, before availability of PCV7, and from July 2000 through April 2002, after routine vaccination began.
Invasive isolates were recovered from 497 patients (115 children and 382 adults). During the second time period compared with the first time period, the number of children younger than two years with invasive disease declined by 72%, and the number of invasive infections in adults decreased by 32%.
The third study, from the University of Pittsburgh in Pennsylvania, also showed a dramatic decline in invasive pneumococcal disease in children aged 3 to 36 months after implementation of a universal vaccination program.
"The availability and continued use of PCV7 should lead to even more impressive changes in the epidemiology of pneumococcal disease," the authors write.
IDSA 40th Annual Meeting: Abstracts 31, 32, 825. Presented Oct. 24-27, 2002.
Reviewed by Gary D. Vogin, MD
Laurie Barclay, MD is a staff writer with
WebMD.
Medscape Medical News is edited by Deborah Flapan, a news coordinator at Medscape. Send press releases and comments to news@webmd.net.
Medscape Medical News 2002. © 2002 Medscape
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