To set the record straight, North American Vaccine Inc.and the National Institute of Child Health and HumanDevelopment (NICHD) have issued statements clarifyingtheir original announcement of results in their pivotalPhase III pertussis vaccine trial. (See BioWorld Today,Nov. 28, 1994, p. 4.)

On Tuesday, Nov. 22, NICHD released the "promising"data obtained from its randomized, double-blinded,placebo-controlled trial in Gotebord, Sweden of anacellular, single-antigen pertussis vaccine. Its pressstatement reported that "the vaccine demonstrated anefficacy of 71 percent in protecting infants in the studycohort from contracting pertussis."

In a different context, the release mentioned that"incidence of all side effects . . . was far below thatreported when infants receive the currently-used whole-cell vaccine."

These two unrelated items flooded the agency'sswitchboard with "a lot of calls from press, the generalpublic and a lot of investment houses," said the NICHDchief of research reporting, Michaela Richardson.

"People had found out on their own," Richardson toldBioWorld Today, "because it's widely reported in theliterature, that the generally accepted efficacy rate forwhole-cell pertussis vaccine is about 80 percent. Therewas so much confusion as to what was meant by`efficacy,' and so many people trying to compare it [theexperimental acellular vaccine] to the efficacy rate for thewhole-cell version," that NICHD issued a clarificationlast Wednesday.

It stated that attempts to compare the stated 71 percentefficacy of the acellular form with whole-cell "areinappropriate because whole-cell pertussis vaccine hasnever been examined in such a stringent manner. Inaddition," the clarification emphasized, "the NICHDstudy is the first report of the protection afforded in arandomized, double-blind, placebo-controlled trial of anypertussis vaccine, whole-cell or acellular, whenadministered to infants at three, five and 12 months ofage."

"In retrospect," Richardson said, "we should haveincluded the definition of `efficacy' in our first pressrelease. We just assumed it's one of the things that peopleknow. "The brief clarifying follow-up statementdescribed efficacy as "the proportion of disease preventedby a vaccine. For example, in a group of 1,000unvaccinated children, if you suspect 50 cases ofpertussis per year, vaccinating with a vaccine of 71percent efficacy would reduce the number of cases to 15."

"Needless to say," North American Vaccine's press-relations spokeswoman, Kelley Jenkins, told BioWorldToday, "we moved on to what we thought would be aclearer clarification."

In its own follow-up press release, North AmericanVaccine plugged in the actual efficacy numbers from theSwedish trial in place of NICHD's theoretical example."Concerning the vaccine's efficacy," it stated, "thecompany's DTaP [diphtheria-tetanus-pertussis] vaccinereduced the incidence of typical whooping cough fromapproximately 14 percent in the untreated control group[of 1,687 infants] to approximately four percent in thegroup [of 1,692] that received the DTaP."

Of those 1,687 controls _ given diphtheria and tetanusimmunization, but not pertussis _ 240 (i.e., 14 percent)came down with whooping cough, compared with only72 cases in the study group of 1,692 (4 percent). n

-- David N. Leff Science Editor

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