n engl j med 368;6 nejm.org february 7, 2013
mation as well as results entries and publication
information. We think that trial-registration num-
bers should be used in all documentation for
referencing clinical trials to mitigate potential
confusion about the study under consideration.
Deborah A. Zarin, M.D.
Tony Tse, Ph.D.
National Library of Medicine
Dr. Zarin reports being the director of and Dr. Tse reports
being a program analyst at ClinicalTrials.gov of the National
Library of Medicine, National Institutes of Health. No other po-
tential conflict of interest relevant to this letter was reported.
Editor’s note: Zarin and Tse are correct. It is our pol-
icy to refer to clinical trials by their registration
number or to reference a publication in which they
can be unequivocally identified, and we should have
done so for the ones they mentioned in their letter.
1. Colman E, Golden J, Roberts M, Egan A, Weaver J, Rose-
braugh C. The FDA’s assessment of two drugs for chronic weight
management. N Engl J Med 2012;367:1577-9.
2. FDA briefing document — lorcaserin hydrochloride tablets,
10 mg. Presented at the Endocrinologic and Metabolic Drugs Ad-
visory Committee meeting, May 10, 2012 (http://www.fda.gov/
3. FDA briefing document: phentermine/topiramate. Presented
at the Endocrinologic and Metabolic Drugs Advisory Committee
meeting, February 22, 2012 (http://www.fda.gov/downloads/
4. Lorcaserin trials. ClinicalTrials.gov (http://clinicaltrials.gov/
5. Phentermine/topiramate trials. ClinicalTrials.gov (http://
Priming with Whole-Cell versus Acellular Pertussis Vaccine
To the Editor: From January through August
2012, Oregon had its highest annual tally of re-
ported pertussis cases since 1959. The incidence
was highest among infants and children between
10 and 14 years of age. Increasing disease among
school-aged children despite high vaccination
coverage may be in part a consequence of using
acellular pertussis vaccines (diphtheria–tetanus–
acellular pertussis, or DTaP), which in 1997 were
approved and recommended for all childhood
series instead of whole-cell pertussis vaccines
(diphtheria–tetanus–whole-cell pertussis, or
DTwP).1 We wanted to examine the effectiveness
of first-dose DTwP priming in children fully im-
munized with DTaP beyond their first year of life
and in those who subsequently received a tetanus–
diphtheria–acellular pertussis (Tdap) booster.
Pertussis cases from statewide surveillance
and immunization records from Oregon’s popu-
lation-based immunization information system,
ALERT IIS, were reviewed for children born in
Oregon in the years 1997 through 1999. Cases
included all patients considered to have “con-
firmed” pertussis as defined by the Council of
State and Territorial Epidemiologists.2 The inci-
dence of disease among children who initially
received an acellular vaccine was compared with
that among children who initially received a
whole-cell vaccine in the context of a variety of
pertussis vaccination scenarios.
ALERT IIS holds pertussis immunization
records for 195,959 children born from 1997
through 1999. From April 1997 through July
2012, a total of 484 cases of pertussis were re-
ported, of which 402 (83%) could be matched to
ALERT IIS pertussis vaccination records; 346 of
these children had been vaccinated 14 days or
more before disease onset. In all scenarios, the
reported rates of pertussis were significantly
lower among children who had started the vac-
cination process with DTwP than among those
who had started with DTaP (Table 1). This effect
existed regardless of whether the pertussis vac-
cination series had been completed or a recent
Tdap booster dose had been administered. The
risk of pertussis in the cohorts diverged at
10 years of age.
Among children born during the 1997–1999
transition period, those who underwent priming
with acellular rather than whole-cell pertussis
vaccine had higher rates of reported pertussis.
Our findings concur with those from Australia
and are consistent with the recent epidemiologic
reports on pertussis in the United States.3,4 Al-
though statewide surveillance data underestimate
disease incidence, and population-based immu-
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