pertussis vaccine in adolescents and only transient immunity

here is a new analysis of Tdap vaccine effectiveness (VE) in the 2012 pertussis outbreak in Washington State (see pertussis waning immunity pediatrics 2015​ in dropbox, or DOI: 10.1542/peds.2014-3358). In a case-control study of adolescents born between 1993-2000, they correlated cases of pertussis in patients who had Tdap vaccination vs controls, matched by primary provider clinic and birth year. Those born between 1993-97 had a mix of whole-cell (DTP) and acellular (Tdap) vaccines, whereas those born from 1998-2000 had only the acellular Tdap vaccines. The 2012 pertussis outbreak in Washington State included nearly 5000 reported cases, with an unexpectedly high incidence in 13-14 year olds despite the high Tdap vaccination rate of 86%. results:

--in those receiving only acellular vaccine (450 cases, 1246 controls), overall VE was 63.9% (50-74%), with
    --VE in those receiving the last Tdap within 12 months was 73% (60-82%)
    --VE in those receiving the last Tdap from 12-23 months was 54.9% (32.4-70.0%)
    --VE in those receiving the last Tdap from 24-47 months was 34.2% (-0.03-58%)
    --no difference if look at confirmed (B pertussis isolated) vs clinically-diagnosed cases
--in the older group receiving a mixture of DTP and Tdap vaccines (386 cases, 1076 controls), overall VE was 51.5% (26.1%-68.1%), with 77% having received their last Tdap at least 3 years before the outbreak (as an older cohort, they received their 11-12 yo booster longer before the epidemic). so, the authors stratified the patients by either having had the Dtap less than or more than 4 years before the outbreak and found essentially the same VE's (51.5% and 52.2% respectively for <48 months and >48 months). Given the differences in times from the last vaccination, the authors were unable to compare directly the findings between those who received the mixed vaccines vs those with only Tdap.
--there was  more protection with the Tdap brand Boostrix than Adacel, though the confidence intervals overlapped

see blog from a few months ago for a more detailed critique of the acellular pertussis component (http://blogs.bmj.com/ebm/2015/03/19/primary-care-corner-with-geoffrey-modest-md-pertussis-vaccine-not-quite-up-to-snuff/ ), though i did append it below. i also included below a couple of graphs from the CDC, the first showing the increase in pertussis since the first few years of the 2000 decade, and the second with the age distribution of cases

so, a few additional comments:
--the graphs below clearly show the dramatic increase in cases in those <1 yo, reinforcing the recommendation that pregnant women receive the Tdap vaccine during pregnancy, and the waning immunity noted above supports the recommendation that this be repeated for each pregnancy.
--the increase noted in the graph below in 7-10 year olds, a cohort that received only the acellular Tdap vaccine, also reinforces the attenuated protection, as found in this study
--the actual utility of Tdap vaccination in post-adolescence is pretty unclear. seems like there is, at best, pretty transient protection (older people have been part of the outbreaks). all of this begs for a new pertussis vaccine with improved immunogenicity and longer duration of protection (the lower incidence of pertussis found on those adolescents receiving a mixture of DTP and Tdap vaccines suggest longer-lasting VE, even though the last DTP was many years before.)

geoff

link: https://www.dropbox.com/sh/0bmvtita8mzms11/XDTwHySFFg
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from the CDC:

As of December 31, 28,660 cases of pertussis were reported to CDC during 2014, and this number is expected to increase as case counts are reconciled. This represents an 18% increase compared to the provisional numbers that were reported at the same time in 2013. The final case count in 2013 was 28,639.
Age-incidence trends observed during 2014 were similar to those in 2013 and 2012. Increased rates were again observed in adolescents 13 through 15 years of age, as well as in 16 year olds.
Overall reporting of pertussis declined during 2013 after a peak year in 2012. During 2012, 48,277 cases of pertussis were reported to CDC, including 20 pertussis-related deaths. This was the most reported cases since 1955. The majority of deaths occurred among infants younger than 3 months of age. The incidence rate of pertussis among infants exceeded that of all other age groups. The second highest rates of disease were observed in children 7 through 10 years old. Rates increased in adolescents 13 and 14 years of age

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