Potential carrier priming effect in Australian infants after 7-valent pneumococcal conjugate vaccine introduction.
OBJECTIVE
To investigate evidence of clinical protection in infants after one dose of 7-valent pneumococcal conjugate vaccine (7vPCV) owing to carrier priming.


METHODS
Using Australian National Notifiable Diseases Surveillance System data, we conducted a descriptive analysis of cases of vaccine type invasive pneumococcal disease (VT-IPD) during "catch-up" years, when 7vPCV was carrier primed by prior administration of DTPa vaccine. We compared the number of VT-IPD cases occurring 2-9 wk after a single dose of 7vPCV (carrier primed), with those < 2 wk post vaccination, when no protection from 7vPCV was expected yet. Further comparison was conducted to compare the occurrence of VT-IPD cases vs non-VT-IPD cases after a single carrier-primed dose of 7vPCV.


RESULTS
We found four VT-IPD cases occurring < 2 wk after one carrier primed dose of 7vPCV while only one case occurred 2-9 wk later. Upon further comparison with the non-VT-IPD cases that occurred after one carrier primed dose of 7vPCV, two cases were detected within 2 wk, whereas seven occurred within 2-9 wk later; suggesting a substantial level of protection from VT-IPD occurring from 2 wk after carrier-primed dose of 7vPCV.


CONCLUSIONS
This data suggest that infants may benefit from just one dose of 7vPCV, likely through enhanced immunity from carrier priming effect. If this is proven, an adjusted 2-dose schedule (where the first dose of PCV is not given until after DTPa) may be sufficient and more cost-effective.
Mohamed Tashani, Sanjay Jayasinghe, Harunor Rashid, Robert Booy, National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, the Children's Hospital at Westmead, Sydney 2145, Australia.
Mohamed
M
Tashani
Mohamed Tashani, Sanjay Jayasinghe, Harunor Rashid, Robert Booy, National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, the Children's Hospital at Westmead, Sydney 2145, Australia.
Sanjay
S
Jayasinghe
Mohamed Tashani, Sanjay Jayasinghe, Harunor Rashid, Robert Booy, National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, the Children's Hospital at Westmead, Sydney 2145, Australia.
Zitta B
ZB
Harboe
Mohamed Tashani, Sanjay Jayasinghe, Harunor Rashid, Robert Booy, National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, the Children's Hospital at Westmead, Sydney 2145, Australia.
Harunor
H
Rashid
Mohamed Tashani, Sanjay Jayasinghe, Harunor Rashid, Robert Booy, National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, the Children's Hospital at Westmead, Sydney 2145, Australia.
Robert
R
Booy
Carrier priming; Conjugate vaccine; Infant; Invasive pneumococcal disease