Lack of an established serologic correlate of protection for pertussis makes interpretation of pertussis antibody results problematic, but data from household contact studies support the importance of a lack of detectable antibody to either PT or PRN.18,19 Our study enrolled only term neonates, and therefore we are unable to comment on the immunogenicity and safety of the administration of the aP vaccine at birth for premature infants, in whom immune responses may be reduced. Here, F2 is linked to pertussis.