Pertussis has re-emerged in many western countries in recent years,
even in countries that have had high coverage vaccination programmes
for many years (1). Vaccine induced immunity to pertussis wanes, leaving
older children, adolescents, and adults susceptible to infection. Several
countries in Europe have implemented pertussis boosters in their national
immunization programmes (see 'vaccine schedules', 'pertussis', at http://www.euvac.net)
In Denmark, from 1 September 2003, the recommended vaccination at 5
years of age will include revaccination against pertussis (2). A trivalent
DTP booster against diphtheria, tetanus, and pertussis will be used.
The DTP booster contains the same amount of diphtheria and tetanus vaccines
as the DT booster (currently recommended at 5 years of age) that it
replaces, and half as much acellular whooping cough vaccine as the contents
of DTaP-IPV/ActHib used for primary immunization. The DTP booster cannot
be used for primary vaccination.
Whooping cough is endemic in Denmark, with epidemics occurring every
3-5 years. The disease is particularly serious in infants, but also
causes morbidity in older children and young people, in whom the cause
may remain unidentified. The child is well protected by primary vaccination
for some years, after which time the protection fades. Older children
who have received primary vaccination therefore risk getting whooping
cough at a later stage and constitute an infection reservoir for younger,
unprotected children. Increasing evidence indicates that adults may
also form an important reservoir and that parents may infect their own
infants (3). After revaccination with DTP booster, protection against
diphtheria and tetanus lasts at least 10 years (4). The duration of
protection against pertussis is unknown for the vaccines and schedule
in use in Denmark, but may be around 10 years as well.
From 1 July 2004, the recommended vaccination at 5 years will be further
modified to include revaccination against polio (5). The first cohort
of children not to have received OPV will reach the age of 5 years at
this time.