Rate of recurrent collapse after vaccination with whole cell pertussis vaccine: follow up study

Subjects, methods, and results

In the Netherlands over 99% of childhood vaccines are administered routinely by specialised staff within a child health clinic. All vaccinations are registered in provincial databases, so that data are accessible to medical staff if a child changes address. In 1962 an enhanced passive surveillance system for monitoring adverse events following vaccinations, with a 24 hour telephone service, was instigated. Some degree of underreporting is inevitable, but it seems to be limited and not biased against collapse (our laboratory's year report, 1994). Collapse is defined as sudden loss of muscle tone, pallor, and unresponsiveness. Sometimes symptoms are incomplete or atypical. When only one of the symptoms is present, the event is logged as an unspecified minor illness and not collapse.

In 1994, 712 adverse events were reported to the surveillance system, 587 after combined vaccination against diphtheria, tetanus, pertussis, and poliomyelitis (DTP-IPV vaccine) and Haemophilus influenzae type B (Hib-PRP-T vaccine). (The adverse events from H influenzae type B vaccine are infrequent and mild and not dealt with here.) After verification of symptoms we diagnosed 134 collapses (table).

In 1996 we followed up the 105 children with collapse reported after their first vaccinations. Detailed information about subsequent vaccinations, health state, and development in 101 of the children was supplied by child health clinics. Four of the children were lost to follow up: two had moved abroad and the names of two were unknown. The parents of one child refused further vaccinations, and 16 children completed their schedule with the combined diphtheria, tetanus, and poliomyelitis vaccine (DT-IPV). The other 84 children received further pertussis vaccine (DTP-IPV), totalling 236 doses; 74 received the full three doses. None of the children had recurrent collapse, and other adverse events were only minor. No systematic precautions were taken, although about half the children were given paracetamol prophylactically for the second vaccination; most of them did not take it for subsequent doses. At the time of follow up the children's health and development showed no particular anomalies. One child who had not received further pertussis vaccinations developed severe pertussis.

Comment

The risk of recurrent collapse is higher than the background rate, which is low for second and subsequent vaccinations, but our data show that recurrence of collapse is exceptionally low (95% confidence interval 0% to 4.3%). A scheduled case-control study of all cases reported in 1995 would add to the numbers and contribute towards an understanding of risk factors and the effect of paracetamol used prophylactically.

Our preliminary results suggest that stopping further doses of pertussis vaccine is unneccessary and that vaccinations can still take place in a child healthcare clinic without special precautions. Parents, however, do need guidance and reassurance, and vaccination as an outpatient should be considered in the few cases in which parents' fears are not allayed.