Pertussis: herd immunity and vaccination coverage in St Lucia
Cooper, E.; Fitch, L.
Lancet 2(8359): 1129-1132
1983
ISSN/ISBN: 0140-6736 PMID: 6138654 DOI: 10.1016/s0140-6736(83)90637-2Document Number: 424842
Pertussis case rates in small communities of St Lucia with differing levels of vaccination coverage were compared during a pertussis epidemic in 1981. St Lucia has experienced epidemics of whooping cough at 2-5 year intervals, but no sporadic cases have been reported between cycles. By 1981, under 30% of 2 year olds on the island had received fewer than 3 DPT injections compared with 60% in 1976. The number of reported cases of whooping cough declined from 921 in 1975-76 to 470 in 1980-81. The mean age at infection in the 1981 epidemic was 4.43 years. There was a significant association between greater vaccination coverage and greater herd immunity against clinical pertussis. Vaccination coverage by health center ranged from a low of 35.2% to a high of 92.6%. The number of cases of pertussis/1000 1-3 year olds ranged from a low of zero to a high of 388 at a center where immunization coverage was 71.5%. Of the 352 cases of pertussis occurring in 1981 that involved children 1-3 years of age, 230 were from health center areas with vaccination coverage levels below 80% while only 122 cases were reported from areas with coverage rates over 80%. It is suggested that a homogeneous coverage rate of 80% of 2 year olds would eradicate pertussis from St Lucia.