In Minnesota, nearly 225,000 children born during the study period were fully vaccinated. In Oregon, there were about 180,000. In Minnesota, 458 cases of whooping cough were reported; there were 89 reported in Oregon.
The rates of whooping cough rose each year of the follow-up period. During the first year after the final vaccination, the incidence of whooping cough was 15.6 per 100,000 in the Minnesota population. By the sixth year, that rate was 138.4 per 100,000. In Oregon, a similar trend emerged, with a rate of 6.2 per 100,000 in the first year of follow-up and 24.4 per 100,000 in the last year of follow-up.
The authors said many reasons may explain why whooping cough cases are on the rise. One may be that physicians simply are more aware of the disease and may be reporting it more often. Another possible cause is the vaccine itself, they noted.
The current vaccine is an acellular vaccine, which means it doesn't contain whole cells of the bacterium responsible for pertussis infections. The previous vaccine contained whole cells of the bacterium, but was more likely to cause side effects. One of the trade-offs for reducing side effects may be a vaccine that's slightly less effective, said Dr. Kenneth Bromberg, director of the Vaccine Research Center at the Brooklyn Hospital Center in New York City.
"This study adds to the strength of argument that the acellular vaccine doesn't seem to last as long as we might have thought it would," Bromberg said.
Both experts said there are no new whooping co
All rights reserved