such as "Introduction", "Conclusion"..etc
Immunity to whooping cough lasts at least 30 years on average, much
longer than previously thought, according to a new study by researchers
based at the University of Michigan and the University of New Mexico.
Details are published October 30 in the open-access journal PLoS
Once thought to be under control following widespread childhood
vaccination, whooping cough (pertussis) has been on the rise since the
1980s in the United States and several other countries. Several
explanations have been proposed for the surprising increase in cases,
and one leading idea is that the immunity enjoyed by vaccinated or
previously exposed people is waning. It has been documented that, in
some individuals, immunity has waned over time, but details of how long
protection typically lasts and how its waning affects disease
transmission have not been clear.
To try to answer these questions, Pejman Rohani (based at the
University of Georgia during completion of this study) and Helen Wearing
used mathematical models to explore various scenarios and compared the
predictions generated by those models to data on whooping cough
The researchers constructed two different models based on assumptions
of the effects of pertussis exposure on a person whose immunity has
lapsed and that person's relative contribution to transmission. Then
they compared the models' predictions to whooping cough incidence data
from England and Wales from both the pre-vaccine era (1945-1957) and the
vaccine era (1958-1972).
In particular, Rohani and Wearing looked for matches in two key
measures: the number of years between big outbreaks and the frequency of
"extinctions"---periods of time when no whooping cough cases were
reported in the population. The analysis revealed that, on average,
whooping cough immunity lasts at least 30 years and perhaps as long as
70 years after natural infection.
"This is surprising because clinical epidemiologists currently
believe the duration of pertussis immunity is somewhere between four and
20 years," said Rohani.
In addition, repeat infections appear to contribute relatively little
to the transmission cycle, the researchers found. And when people whose
immunity has waned are re-exposed to whooping cough, they rarely become
infected. In fact, their immunity to the disease may be boosted by
re-exposure, the study suggests. Still, the researchers are cautious
about drawing conclusions about current day vaccination practices from
their study of historical data.
"It's worth pointing out that in the past 20 years or so, the nature
of the vaccines that have been used has changed quite fundamentally,"
Rohani said. The data we're using are from a time when a whole-cell
vaccine was in use; now an acellular vaccine, which stimulates a
different part of the immune system, is typically used, especially in
In response, Rohani is doing new work using more recent data from the
U.S., such as birth rates, population size, and vaccination coverage,
to uncover relevant factors associated with trends in whooping cough
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