Details of the Keyworth study

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Keyworth study

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Graph comparing cases notified per 100,000 population, Keyworth v. England and Wales

Histogram to show the ratio of Keyworth to national notifications for each year from 1977 to 2001

My published work on whooping cough includes the following most relevant papers

Outbreak of whooping cough in general practice. Jenkinson D. British Medical Journal 1978;277:896.
Synopsis of this paper
In 1977-8, 191 cases of whooping cough occurred in the Keyworth practice (11,800 patients then). This was at a time when the national immunization rate had fallen dramatically as a result of fears about the safety of the vaccine. There was general skepticism about the effectiveness of the vaccine. 126 cases were in the under fives. Because the numbers affected and unaffected were known it was possible to calculate the vaccine protection. This was 84% if those too young to be immunized were excluded. This was the first information of this sort for several decades and was soon confirmed in other studies. It was welcome news and helped with the decision to continue to recommend the vaccine as part of the national programme.

Whooping cough: what proportion of cases is notified in an epidemic? Jenkinson D. British Medical Journal 1983;287:185-6.
Synopsis of this paper
September 1982 had the greatest number of notifications in the 1982-3 epidemic in England and Wales at the time whooping cough had made a big come-back because of a low immunization rate. A postal survey asked all family doctors in Nottingham how many cases of whooping cough they had seen in September. The number (620) was compared with the number notified (116). This is 18.7%. The response rate was 83.6%. The conclusion was that even at a time of high awareness of the disease the probable real number of cases diagnosed could be at least 5 times the number notified. One might suppose that at times of low awareness, the ratio would be even higher (present times for example).

A search for subclinical infection during a small outbreak of whooping cough: implications for clinical diagnosis. Jenkinson D, Pepper JD. Journal of the Royal College of General Practitioners 1986;36:547-8. Synopsis of this paper
At the start of the 1985 outbreak in Keyworth we took pernasal swabs from all suspected cases of whooping cough and any of their contacts with any cough. 102 were taken in all. Of all these, 39 were clinically diagnosed as whooping cough and 17 of them has positive swabs. No swabs were positive in the ones without clinical whooping cough. We concluded that there was no evidence of substantial subclinical infection. We also asked about catarrhal symptoms in those with whooping cough. Only one third had catarrhal symptoms.

Duration of effectiveness of pertussis vaccine: evidence from a ten year community study. Jenkinson D. British Medical Journal 1988;296:612-4.
Synopsis of this paper
I was able to analyze the cases I had seen over 10 years in a way that permitted a calculation of the effectiveness of whooping cough vaccine at different ages. The results, based on 326 cases in the 1 to 7 year olds gave the following results. 1 year olds 100%, 2 year olds 96%, 3 year olds 89%, 5 year olds 52%, 6 year olds 54% and 7 year olds 46% protection.
Comment
Many assumptions were made for the calculation. For instance, it was assumed that the population moving in and out had suffered from whooping cough in the same way as the population in whom it had been counted. It also assumed that the number of missed cases was low, and equal in immunized and unimmunized subjects.
This paper was the subject of a paper by Connor Farrington in which he calculated the size of the possible errors. His arguments did not invalidate the result of my study. He showed the possible flaws inherent in working out vaccine effectiveness from such a simple model. In 2002 a fourth dose of pertussis vaccine was recommended in the UK in the preschool booster in order to increase immunity. This brought the UK more in line with other countries.

Natural course of 500 consecutive cases of whooping cough: a general practice population study. Jenkinson D. British Medical Journal 1995;310,299-302.'Click here to read the original paper
Synopsis of this paper
The average number of paroxysms was 13.5 per 24 hours. 11 in immunized, 15 in unimmunized.
The average duration was 52 days. 49 in immunized, 55 in unimmunized. The range was 2 to 164.
The more paroxysms, the longer the illness lasted.
The younger the patient, the longer it lasted.
57% vomited. (49% in immunized, 65% in unimmunized).
49% whooped, (39% in immunized, 56% in unimmunized).
11% had significant cessation of breathing (enough to go blue) 8% in immunized, 15% in unimmunized.
Females were affected slightly more often in childhood but twice as often in adulthood.
Females had more severe disease.
Swabs were positive in 25% of immunized, 52% of unimmunized.
5 patients developed pneumonia.