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Ethics of Studying Strain Replacement By Vaccinating Adults with PCV-7 in Africa

Posted by neetu on 29 Oct 2011 at 03:43 GMT

This study, although meticulously planned and well executed, raises ethical concerns.1 The PCV -7 is a vaccine for infants. When used in infancy it is known to reduce the incidence of vaccine-strain invasive pneumococcal disease in both vaccinated babies and in the non-vaccinated older population, related to reduced nasopharyngeal carriage in the vaccinated and their contacts.2, 3 Studies have also shown that vaccine-use results in strain-shifts over a period of 4 to 6 years.4 Some of the new strains that have replaced the vaccine-strains are known to be less penicillin sensitive than the strains prevalent in the community before vaccination (and so more expensive to treat).
1. In the present study PCV-7 was given in a cluster randomized trial, to adults. The vaccine is not intended for adults; and thus the experiment has been done on a group of people who are not expected to gain from it. In the words of the authors, the study vaccinating the entire population added “to the selection pressure towards an overall increase in carriage of non-vaccine type pneumococci.” The Gambia is a poor country where villagers may not easily afford antibiotics. We wonder if it was correct to subject this population to such selection pressure that could have resulted in the spread of penicillin resistant pneumococci in the community
2. We are told that community-consent from the villages was obtained and besides this, each study participant gave individualized, informed consent. We are not told what percentage of the population denied consent. We wonder if informed consent included disclosure of the study-aim to look for strain shifts and an increase in resistant bacteria in the community. The authors will be able to clarify these matters.
3. This study was limited to 2 years - instead of the 4 to 6 years required for full replacement4 and yet the authors conclude the vaccine does not increase non-vaccine strains. The authors write and we quote: “Encouragingly, vaccination of older children and adults in our study did not add selection pressure towards an overall increase in carriage of NVT pneumococci.” Such a conclusion is premature given the results of previous studies. However in view of the use of Azithromycin in the population, further study here is perhaps futile.
Neetu Vashisht and Akanksha Jain

1. Roca A, Hill PC, Townend J, Egere U, Antonio M, et al. (2011) Effects of Community-Wide Vaccination with PCV-7 on Pneumococcal Nasopharyngeal Carriage in The Gambia: A Cluster-Randomized Trial. PLoS Med 8(10): e1001107. doi:10.1371/journal.pmed.1001107

2. Lexau CA, Lynfield R, Danila R, Pilishvili T, Facklam R, et al. (2005) Changing epidemiology of invasive pneumococcal disease among older adults in the era of pediatric pneumococcal conjugate vaccine. JAMA 294: 2043–2051. doi:10.1001/jama.294.16.2043

3. Whitney CG, Farley MM, Hadler J, Harrison LH, Bennett NM, et al. (2003) Decline in invasive pneumococcal disease after the introduction of protein-polysaccharide conjugate vaccine. N Engl J Med 348: 1737–1746. doi:10.1056/NEJMoa022823.

4. Hanage WP, Finkelstein JA, Huang SS, Pelton SI, Stevenson AE, Kleinman K, Hinrichsen VL, Fraser C. Evidence that pneumococcal serotype replacement in Massachusetts following conjugate vaccination is now complete. Epidemics. 2010; 2:80-4

No competing interests declared.