Letter

Non-specific effects of vaccination

BMJ 2005; 330 doi: 10.1136/bmj.330.7495.844-b (Published 7 April 2005)
Cite this as: BMJ 2005;330:844.3

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Survival bias may explain findings

  1. Peter Aaby, professor (psb@mail.gtelecom.gw),
  2. Henrik Jensen, senior statistician,
  3. Christine Stabell Benn, senior researcher,
  4. Ida Maria Lisse, registrar
  1. Bandim Health Project, Danish Epidemiology Science Centre, Statens Serum Institute, Apartado 861, Bissau, Guinea-Bissau

    EDITOR—Vaugelade et al found the BCG and diphtheria-tetanus and pertussis vaccines (DTP) to be associated with reductions in mortality greater than expected from disease prevention.1 However, as they admit, dead vaccinated children may have been misclassified because their vaccination cards were destroyed.

    In a survival analysis using vaccination dates as time dependent covariates, surviving children change status at date of vaccination even though vaccinations …

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