Dear Editor,
We are thankful to the Canadian Food Inspection Agency (CFIA) officials for drawing attention to this important topic. We fully agree with all the points that are raised by the Letter to the Editor.
However, the purpose of the paper was not to promote the use of autogenous vaccine, or to make any suggestion of their value in general. In our opinion, we don’t see how the target audience would get this impression from reading the paper. The paper dealt with the difficult issue of how to evaluate the effectiveness of vaccines in general using as an example data from one case herd with a disease outbreak in which an autogenous vaccine was being used.
From a methodological standpoint, our intention with this manuscript was to explore population-level effects of vaccination strategies in this specific herd. It is well-established that growing pigs are raised in populations with different levels of contact with other populations. As such, intervention strategies, such as immunization, may exhibit, or not, the effects that are beyond direct effects at the individual animal level. With the manuscript under consideration, our aim was to try to quantify these population and indirect effects of vaccination strategies. In this attempt, we used terminology and approaches that are based on Halloran et al (1) and related work. We recognize that there are limitations to our approach, with lack of randomization at the population level being only one of them. This is an additional reason, among others listed by the CFIA, as to why results of this study could not be extrapolated directly to other populations. However, we argue that methodologies that account for indirect and population level effects of vaccines and other interventions should be examined when it is appropriate and when it is possible in animal populations. From this perspective, we would like to emphasize, in particular, the need for continuous discussion and improvements of randomization procedures, both at the animal and at the population levels when evaluating the effectiveness of vaccines.
Footnotes
Constructive and professional comments made in the spirit of intellectual debate are welcomed by the Editor. Writers are expected to be respectful of others and to ensure that letters are considerate and courteous. The Editor reserves the right to remove comments deemed to be inflammatory or disrespectful.
Reference
- 1.Halloran ME, Longini IM, Jr, Struchiner CJ. Statistics for Biology and Health: Design and Analysis of Vaccine Studies. New York, New York: Springer; 2010. [Google Scholar]