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Influenza Vaccination in Children with Asthma

No Reason to Change Current Recommendations

We fully agree with Fleming and Monto that our findings (1) should not be misinterpreted: there may indeed be influenza seasons in which vaccination of children with asthma is more effective than it was in the two seasons that we studied.

The primary endpoint of the study was indeed exacerbations. However, also for upper and lower respiratory tract symptoms, no differences were found between vaccine and placebo.

The issue of our power calculation has been raised before. We doubt whether the projected incidence rates for influenza were really too high, considering the serologic changes in the placebo group. Now that the study has finished, power is not an issue anymore. We quote Altman and colleagues: "There is ... little merit in calculating the statistical power once the results of the trial are known; the power is then appropriately indicated by confidence intervals" (2).

As to the reported mildness of the season 2000–2001, we stress that this was not the case for children, as reported in the Dutch influenza bulletin (3).

The proportion of children participating in our study that had been vaccinated before was 55% (ever-vaccinated) and 52% (previous season). With regard to severity, we point out that about 90% of children used maintenance medication. Our impression is that participating children were a reasonable reflection of the children with moderate and more severe asthma in general practice.

Should we have provided results separately for each of the two seasons? We decided against this, as in our protocol we set out to combine the seasons and the planned sample size was too small to give precise estimates per season. Moreover, clinical effectiveness of influenza vaccination per se in everyday practice has to take into account more and different seasons.

We entirely agree that studies of this nature should also include virology for respiratory syncytial virus. We have published these outcomes for our study, including other viruses as well, in a subsequent article (4).

Taking the point estimates of our study, in the first season it would have been necessary for 30 children to have been vaccinated to prevent one influenza-induced exacerbation. In the second season it was better not to have been vaccinated. We look forward to future studies contributing to this issue. Perhaps it would then be possible to combine results to provide a pooled average for the number of children that would have to be vaccinated to prevent one exacerbation. With this information children, parents, and doctors could then make their own evidence-based choice.

Herman J. Bueving, Siep Thomas and Johannes C. van der Wouden

Erasmus MC—University Medical Center Rotterdam Rotterdam, The Netherlands

FOOTNOTES

Conflict of Interest Statement: H.J.B. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript; S.T. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript; J.C.v.d.W. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Bueving HJ, Bernsen RMD, de Jongste JC, van Suijlekom-Smit LWA, Rimmelzwaan GF, Terhaus ADME, Rutten-van Mölken MPMH, Thomas S, van der Wouden JC. Influenza vaccination in children with asthma: randomized double-blind placebo-controlled trial. Am J Respir Crit Care Med 2004;169:488–493.[Abstract/Free Full Text]
2. Altman DG, Moher D, Schulz KF. Peer review of statistics in medical research: reporting power calculations is important. BMJ 2002;325:491.[Free Full Text]
3. Nieuwsbrief influenza-surveillance 2000/01;9(Pt 5) [in Dutch].
4. Bueving HJ, van der Wouden JC, Raat H, Bernsen RMD, de Jongste JC, van Suijlekom-Smit LWA, Osterhaus ADME, Rimmelzwaan GF. Rutten- van Mölken MPMH, Thomas S. Influenza vaccination in asthmatic children: effects on quality of life and symptoms. Eur Resp J. 2004;24:925–931.[Abstract/Free Full Text]

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