Title: Childhood vaccination in informal urban settlements in Nairobi, Kenya: Who gets vaccinated?

Transcription

1 Author's response to reviews Title: Childhood vaccination in informal urban settlements in Nairobi, Kenya: Who gets vaccinated? Authors: Martin K Mutua (mkavao@aphrc.org) Elizabeth Kimani (ekimani@aphrc.org) Remare Ettarh (rettarh@aphrc.org) Version: 2 Date: 14 October 2010 Author's response to reviews: see over

2 Title: Childhood vaccination in informal urban settlements in Nairobi, Kenya: Who gets vaccinated? Response to reviewers comments Reviewer s comments Reviewer # 1: James Ndirangu Discretionary revisions 1. Would be useful for the reader to know the number of public health facilities, providing vaccination services, in the setting. Minor Essential Revisions 1. How does the proportion of children with vaccination cards seen during the interview compare with the proportions in the province as per the Kenya DHS referred in the background? Is this figure lower or higher? 2. Another possible explanation of children in Viwandani slum being more likely to be fully vaccinated (in bivariate analysis) may be because this area attracts migrant workers with relatively higher education levels. Higher maternal (or paternal) education level may positively influence the likelihood of full vaccination. 3. From the authors experience of the setting, what reasons would explain why OPV0 had much lower coverage than BCG though they are both given at the time of birth of the child? 4. The low immunization coverage for measles in this study is also of concern because of herd immunity thus the whole population of children would be at high risk in case of measles outbreak. Major Compulsory Revisions 1. There are 140 children who though included in the bivariate analysis (Table 3) are excluded from the multivariate analysis (Table 4) i.e. N in bivariate analysis is 1,846 while that in multivariate is 1,706. No explanation for this discrepancy is addressed in the paper. Response This has been indicated (See Methods Section, Paragraph 1, page 4) This has been indicated. section, last paragraph page 9). This explanation has been added. section, page 9 paragraph 1) section, page 8, paragraph 3) This concern has been section, page 8, paragraph 2) The reasons have been included (See Multivariate results section, page 6)

3 2. As with the national DHS, when vaccination cards were not seen at the time of interview, the mother is asked to recall if the child had received any of the vaccinations. Maternal reports of vaccination status have been validated and observed to be an accurate source of children s vaccination status. Further, reliance on vaccination card only may represent a lower bound of vaccination coverage (see Langsten R, Hill K: The accuracy of mothers' reports of child vaccination: evidence from rural Egypt. Social Science and Medicine 1998, 46(9): ). Therefore, if the authors have access maternal recall information, on the 12% Whose vaccination cards were not seen and thus omitted from the analysis, they can do a sensitivity analysis on how such information would affect the results presented. 3. The authors do not discuss whether there were any significant differences Between the children whose vaccination cards were seen (n=124) and not seen (n=1846) at the time of the interview. Though only a relatively small proportion (12%) did not have vaccination cards, this could affect vaccination coverage, for instance, if a large part of these were immunized with measles vaccine which has the lowest coverage. 4. The authors did not refer to any statistical tests conducted on their final models. For instance, model selection criterions considering goodness-of-fit measures e.g. AIC or BIC would be flexibly used. Table 2 has been modified to show coverage when mother recall details are Table 2 has been modified to show coverage when mother recall details are AIC values have been added to all fitted models (See Table 5)

4 Reviewer #2: Peter Aaby General comments 1. Measles vaccine has consistently been found to be the most life-saving of all the routine vaccines. Hence, the main observation in this study is the total disparity in the coverage for measles vaccine on one side and BCG/DTP/OPV on the other side. This could deserve a bit more emphasis in both results and discussion. I would suggest that the authors also made a risk factor analysis for not being measles vaccinated. The diagnosis of the problem of missing measles vaccination may be better than through getting mixed with other vaccines in the concept fully vaccinated by 12 months. 2. There is also a disparity in the coverage for OPV3 and DTP3 (13%) which does not seem to be there for the first and second doses. Any explanation for this? A temporary shortage? but that would presumably have affected all the OPV doses. Since the donors are using DTP3 to monitor the performance of the vaccination programme one might expect the programmes putting more emphasis on DTP3. Is this part of the explanation and how does it work? 3. The discussion raises several issues which might benefit from a little more analysis/commenting: i. It is mentioned that the OPV-0 coverage is much lower than BCG. Why is that? When a visited a few health centres in (rural) Kenya I was told that OPV0 was only given until 14 days after delivery. It should be possible to see from the data sets whether there is any specific timing in who is not getting OPV-0 with BCG. ii. Why the coverage for OPV3 13% lower than for DTP3 (page 8)? Minor comments Abstract 1. Methods: The second last sentence is unclear with respect to how these visits relate to the age group months. 2. Results. A distinction is made between Full coverage and up-to-date coverage but these concepts are not explained. If used in the abstract they need to be explained. The point is well noted and very relevant. However, the objective of the study was not focussing on measles but a study of full vaccination in the slums. Subsequent analysis is underway to examine coverage and timing issues around specific vaccinations and measles is a priority in this. section, page 8, paragraph 3) Details on timing to BCG and OPV-0 vaccinations have in Table 3. Results section (page 6, parag. 2)and Discussion (page 9, parag. 1) have also been revised to include the new results. (See discussion section, page 8, paragraph 3) (file attached) Sentence has been revised (See page 2, parag. 2) This part of the abstract has been revised accordingly (See Page 2)

5 3. Page 4: The vaccination details were collected during first visit with updates repeated during the first and second quarterly follow-up visits. This sentence is unclear with how it relates to the age group months. Is it the first visit after 12 months? then say so. One is left wondering whether vaccination details were not collected during the first year of life. 4. UTD=up-to-date vaccinations. The description is unclear as to whether UTD is just all recommended vaccinations before 12 months or age or whether the vaccines should have been received in the recommended sequence. I assumed the first but the description should be clear. However, this is further complicated by the later use of the concept of UTD at 3 months of age (Table 2 and discussion). In the discussion it is said: This study indicates a lower level of up-to-date vaccination than that of full coverage, declining from 66% for vaccinations that should be completed by 3 months including BCG, polio 1, 2, 3 and DTP/pentavalent 1, 2, 3 to 52% at 12 months when all vaccines should have been given. However, the 3rd dose of DTP and OPV is supposed to be given at 14 weeks which is after 3 months of age. Strictly speaking UTD at 3 months would only imply having received BCG and 2 doses of OPV and DTP. Hence, a clarification is needed as to what age has been used to measure the UTP at 3 months. 5. Page 5: What is village level in the slums? Districts in the slums or village of origin? 6. Tables 3 and 4 It would be more informative to have the OR estimates with confidence intervals than just to have * for the level of significance Discussion 7. Page 8-9. Kikuyu has apparently been noted before to have higher vaccination coverage. Any explanation for that? Has services been better developed in Kikuyu areas, socio-economic or schooling conditions, or other cultural factors. The strongest differences in the study are the one between the two slum areas and the one between the ethnic groups. A bit more explanation/speculation of possible causes would be good. This part of the abstract has been revised accordingly (See Page 4, parag. 2 & 3) The clarification of the meaning of UTD is this study has. (See Page 4, parag. 2 & 3) Correction of the error in discussion has been effected. section, page 8, paragraph 2) This has been modified (Page 4, parag. 1 & 4) Confidence Intervals have been added in all models (Tables 4, 5) This explanation has been added. section, page 9 paragraph 1) This explanation has been added. section, page 9 paragraph 1)