Decreasing Antibody Titers and the Slow Decay of Measles Immunity in Mexico’s Current Epidemiological Landscape

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

The manuscript titled‌“Waning Antibody Titers and the Silent Decay of Measles Immunity in Mexico's Current Epidemiological Landscape”addresses a timely and important topic regarding the "silent decay" of measles immunity in the Mexican adult population. The cross-sectional design provides valuable sero-epidemiological data. However, the interpretation of statistical results, particularly the relationship between age and antibody titers, requires refinement to avoid logical inconsistencies. Additionally, the manuscript would benefit from improved language editing.

1. Unclear Primary Objective:‌ The Aim stated in the Abstract ("To estimate the seroprevalence... and to identify... determinants") does not align perfectly with the stronger conclusion drawn about "silent erosion of immunity." Consider reframing the primary objective to focus more explicitly on ‌evaluating evidence for waning vaccine-induced immunity in younger cohorts‌.

 

2. Sample Representativeness:‌ A critical limitation is the use of ‌voluntary blood donors‌. This cohort is not representative of the general Mexican adult population in terms of health status and potentially healthcare access. This severely limits the generalizability of the seroprevalence estimate (67.2%). This must be stated as a ‌primary limitation‌ in the Discussion.

3.Seroprotection Threshold:‌ The manuscript uses the kit's positive threshold (>200 mIU/mL). It should be clearly stated that this is a ‌manufacturer's recommended level for indicating past exposure/vaccination‌ and may not correspond directly to a ‌correlate of protection against infection‌, which is a more complex immunological concept.

4.The results indicate a positive correlation between age and antibody titers; however, this is based on a cross-sectional study. In the discussion, you referred to “waning antibody levels over time,” yet the data show higher antibody levels in older individuals. It is important to clarify the logic: you are comparing different cohorts (cohort effect) rather than tracking changes within the same individuals over time. Avoid using “waning” to describe the data from older individuals—this term is more appropriate for describing the decline observed in younger cohorts over time.

5.When reporting Geometric Mean Titers (GMTs), such as in Table 1 and Figure 3, it is recommended to show the 95% confidence intervals (CIs) in addition to the P-values.

Author Response

Comment 1:

The manuscript titled “Waning Antibody Titers and the Silent Decay of Measles Immunity in Mexico's Current Epidemiological Landscape” addresses a timely and important topic regarding the "silent decay" of measles immunity in the Mexican adult population. The cross-sectional design provides valuable sero-epidemiological data. However, the interpretation of statistical results, particularly the relationship between age and antibody titers, requires refinement to avoid logical inconsistencies. Additionally, the manuscript would benefit from improved language editing.

Answer 1: We thank the reviewer for this valuable comment. We have refined the interpretation of the association between age and anti-measles IgG levels to clarify that the observed correlation in unadjusted analyses reflects cohort-specific differences rather than a biological effect of aging per se. This clarification has been incorporated into the Results and Discussion sections.

In addition, the manuscript has undergone comprehensive language editing to improve clarity, consistency and academic tone throughout.

Comment 2:

Unclear Primary Objective:‌ The Aim stated in the Abstract ("To estimate the seroprevalence... and to identify... determinants") does not align perfectly with the stronger conclusion drawn about "silent erosion of immunity." Consider reframing the primary objective to focus more explicitly on ‌evaluating evidence for waning vaccine-induced immunity in younger cohorts‌.

Answer 2: We appreciate this insightful comment. The study objective has been refined to align more clearly with the main findings, emphasizing the evaluation of age- and cohort-specific patterns of measles antibody levels and evidence consistent with diminished vaccine-induced immunity in younger vaccinated cohorts. The conclusion was also revised to ensure consistency with the stated aim and the cross-sectional design.

Comment 3:

Sample Representativeness: A critical limitation is the use of  voluntary blood donors‌. This cohort is not representative of the general Mexican adult population in terms of health status and potentially healthcare access. This severely limits the generalizability of the seroprevalence estimate (67.2%). This must be stated as a ‌primary limitation‌ in the Discussion.

Answer 3: We agree with the reviewer.  The limitation regarding the use of voluntary blood donors and its implications for generalizability has been strengthened and clearly emphasized in the Discussion section. We explicitly state that the seroprevalence estimate should not be interpreted as nationally representative of the Mexican adult population.

Comment 4:

3. Seroprotection Threshold:‌ The manuscript uses the kit's positive threshold (>200 mIU/mL). It should be clearly stated that this is a ‌manufacturer's recommended level for indicating past exposure/vaccination‌ and may not correspond directly to a ‌correlate of protection against infection‌, which is a more complex immunological concept.

Answer 4: We thank the reviewer for this important clarification. The Methods section has been revised to specify that the >200 mIU/mL threshold corresponds to the manufacturer’s recommended cut-off for indicating prior exposure or vaccination and does not represent an absolute correlate of protection. Additionally, the Discussion section now emphasizes that protective immunity against measles involves neutralizing capacity, antibody avidity, and cellular immune responses, which were not assessed in this study.

 

Comment 5:

4.The results indicate a positive correlation between age and antibody titers; however, this is based on a cross-sectional study. In the discussion, you referred to “waning antibody levels over time,” yet the data show higher antibody levels in older individuals. It is important to clarify the logic: you are comparing different cohorts (cohort effect) rather than tracking changes within the same individuals over time. Avoid using “waning” to describe the data from older individuals—this term is more appropriate for describing the decline observed in younger cohorts over time.

Answer 5: We agree with the reviewer’s observation. Given the cross-sectional design, our data reflect cohort-specific differences rather than intra-individual longitudinal decline. The Discussion has been revised to clarify that the observed pattern represents a cohort effect and that the term “waning immunity” is used cautiously to describe reduced antibody levels in younger vaccinated cohorts rather than decline within individuals over time.

Comment 6:

5.When reporting Geometric Mean Titers (GMTs), such as in Table 1 and Figure 3, it is recommended to show the 95% confidence intervals (CIs) in addition to the P-values.

Answer 6: We appreciate this recommendation. Geometric mean concentrations (GMCs) are now reported with their corresponding 95% confidence intervals in tables and figures to improve the precision and interpretability of the results.

We thank the reviewer for the constructive comments, which have significantly improved the clarity, rigor, and interpretability of the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

This is a plain description of results of measles virus serology in adult blood donors from Mexico.

The study does not involve high tech, but a commercial immunoenzyme assay of IgG levels against measles virus. The design combines serology with structured interviews of participants on past measles vaccination and/or natural measles infection.

Adding additional data could increase the interest of readers and the quality of MS. For instance: 1) total IgG measurements; 2) measles neutralizing Ab titers; 3) comparison of current results with those of studies form other continents or nations; 4) other.

Figures need to be improved (enhancing contrast: for instance, symbols in black + SD intervals represented with transparent light grey/color).

References can be improved by adding 1) general references on measles virus receptors and selectivity for humans, 2) infection of non-human primates and lack of evidence for virus transmission among animals in the wild, 3) measles serology results of studies of sizeable (>200) populations in the Americas, Europe, other nations. These latter data need to be compared to results from Mexico in the Discussion section.

Observations:

Title: silent decay (probably better slow decay).

Line 45 etc.: please add the receptor molecules measles virus is using in human cells. In addition, please report on the possible infection of non-human primates and why infection is held not to be spreading in the wild (Ref. needed).

57: an estimated 136,200 deaths... How has this been estimated, with what evidence degree? This is not adequately explained in Ref. 7.

63: explain in more detail why it is held that there are no sources other than humans that justify the possible eradication of measles (add Ref.).

74: underscoring the need to analyze the duration of both humoral and cell-mediated immunity against measles (add Ref.).

146: the largest proportion of... probably better: 31.5% participants.

Table 1: History of measles vaccination, n (%) – please list as follows: Vaccinated, number of doses unknown; 1 dose; 2 doses; 3 doses; Unknown.

265: elimination. Measles has not been eliminated in Mexico or other countries. Measles incidence has been reduced through vaccination.

307-308: measles vaccination in childhood remains a partially effective strategy...

Author Response

This is a plain description of results of measles virus serology in adult blood donors from Mexico.

The study does not involve high tech, but a commercial immunoenzyme assay of IgG levels against measles virus. The design combines serology with structured interviews of participants on past measles vaccination and/or natural measles infection.

Comment 1:

Adding additional data could increase the interest of readers and the quality of MS. For instance: 1) total IgG measurements; 2) measles neutralizing Ab titers; 3) comparison of current results with those of studies form other continents or nations; 4) other.

Answer 1: We thank the reviewer for these valuable suggestions. We agree that total IgG measurements and neutralizing antibody titers (e.g., PRNT) would provide a more comprehensive assessment of functional immunity. However, the present study was designed as a seroepidemiological survey using a standardized commercial ELISA platform to ensure comparability with other population-based studies. Functional assays and total IgG measurements were beyond the scope of this investigation.

To address the reviewer’s suggestion regarding broader comparisons, we have expanded the Discussion to include additional comparisons with seroepidemiological studies from Europe, Latin America, Asia, and North Amerca, thereby enhancing the international relevance and contextualization of our findings.

Comment 2:

Figures need to be improved (enhancing contrast: for instance, symbols in black + SD intervals represented with transparent light grey/color).

Answer 2: We appreciate this recommendation. All figures have been reformatted to improve clarity and interpretability, including enhanced contrast, consistent symbol formatting, and clearer representation of variability measures.

Comment 3:

References can be improved by adding 1) general references on measles virus receptors and selectivity for humans, 2) infection of non-human primates and lack of evidence for virus transmission among animals in the wild, 3) measles serology results of studies of sizeable (>200) populations in the Americas, Europe, other nations. These latter data need to be compared to results from Mexico in the Discussion section.

Answer 3: We thank the reviewer for this helpful suggestion. The Introduction has been expanded to include key references on measles virus host selectivity, receptor usage, and the absence of sustained transmission in non-human animal populations. These additions strengthen the biological rationale for measles elimination. Additionally, the Discussion now incorporates comparisons with large seroepidemiological studies from multiple regions, highlighting similarities between our findings and global patterns of cohort-specific differences in measles immunity.

Comment 4:

Title: silent decay (probably better slow decay).

Answer 4: We appreciate this suggestion. The title has been revised to improve clarity and scientific tone by replacing “silent decay” with terminology that more accurately reflects the observed cohort-related decline in antibody levels.

Comment 5:

Line 45 etc.: please add the receptor molecules measles virus is using in human cells. In addition, please report on the possible infection of non-human primates and why infection is held not to be spreading in the wild (Ref. needed).

Answer 5: We thank the reviewer for this important suggestion. This information has been updated in the revised version.

Comment 9:

57: an estimated 136,200 deaths... How has this been estimated, with what evidence degree? This is not adequately explained in Ref. 7.

Answer 9: We appreciate this reviewer's observation. The description of measles mortality estimates has been clarified by citing updated WHO/UNICEF and CDC modeling approaches, which use national immunization coverage data and surveillance reports to generate annual estimates of measles cases and deaths.

Comment 10:

63: explain in more detail why it is held that there are no sources other than humans that justify the possible eradication of measles (add Ref.).

Answer 10: We thank the reviewer for this suggestion. The Introduction now clarifies that humans are considered the sole natural reservoir of measles virus because sustained transmission has not been documented in animal populations, despite occasional infections in non-human primates. This characteristic supports the feasibility of measles eradication.

Comment 11:

74: underscoring the need to analyze the duration of both humoral and cell-mediated immunity against measles (add Ref.).

Answer 11: We appreciate this recommendation. Additional references have been incorporated to support the discussion on the duration of humoral and cell-mediated immunity following measles vaccination and natural infection.

Comment 12:

146: the largest proportion of... probably better: 31.5% participants.

Answer 12: We thank the reviewer for this clarification. The text has been revised to report the proportion explicitly as 31.5% of participants.

Comment 13:

Table 1: History of measles vaccination, n (%) – please list as follows: Vaccinated, number of doses unknown; 1 dose; 2 doses; 3 doses; Unknown.

Answer 13: We appreciate the reviewer’s suggestion. Table 1 has been reformatted to present vaccination history categories in the requested order and format.

Comment 14:

265: elimination. Measles has not been eliminated in Mexico or other countries. Measles incidence has been reduced through vaccination.

Answer 14: We thank the reviewer for this important clarification. The text has been revised to avoid implying complete elimination and instead refers to reduced incidence and interruption of endemic transmission.

Comment 15:

307-308: measles vaccination in childhood remains a partially effective strategy...

Answer 15: We appreciate this comment. The statement has been revised to better reflect the high effectiveness of measles vaccination while acknowledging the potential for waning immunity and susceptibility gaps.

We thank the reviewer for the insightful comments, which have strengthened the biological context, international relevance, and clarity of the manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All concerns have been adequately addressed and resolved

Author Response

The authors appreciate the reviewer's thorough review of this manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The MS has improved in the Introduction and Discussion sections, including References.

Results remained the same, with improved Figures.

Authors did not provide some of the requested additional data.

One possible addition to the Discussion: Is there a concomitant decrease of Ab titers to rubella and mumps in young adults who were immunized with MMR? That would be useful to add and comment (lines 353-357).

Author Response

The MS has improved in the Introduction and Discussion sections, including References.

Results remained the same, with improved Figures.

Authors did not provide some of the requested additional data.

Question: One possible addition to the Discussion: Is there a concomitant decrease of Ab titers to rubella and mumps in young adults who were immunized with MMR? That would be useful to add and comment (lines 353-357).

Response 1: We appreciate this valuable observation. We agree that acknowledging the concomitant waning of immunity against rubella and mumps provides important context for the MMR-vaccinated cohorts. We have updated the Discussion accordingly to briefly address this phenomenon (lines 350-355).

The authors appreciate the reviewer's thorough review of this manuscript.