The importance of supplementary immunisation activities to prevent measles outbreaks during the COVID-19 pandemic in Kenya
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Abstract
Background
The COVID-19 pandemic has disrupted routine measles immunisation and supplementary immunisation activities (SIAs) in most countries including Kenya. We assessed the risk of measles outbreaks during the pandemic in Kenya as a case study for the African Region.
Methods
Combining measles serological data, local contact patterns, and vaccination coverage into a cohort model, we predicted the age-adjusted population immunity in Kenya and estimated the probability of outbreaks when contact-reducing COVID-19 interventions are lifted. We considered various scenarios for reduced measles vaccination coverage from April 2020.
Results
In February 2020, when a scheduled SIA was postponed, population immunity was close to the herd immunity threshold and the probability of a large outbreak was 34% (8–54). As the COVID-19 contact restrictions are nearly fully eased, from December 2020, the probability of a large measles outbreak will increase to 38% (19–54), 46% (30–59), and 54% (43–64) assuming a 15%, 50%, and 100% reduction in measles vaccination coverage. By December 2021, this risk increases further to 43% (25–56), 54% (43–63), and 67% (59–72) for the same coverage scenarios respectively. However, the increased risk of a measles outbreak following the lifting of all restrictions can be overcome by conducting a SIA with ≥ 95% coverage in under-fives.
Conclusion
While contact restrictions sufficient for SAR-CoV-2 control temporarily reduce measles transmissibility and the risk of an outbreak from a measles immunity gap, this risk rises rapidly once these restrictions are lifted. Implementing delayed SIAs will be critical for prevention of measles outbreaks given the roll-back of contact restrictions in Kenya.
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SciScore for 10.1101/2020.08.25.20181198: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.Table 2: Resources
Antibodies Sentences Resources Measles immunoglobulin G (IgG) antibodies were detected using a fluorescent-bead-based multiplex immunoassay and antibody concentrations ≥0.12 IU/ml were considered protective against measles.12 For projections, we assumed these results reflected measles immunity in Kilifi in August 2019, and assumed 96% of persons >15 years had protective measles antibodies concentrations, similar to findings in adults in Nairobi in 2007-200913 (Table 1). IgGsuggested: NoneResults from OddPub: Thank you for sharing your code and data.
Results from LimitationRecognizer: We detected the following sentences addressing …SciScore for 10.1101/2020.08.25.20181198: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.Table 2: Resources
Antibodies Sentences Resources Measles immunoglobulin G (IgG) antibodies were detected using a fluorescent-bead-based multiplex immunoassay and antibody concentrations ≥0.12 IU/ml were considered protective against measles.12 For projections, we assumed these results reflected measles immunity in Kilifi in August 2019, and assumed 96% of persons >15 years had protective measles antibodies concentrations, similar to findings in adults in Nairobi in 2007-200913 (Table 1). IgGsuggested: NoneResults from OddPub: Thank you for sharing your code and data.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:Our study has a few limitations. Population immunity was only available for children <15 years but we varied observed immunity estimates in adults from a previous study in our model which resulted in a slight shift in overall immunity. The serological data, estimates and a mixing matrix used in our study may not be fully representative of the country although we utilised national estimates of vaccination coverage, which was the main driver of predicted immunity. We did not explicitly model MCV2 delivery but assumed the overall effectiveness was an average of MCV1 and MCV2 efficacy weighted by proportion of children who either receive MCV1 only or both doses. Finally, there is some uncertainty around the actual reduction in transmission due to variability in compliance with physical distancing measures in place. However, we accounted for uncertainty by varying the R0. Conclusions: Measles SIA originally scheduled for February 2020 in Kenya would have been well-timed as population immunity was below herd immunity threshold. Interruptions to RI since the start of COVID-19 pandemic restrictions in Kenya have now widened the measles immunity gap, but associated risk of large measles outbreaks are partially mitigated if COVID-19 contact restrictions remain in place. As these measures are almost fully lifted, we estimate that measles outbreak risks will dramatically increase, necessitating an immediate SIA’s to close the immunity gap.
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a protocol registration statement.
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