| Title:
|
The importance of supplementary immunisation activities to prevent measles outbreaks during the COVID-19 pandemic in Kenya |
| 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% (854). As the COVID-19 contact restrictions are nearly fully eased from December 2020 the probability of a large measles outbreak will increase to 38% (1954) 46% (3059) and 54% (4364) assuming a 15% 50% and 100% reduction in measles vaccination coverage. By December 2021 this risk increases further to 43% (2556) 54% (4363) and 67% (5972) 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. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12916-021-01906-9. |
| Published:
|
2021-02-03 |
| Journal:
|
BMC Med |
| DOI:
|
10.1186/s12916-021-01906-9 |
| DOI_URL:
|
http://doi.org/10.1186/s12916-021-01906-9 |
| Author Name:
|
Mburu C N |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/mburu_c_n |
| Author Name:
|
Ojal J |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/ojal_j |
| Author Name:
|
Chebet R |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/chebet_r |
| Author Name:
|
Akech D |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/akech_d |
| Author Name:
|
Karia B |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/karia_b |
| Author Name:
|
Tuju J |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/tuju_j |
| Author Name:
|
Sigilai A |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/sigilai_a |
| Author Name:
|
Abbas K |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/abbas_k |
| Author Name:
|
Jit M |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/jit_m |
| Author Name:
|
Funk S |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/funk_s |
| Author Name:
|
Smits G |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/smits_g |
| Author Name:
|
van Gageldonk P G M |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/van_gageldonk_p_g_m |
| Author Name:
|
van der Klis F R M |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/van_der_klis_f_r_m |
| Author Name:
|
Tabu C |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/tabu_c |
| Author Name:
|
Nokes D J |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/nokes_d_j |
| Author Name:
|
Scott JAG |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/scott_jag |
| Author Name:
|
Flasche S |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/flasche_s |
| Author Name:
|
Adetifa IMO |
| Author link:
|
https://covid19-data.nist.gov/pid/rest/local/author/adetifa_imo |
| sha:
|
c80433def2d88db17ad594320350d224cf6f34b9 |
| license:
|
cc-by |
| license_url:
|
https://creativecommons.org/licenses/by/4.0/ |
| source_x:
|
Medline; PMC |
| source_x_url:
|
https://www.medline.com/https://www.ncbi.nlm.nih.gov/pubmed/ |
| pubmed_id:
|
33531015 |
| pubmed_id_url:
|
https://www.ncbi.nlm.nih.gov/pubmed/33531015 |
| pmcid:
|
PMC7854026 |
| pmcid_url:
|
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7854026 |
| url:
|
https://doi.org/10.1186/s12916-021-01906-9
https://www.ncbi.nlm.nih.gov/pubmed/33531015/ |
| has_full_text:
|
TRUE |
| Keywords Extracted from Text Content:
|
roll-back
herd
SAR-CoV-2
measles
≥
COVID-19
Vaccine
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measles antibodies
measles
U5
bold lines
lockdown
Measles
RI [4] [5] [6] [7]
age-differences
participants
A. Routine
SARS-CoV-2
matrix
contacts
measles SIAs [6] [7] [8
children
measles immunoglobulin G
Nairobi in 2007-2009 [13
Kilifi
U15
Liberia
beta
Sierra Leone
upper
Kenya's devolved counties
Seventyone
MCV2 C.
MCV2
individuals
Fig. 1
Kilifi County
measles vaccine
MCV2 D.
vaccine-derived
children ≥ 9
Rubella
pre-Ebola
post-COVID-19
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fluorescent-bead-based
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measles [9
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PCVIS
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Fig. S1
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serum samples
post-lockdown
SF
FRMvdK.CNM
herd
org/10.1186/s12916-021
https://doi
measles
IMOA
DJN
GS
BK
PGMvG
Serology |
| Extracted Text Content in Record:
|
First 5000 Characters: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.
The SARS-CoV-2 pandemic has damaged the economy and disrupted social interaction and important health services in Kenya and elsewhere [1, 2] . The cumulative incidence of COVID-19 cases continues to rise in many parts of Africa suggesting the current mitigation measures will be maintained or reintroduced for periods at least until the pandemic peaks [3] .
Despite the World Health Organization (WHO) advisory to sustain routine immunisation (RI), vaccine coverage temporarily declined in many countries including Kenya that reports a 33% disruption of RI [4] [5] [6] [7] . Following guidance from the WHO, all countries suspended scheduled measles SIAs [6] [7] [8] . Measles control in Kenya is achieved by giving children a first dose of measlescontaining vaccine (MCV1) at 9 months, and a second dose (MCV2) from 18 months. SIAs, first introduced in 2002, are conducted periodically among children < 5 years or < 15 years for accelerated control of measles [9] . Based on the accumulation of susceptible children, the timing of such campaigns has typically been chosen to close immunity gaps in time to prevent potentially large measles outbreaks. A measles SIA originally planned for 2019 was rescheduled for February 2020 due to a shortfall in funding and postponed again following the COVID-19 pandemic.
Following identification of the first COVID-19 case on March 13, 2020, Kenya imposed various mitigation measures: ban on large gatherings, suspension of international flights, closure of bars, cessation of movement from hotspot counties, restriction of restaurant operating hours, and a nationwide curfew from 7 pm to 5 am. While it is plausible that these physical distancing and lock down measures may reduce the risk of measles outbreaks, they are temporary and may be associated with rebound risk periods.
The availability of recent measles serological data provided the opportunity to use Kenya as a case study to estimate the impact of reduced measles vaccination coverage and suspended SIAs due to COVID-19 on the risk of measles outbreaks.
This study used a cohort mathematical model that combined measles serological data, local contact patterns, and vaccination coverage estimates.
We estimated measles immunity profile in children using serum samples collected during serological surveys among residents of Kilifi Health and Demographic Surveillance System (KHDSS) Kilifi, Kenya [10] for the Pneumococcal Conjugate Vaccine Impact Study (PCVIS) [11] . These serosurveys, conducted every 2 years since 2009, target 50 KHDSS randomly selected children in ten age strata (0, 1, 2, 3, 4, 5, 6, 7, (8) (9) , and 10-14 years) and blood samples < 2 ml were collected from participants. The sample size for the PCVIS serosurveys was calculated to obtain narrow confidence intervals around the estimate of prevalence of immune response both overall and by age-category for each serosurvey year. For instance, for a proportion of 0.80, the 95% confidence intervals (CIs) would be 0.77-0.84 overall and 0.69-0.91 in each age stratum.
In the 2019 serosurvey, there were 497 participants and the blood samples were collected in July (165), August (162), September (130), and October (40). We tested for measles immunoglobulin G (IgG) antibodies using a |
| Keywords Extracted from PMC Text:
|
pre-COVID-19
measles SIAs
MCV2C.Routine
MCV2D.Routine
Fig. S1
matrix
individuals
pre-Ebola
persons
under-fours
Nairobi in
19–54
measles [9
Kilifi County
vaccine-derived
measles immunoglobulin G
herd
serum samples
measles antibodies
81–87
MCV2 vaccine
measles
A.Routine
PCVIS
Kilifi
age-differences
Sierra Leone
blood samples
−
Rubella
measles [12]
IgG
measles vaccine
40–64
Measles
participants
43–63
samples
43–64
children ≥ 9
8–9
CIs
≥
sameB.Routine
upper
85–91
COVID-19 contact restrictions
MCV1-eligible children
post-COVID-19
COVID-19
lockdown
Kilifi [18
82–94
's
Liberia
MCV2
children
SARS-CoV-2
Fig. 1
measles-containing vaccine
fluorescent-bead-based
85–92
infants |
| Extracted PMC Text Content in Record:
|
First 5000 Characters:The SARS-CoV-2 pandemic has damaged the economy and disrupted social interaction and important health services in Kenya and elsewhere [1, 2]. The cumulative incidence of COVID-19 cases continues to rise in many parts of Africa suggesting the current mitigation measures will be maintained or reintroduced for periods at least until the pandemic peaks [3].
Despite the World Health Organization (WHO) advisory to sustain routine immunisation (RI), vaccine coverage temporarily declined in many countries including Kenya that reports a 33% disruption of RI [4–7]. Following guidance from the WHO, all countries suspended scheduled measles SIAs [6–8]. Measles control in Kenya is achieved by giving children a first dose of measles-containing vaccine (MCV1) at 9 months, and a second dose (MCV2) from 18 months. SIAs, first introduced in 2002, are conducted periodically among children < 5 years or < 15 years for accelerated control of measles [9]. Based on the accumulation of susceptible children, the timing of such campaigns has typically been chosen to close immunity gaps in time to prevent potentially large measles outbreaks. A measles SIA originally planned for 2019 was rescheduled for February 2020 due to a shortfall in funding and postponed again following the COVID-19 pandemic.
Following identification of the first COVID-19 case on March 13, 2020, Kenya imposed various mitigation measures: ban on large gatherings, suspension of international flights, closure of bars, cessation of movement from hotspot counties, restriction of restaurant operating hours, and a nationwide curfew from 7 pm to 5 am. While it is plausible that these physical distancing and lock down measures may reduce the risk of measles outbreaks, they are temporary and may be associated with rebound risk periods.
The availability of recent measles serological data provided the opportunity to use Kenya as a case study to estimate the impact of reduced measles vaccination coverage and suspended SIAs due to COVID-19 on the risk of measles outbreaks.
We estimated measles immunity profile in children using serum samples collected during serological surveys among residents of Kilifi Health and Demographic Surveillance System (KHDSS) Kilifi, Kenya [10] for the Pneumococcal Conjugate Vaccine Impact Study (PCVIS) [11]. These serosurveys, conducted every 2 years since 2009, target 50 KHDSS randomly selected children in ten age strata (0, 1, 2, 3, 4, 5, 6, 7, 8–9, and 10–14 years) and blood samples < 2 ml were collected from participants. The sample size for the PCVIS serosurveys was calculated to obtain narrow confidence intervals around the estimate of prevalence of immune response both overall and by age-category for each serosurvey year. For instance, for a proportion of 0.80, the 95% confidence intervals (CIs) would be 0.77–0.84 overall and 0.69–0.91 in each age stratum.
In the 2019 serosurvey, there were 497 participants and the blood samples were collected in July (165), August (162), September (130), and October (40). We tested for measles immunoglobulin G (IgG) antibodies using a fluorescent-bead-based multiplex immunoassay. Antibody concentrations ≥ 0.12 IU/ml were considered protective against measles [12].
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 2007–2009 [13] (Table 1). We also assumed protection from maternal immunity was similar to the proportions of the infants < 9 months old who had protective antibodies.
MCV1 national coverage in Kenya has been between 75 and 80% since its introduction in 1985 [17]. MCV2 was introduced in Kenya in 2013 and coverage rose up to 45% in 2018 [9]. The last measles SIA in children aged 9 months to 14 years took place in 2016 and achieved 95% coverage [22].
We assumed national MCV1 and MCV2 coverage were 79% and 45%, respectively, in 2018, and that these stayed at the same level from August 2019 until the end of March 2020 when COVID-19 contact restrictions were introduced in Kenya. From April 2020, we explored the following routine vaccination coverage scenarios alongside a suspended SIA.
A.Routine vaccination coverage remained the sameB.Routine vaccination coverage reduced by 15% for both MCV1 and MCV2C.Routine vaccination coverage reduced by 50% for both MCV1 and MCV2D.Routine vaccination was suspended
We used an age-mixing matrix which consisted of the number of contacts between six different age groups. The matrix was generated from diary studies conducted in Kilifi, Kenya [21], using a bootstrap of 4000 samples by randomly sampling n individuals with replacement from the n participants of the contact survey.
We adapted a static cohort model of measles immunity [23] to estimate age-stratified population immunity profile in Kilifi by combining recent measles serological data with new vaccine-derived immunity during the prediction period using the |
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