Challenges Addressing Inequalities in Measles Vaccine Coverage in Zambia through a Measles–Rubella Supplementary Immunization Activity during the COVID-19 Pandemic

Abstract

Background: Measles–rubella supplementary immunization activities (MR-SIAs) are conducted to address inequalities in coverage and fill population immunity gaps when routine immunization services fail to reach all children with two doses of a measles-containing vaccine (MCV). We used data from a post-campaign coverage survey in Zambia to measure the proportion of measles zero-dose and under-immunized children who were reached by the 2020 MR-SIA and identified reasons associated with persistent inequalities following the MR-SIA. Methods: Children between 9 and 59 months were enrolled in a nationally representative, cross-sectional, multistage stratified cluster survey in October 2021 to estimate vaccination coverage during the November 2020 MR-SIA. Vaccination status was determined by immunization card or through caregivers’ recall. MR-SIA coverage and the proportion of measles zero-dose and under-immunized children reached by MR-SIA were estimated. Log-binomial models were used to assess risk factors for missing the MR-SIA dose. Results: Overall, 4640 children were enrolled in the nationwide coverage survey. Only 68.6% (95% CI: 66.7%, 70.6%) received MCV during the MR-SIA. The MR-SIA provided MCV1 to 4.2% (95% CI: 0.9%, 4.6%) and MCV2 to 6.3% (95% CI: 5.6%, 7.1%) of enrolled children, but 58.1% (95% CI: 59.8%, 62.8%) of children receiving the MR-SIA dose had received at least two prior MCV doses. Furthermore, 27.8% of measles zero-dose children were vaccinated through the MR-SIA. The MR-SIA reduced the proportion of measles zero-dose children from 15.1% (95% CI: 13.6%, 16.7%) to 10.9% (95% CI: 9.7%, 12.3%). Zero-dose and under-immunized children were more likely to miss MR-SIA doses (prevalence ratio (PR): 2.81; 95% CI: 1.80, 4.41 and 2.22; 95% CI: 1.21 and 4.07) compared to fully vaccinated children. Conclusions: The MR-SIA reached more under-immunized children with MCV2 than measles zero-dose children with MCV1. However, improvement is needed to reach the remaining measles zero-dose children after SIA. One possible solution to address the inequalities in vaccination is to transition from nationwide non-selective SIAs to more targeted and selective strategies.

High measles and rubella vaccine coverage and seroprevalence among Zambian children participating in a measles and rubella supplementary immunization activity

“…This flags the need to develop strategies to target larger families. These inequities in vaccination status were also identified at the national level [14].…”

“…Further, as we only enrolled a relatively small sample of the children attending the campaign, it is also possible that the study children do not fully represent all children who attended the SIA in these districts. Finally, this study was nested in a vaccination campaign that occurred during the COVID-19 pandemic and had lower coverage compared to previous SIAs, which could impact who was included in our study [14]. However, we expect that the potential bias is relatively small in terms of who was missed from the SIA.…”

“…The Zambian Ministry of Health also has a long history of successful SIAs, reaching over 3 million children with MR vaccines during Child Health Week in November 2020 [12]. However, measles outbreaks subsequently were reported in several districts in 2022 and 2023, possibly due to lower than optimal coverage of the November 2020 MR vaccination campaign and disruptions to the routine immunization program in 2020-2021 due to the COVID-19 pandemic [13, 14]. Since the impact of SIAs on population immunity cannot be adequately determined by vaccination coverage estimates alone, we conducted a MR serosurvey nested within the SIA to estimate the proportion of susceptible children vaccinated during the November 2020 MR SIA in Zambia.…”

Feasibility and acceptability of collecting dried blood spots (DBS) from children after vaccination during Supplementary Immunization Activities to estimate measles and rubella seroprevalence

“…While we did not find evidence of the blood collection affecting vaccination campaign uptake, there was lower vaccination coverage for the 2020 November SIA compared to 2016. However, this was seen nationally and believed to be due to the COVID-19 pandemic (15). Because this was the first experience conducting a serosurvey during a vaccination campaign, it was important to evaluate the implementation.…”

“…According to the post-campaign coverage survey, vaccination coverage for the campaign in Copperbelt Province, where Ndola District is located, was 79%, higher than the national coverage of 68%. Southern Province, where Choma District is located, was comparable to the national average (65%) (15). While there were misconceptions about the reasons for blood collection, staff believed these could be overcome with dissemination of more information.…”