SARS-CoV-2 infection risk during delivery of childhood vaccination campaigns: a modelling study

BACKGROUND

The COVID-19 pandemic has disrupted delivery of immunisation services globally. Many countries have postponed vaccination campaigns out of concern about infection risks to staff delivering vaccination, the children being vaccinated and their families. The World Health Organization recommends considering both the benefit of preventive campaigns and the risk of SARS-CoV-2 transmission when making decisions about campaigns during COVID-19 outbreaks, but there has been little quantification of the risks.

METHODS

We modelled excess SARS-CoV-2 infection risk to vaccinators, vaccinees and their caregivers resulting from vaccination campaigns delivered during a COVID-19 epidemic. Our model used population age-structure and contact patterns from three exemplar countries (Burkina Faso, Ethiopia, and Brazil). It combined an existing compartmental transmission model of an underlying COVID-19 epidemic with a Reed-Frost model of SARS-CoV-2 infection risk to vaccinators and vaccinees. We explored how excess risk depends on key parameters governing SARS-CoV-2 transmissibility, and aspects of campaign delivery such as campaign duration, number of vaccinations, and effectiveness of personal protective equipment (PPE) and symptomatic screening.

RESULTS

Infection risks differ considerably depending on the circumstances in which vaccination campaigns are conducted. A campaign conducted at the peak of a SARS-CoV-2 epidemic with high prevalence and without special infection mitigation measures could increase absolute infection risk by 32% to 45% for vaccinators, and 0.3% to 0.5% for vaccinees and caregivers. However, these risks could be reduced to 3.6% to 5.3% and 0.1% to 0.2% respectively by use of PPE that reduces transmission by 90% (as might be achieved with N95 respirators or high-quality surgical masks) and symptomatic screening.

CONCLUSIONS

SARS-CoV-2 infection risks to vaccinators, vaccinees and caregivers during vaccination campaigns can be greatly reduced by adequate PPE, symptomatic screening, and appropriate campaign timing. Our results support the use of adequate risk mitigation measures for vaccination campaigns held during SARS-CoV-2 epidemics, rather than cancelling them entirely.

Measles and rubella vaccination coverage in Haiti, 2012: progress towards verifying and challenges to maintaining measles and rubella elimination

OBJECTIVES

We conducted a nationwide survey to assess measles containing vaccine (MCV) coverage among children aged 1-9 years in Haiti and identify factors associated with vaccination before and during the 2012 nationwide supplementary immunisation activities (SIA).

METHODS

Haiti was stratified into five geographic regions (Metropolitan Port-au-Prince, North, Centre, South and West), 40 clusters were randomly selected in each region, and 35 households were selected per cluster.

RESULTS

Among the 7000 visited households, 75.8% had at least one child aged 1-9 years; of these, 5279 (99.5%) households consented to participate in the survey. Of 9883 children enrolled, 91% received MCV before and/or during the SIA; 31% received MR for the first time during the SIA, and 50.7% received two doses of MCV (one before and one during the 2012 SIA). Among the 1685 unvaccinated children during the SIA, the primary reason of non-vaccination was caregivers not being aware of the SIA (31.0%). Children aged 1-4 years had significantly lower MR SIA coverage than those aged 5-9 years (79.5% vs. 84.8%) (P < 0.0001). A higher proportion of children living in the West (12.3%) and Centre (11.2%) regions had never been vaccinated than in other regions (4.8-9.1%). Awareness, educational level of the mother and region were significantly associated with MR vaccination during and before the SIA (P < 0.001).

CONCLUSIONS

The 2012 SIA successfully increased MR coverage; however, to maintain measles and rubella elimination, coverage needs to be further increased among children aged 1-4 years and in regions with lower coverage.