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

Abstract

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.

Keywords: COVID-19; SARS-CoV-2; healthcare workers; infection risk; outbreaks; supplementary immunisation activity; vaccination campaign.

Figure 1.

Modelled incidence (A), prevalence (B), and cumulative proportion of the population infected (C) for different R₀ assumptions.

Figure 2.. Modelled excess risk of (A) vaccinators and (B) children and/or caregivers becoming infected during fixed-post immunisation campaigns conducted at different times during the epidemic.

Results are shown for epidemics modelled using different R₀ assumptions. Line colour shows the impact of different levels of PPE effectiveness, and dashed lines show the combined impact of PPE together with symptomatic screening (assumed to screen out all symptomatic individuals.)

Figure 3.. Sensitivity analysis showing the impact of varying model input parameters on the peak value of excess infection risk to vaccinators.

The changes compared to the base case (in Table 1) are shown for the minimum (lighter shading) and maximum (darker shading) parameter values shown in Table 1, and for two different assumptions about PPE effectiveness.

Figure 4.. Sensitivity analysis showing the impact of varying model input parameters on the peak value of excess infection risk to children and their caregivers.

The changes compared to the base case (in Table 1) are shown for the minimum (lighter shading) and maximum (darker shading) parameter values shown in Table 1, and for two different assumptions about PPE effectiveness.