Estimating global and regional disruptions to routine childhood vaccine coverage during the COVID-19 pandemic in 2020: a modelling study

Abstract

Background: The COVID-19 pandemic and efforts to reduce SARS-CoV-2 transmission substantially affected health services worldwide. To better understand the impact of the pandemic on childhood routine immunisation, we estimated disruptions in vaccine coverage associated with the pandemic in 2020, globally and by Global Burden of Disease (GBD) super-region.

Methods: For this analysis we used a two-step hierarchical random spline modelling approach to estimate global and regional disruptions to routine immunisation using administrative data and reports from electronic immunisation systems, with mobility data as a model input. Paired with estimates of vaccine coverage expected in the absence of COVID-19, which were derived from vaccine coverage models from GBD 2020, Release 1 (GBD 2020 R1), we estimated the number of children who missed routinely delivered doses of the third-dose diphtheria-tetanus-pertussis (DTP3) vaccine and first-dose measles-containing vaccine (MCV1) in 2020.

Findings: Globally, in 2020, estimated vaccine coverage was 76·7% (95% uncertainty interval 74·3-78·6) for DTP3 and 78·9% (74·8-81·9) for MCV1, representing relative reductions of 7·7% (6·0-10·1) for DTP3 and 7·9% (5·2-11·7) for MCV1, compared to expected doses delivered in the absence of the COVID-19 pandemic. From January to December, 2020, we estimated that 30·0 million (27·6-33·1) children missed doses of DTP3 and 27·2 million (23·4-32·5) children missed MCV1 doses. Compared to expected gaps in coverage for eligible children in 2020, these estimates represented an additional 8·5 million (6·5-11·6) children not routinely vaccinated with DTP3 and an additional 8·9 million (5·7-13·7) children not routinely vaccinated with MCV1 attributable to the COVID-19 pandemic. Globally, monthly disruptions were highest in April, 2020, across all GBD super-regions, with 4·6 million (4·0-5·4) children missing doses of DTP3 and 4·4 million (3·7-5·2) children missing doses of MCV1. Every GBD super-region saw reductions in vaccine coverage in March and April, with the most severe annual impacts in north Africa and the Middle East, south Asia, and Latin America and the Caribbean. We estimated the lowest annual reductions in vaccine delivery in sub-Saharan Africa, where disruptions remained minimal throughout the year. For some super-regions, including southeast Asia, east Asia, and Oceania for both DTP3 and MCV1, the high-income super-region for DTP3, and south Asia for MCV1, estimates suggest that monthly doses were delivered at or above expected levels during the second half of 2020.

Interpretation: Routine immunisation services faced stark challenges in 2020, with the COVID-19 pandemic causing the most widespread and largest global disruption in recent history. Although the latest coverage trajectories point towards recovery in some regions, a combination of lagging catch-up immunisation services, continued SARS-CoV-2 transmission, and persistent gaps in vaccine coverage before the pandemic still left millions of children under-vaccinated or unvaccinated against preventable diseases at the end of 2020, and these gaps are likely to extend throughout 2021. Strengthening routine immunisation data systems and efforts to target resources and outreach will be essential to minimise the risk of vaccine-preventable disease outbreaks, reach children who missed routine vaccine doses during the pandemic, and accelerate progress towards higher and more equitable vaccination coverage over the next decade.

Funding: Bill & Melinda Gates Foundation.

Figure 1

Latest month of vaccine data availability in 2020 Data on either vaccine (DTP3 or MCV1) are shown. Locations coloured white did not have available month-specific data on MCV1 or DTP3 for 2020 at the time of analysis. The boundaries and names shown and the designations used on this map do not imply the expression of any opinion whatsoever on the part of WHO concerning the legal status of any country, territory, city or area or of its authorities or concerning the delimitation of its frontiers or boundaries. Dotted and dashed lines on maps represent approximate border lines for which there may not yet be full agreement. DTP3=diphtheria-tetanus-pertussis, third dose. MCV1=measles-containing vaccine, first dose.

Figure 2

Examples of model performance for step 1 (A) and step 2 (B), monthly mobility patterns (C), and monthly vaccine disruption patterns (D), from January to December, 2020 Step 1 involved modelling the relationship between cumulative disruptions in mobility and vaccine coverage (A), and step 2 involved modelling residual variation (B); more detail is available in the main text and in the appendix (section 4.1). Global model estimates are represented by solid grey lines; GBD super-region data and antigen-specific estimates are represented by light coloured data points and lines; and location-specific and antigen-specific data and estimates are represented by dark coloured data points and lines. The size of each data point corresponds with the inverse variance and weight in the model. In panel C, mean estimates of monthly mobility patterns are shown by solid lines. In panel D, mean estimates from step 1 are represented by dashed coloured lines and final combined model estimates are represented by solid lines; shaded areas represent 95% UIs for the final combined model, and error bars represent the 95% CIs for the monthly country data. Location-specific and antigen-specific examples were selected to reflect a range of model fits across different patterns of mobility and vaccine disruption, residual trends, and data availability. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study. DTP3=diphtheria-tetanus-pertussis, third dose. MCV1=measles-containing vaccine, first dose. UI=uncertainty interval.

Figure 3

Monthly vaccine coverage for DTP3 and MCV1, globally and by GBD super-region, from January to December, 2020 Solid lines show the estimated coverage by vaccine for each GBD super-region and globally by month, and the shaded area displays the 95% uncertainty interval. Dashed lines display the expected coverage for each vaccine in the absence of COVID-19. Estimated coverage can temporarily exceed 100% because of catch-up of children missed in earlier months. DTP3=diphtheria-tetanus-pertussis, third dose. MCV1=measles-containing vaccine, first dose. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study.

Figure 4

Estimated number of eligible children missing doses of DTP3 and MCV1 globally (A), and by GBD super-region (B), from January to December, 2020 The expected number of eligible children missing doses of DTP3 and MCV1 in the absence of the COVID-19 pandemic was calculated on the basis of past trends in coverage and the population for 2020 (and then divided by 12 for each month). Estimated doses missed reflect the number of children who were eligible to receive a given vaccine at some point during the year (ie, the target population) but did not receive it by the end of 2020. The proportion of total doses missed attributable to the COVID-19 pandemic was then calculated by subtracting total doses missed from expected doses missed on the basis of past trends. DTP3=diphtheria-tetanus-pertussis, third dose. MCV1=measles-containing vaccine, first dose. GBD=Global Burden of Diseases, Injuries, and Risk Factors Study.