The Lancet: COVID-19 pandemic interrupted routine vaccinations for at least 17 million children worldwide in 2020, modelling study suggests

• Global and regional estimates of COVID-19’s impact on routine childhood immunisation indicates unparalleled disruptions in delivery of vaccines against measles (MCV1) and diphtheria, tetanus, and pertussis (whooping cough) (DTP3) – with 2020 coverage likely falling in some regions to levels not seen in over a decade.
• An estimated 8.5 million third doses of DTP vaccine and 8.9 million first doses of measles vaccine were missed by children worldwide in 2020—a relative decline of more than 7% over expected coverage levels had no pandemic occurred (83% expected global coverage vs 77% estimated due to pandemic disruption for third dose of DTP; 86% vs 79% for first dose measles vaccine).
• Estimates suggest twice as many children may have missed doses of each vaccine than expected due to pandemic disruptions in high income countries in Central Europe; Eastern Europe, and Central Asia; and North Africa and the Middle East.
• Although child vaccination rates improved in later months of 2020, catch-up efforts are lagging, and authors warn that the world may face a resurgence of vaccine-preventable diseases unless a concerted effort is taken to get routine immunisation services back on track.

The COVID-19 pandemic may have resulted in the largest and most widespread global disruption to life-saving immunisation programmes in history, putting millions of children—in rich and poor countries alike—at risk for measles, diphtheria, tetanus, and pertussis (whooping cough), according to a new modelling study published in The Lancet.

The study estimates that global coverage for the first dose of measles vaccine (MCV1) and coverage for the third vaccine dose against diphtheria, tetanus, and pertussis (DTP3) may both have fallen below 80% in 2020—a relative decline of at least 7% below expected levels for both vaccines had the pandemic not occurred (table 1). Combined with disruptions to planned mass vaccination campaigns in 2020, these declines in routine vaccination could increase the risk of future measles outbreaks and deaths, researchers say.

Although the findings suggest that by December 2020 monthly doses administered worldwide began nearing expected levels, the authors warn that ongoing COVID-19 transmission, the emergence of new variants, and a focus on COVID-19 vaccine rollout could easily stall or reverse these positive trends.

They stress that without concerted catch-up and expansion efforts, especially as populations increasingly return to social mixing, the world will face heightened risks of outbreaks of vaccine-preventable infectious diseases like measles and whooping cough.

The authors used human mobility data to estimate vaccine coverage in countries where data were not available. Changes in mobility patterns relative to pre-pandemic levels reflect how people changed behaviours during the course of the pandemic so can be used as a proxy for broader societal disruptions related to COVID-19 pandemic, like vaccine delivery. But the authors caution that their estimates are based on assumptions that might impact the accuracy of the estimates.

“Many health systems around the world are still under immense pressure coping with COVID-19, and are working hard to roll out new vaccination programmes. But it’s imperative that routine childhood vaccinations, that save the lives of millions of children each year, are not forgotten. Without renewed efforts, these preventable diseases could rebound in force. Countries must use every opportunity to close immunisation gaps”, says senior author Assistant Professor Jonathan Mosser from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington’s School of Medicine, USA. [1]

Lead author Kate Causey, a researcher at IHME, adds, “Even before the pandemic, millions of children worldwide were not receiving doses of routine vaccines. Those numbers have declined dangerously since the pandemic, with coverage in 2020 falling to levels not seen for over a decade. Although vaccination rates are rebounding, simply returning to pre-pandemic levels of vaccine coverage will still leave millions of children at risk for vaccine-preventable diseases that pose a serious threat to their health and survival.” [1]

Official vaccine disruption data from WHO and UNICEF, also published this week, shows a similar picture of declines in coverage for childhood vaccines.

The reasons for vaccine disruptions vary. Lockdowns made it harder for vaccinators and parents to reach immunisation sessions, while fear of contracting COVID-19 kept some parents away. At the same time, health workers were diverted to COVID-19 response duties, alongside a lack of protective equipment and vaccine supply chain problems [2].

Measles, diphtheria, tetanus, and pertussis are four vaccine-preventable childhood diseases targeted by immunisation programmes around the world, with measles claiming the lives of over 207,000 people in 2019 [3]. Previous studies have demonstrated the short-term impact of the COVID-19 pandemic on childhood vaccine delivery and disease burden in specific locations and/or time periods only. Furthermore, accurately measuring COVID-related disruptions to routine immunisations can be challenging due to often delayed and incomplete data reporting during the pandemic.

To address this, researchers used country-reported data and electronic medical records on vaccine administration to estimate the pandemic’s impact on global and regional vaccine doses delivered and coverage for MCV1 and DTP3 during each month in 2020. They built a model using daily human movement data captured through anonymised tracking of mobile phones in 134 countries to generate projections and estimate disruption to vaccine delivery in 100 countries where monthly vaccine administration data were not available.  

The researchers also modelled the number of doses expected to be given in 2020 had the COVID-19 pandemic not happened. By comparing the estimated number of doses given during the pandemic to the number expected in 2020 without the pandemic, they estimated the number of additional children who missed routine doses throughout 2020 attributable to COVID-19.

The findings suggest that South Asia was the most acutely affected region in 2020, with an estimated 3.6 million doses of DTP3 and 2.2 million doses of MCV1 vaccine missed by eligible children due to the pandemic—almost twice as many as expected (table 1). Regional coverage of DTP3 was estimated to have fallen by 13% and MCV1 by 4%, relative to expected levels.

Similarly, in high-income countries the number of children who missed doses of each vaccine more than doubled due to pandemic disruptions in 2020—with missed doses of DTP3 rising from an expected 600,000 to an estimated 1.2 million; and missed doses of MCV1 from 700,000 to 1.5 million (table 1).

Disruptions to vaccine delivery in 2020 were lowest in sub-Saharan Africa, where coverage was estimated to have declined by around 4% in 2020, equivalent to an additional 900,000 children not vaccinated with DTP3 and 1.1 million without MCV1. The authors emphasise, however, that many countries in sub-Saharan Africa had lower baseline routine vaccination coverage prior to the pandemic and rely on periodic mass vaccination campaigns to prevent outbreaks of diseases like measles. In these countries, the risk of outbreaks may remain high, even if disruptions to routine services were minimal.

Aligned with surveys conducted during the course of the year, the results indicate that April 2020 had the largest number of children missing doses, with global disruptions exceeding 30% (table 1).

However, the second half of 2020 showed signs of recovery, with global monthly doses delivered nearing expected levels by December. Nevertheless, overall uptake remained substantially reduced, with an estimated 8.5 million children who might have missed a third dose of DTP and 8.9 million missing a first dose of MCV due to pandemic disruptions in 2020.

“Continued recovery of routine immunisation services is far from inevitable”, says Causey. “Countries have embraced innovative approaches to reach children with safer vaccination services, including through home visits, using schools and supermarkets, drive-thru, and extending opening hours. We have an invaluable opportunity to learn from these adaptive efforts and strengthen data systems to guide broader catch-up efforts that also target unvaccinated children and underserved communities, and to build more equitable, sustainable vaccine services for all children, and improve child health more broadly for generations to come.” [1]

The researchers note that there are important limitations to their study, including that mobility measures are imperfect proxies for the pandemic’s broader societal effects and may not fully represent changes in vaccination delivery across locations and over time. They also highlight that changes in country-reported data on vaccine doses administered may not correspond with changes in coverage, because they generally exclude doses delivered outside of target schedules and supplemental immunisation activities, and therefore may not fully capture catch-up vaccination efforts. Finally, they note that they were unable to fully account for potential reporting delays or data quality challenges associated with the ongoing pandemic. As additional data become available research will update these estimates to improve understanding of COVID-19’s impact on routine immunisation in 2020 and beyond.

The study was funded by the Bill & Melinda Gates Foundation. It was conducted by researchers at the University of Washington, Seattle, USA; World Health Organisation, Geneva, Switzerland; Pan American Health Organization, Washington DC, USA; and Seattle Children’s Hospital, Seattle, USA.

[1] Quotes direct from authors and cannot be found in the text of the Article.
[2] https://cdn.who.int/media/docs/default-source/immunization/gin/gin-june-2020.pdf?sfvrsn=732b5fe5_3&download=true 
[3] Worldwide measles deaths climb 50% from 2016 to 2019 claiming over 207 500 lives in 2019 (who.int)