Impact of COVID-19 vaccination pausing on uptake

A recent study looks at the implications of pausing vaccinations against coronavirus disease 2019 (COVID-19) due to blood clotting concerns that occurred around mid-March 2021. While the vaccine's benefits outweigh the risks, the study findings suggest that the pause had no significant impact on the subsequent vaccine uptake in the European countries.

Study: The impact of pausing the Oxford-AstraZeneca COVID-19 vaccine on uptake in Europe: a difference-in-differences analysis. Image Credit: cortex-film/ ShutterstockStudy: The impact of pausing the Oxford-AstraZeneca COVID-19 vaccine on uptake in Europe: a difference-in-differences analysis. Image Credit: cortex-film/ Shutterstock


The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was first identified in December 2019 in Wuhan. Since then, it is responsible for over 4.54 million deaths globally. In an unprecedented timeframe, vaccines against the virus were developed and administered early on in 2020. However, reports of potential blood clot cases in a few vaccinated individuals questioned the safety of the vaccines.

By March 10, 2021, the European Medicines Agency (EMA) reported 30 cases of thromboembolic events among approximately 5 million individuals who were administered the Oxford-Astrazeneca COVID-19 vaccine in the European Economic Area (EEA). Despite the observation by EMA that the number of thromboembolic events in vaccinated people is not more than the number commonly seen in the general population, many European countries paused their rollouts of the Oxford AstraZeneca COVID-19 vaccine.

In a paper available on the preprint server medRxiv, Scientists from University College London investigated if this pause had any significant impact on the uptake of COVID-19 vaccines - specifically the Oxford-AstraZeneca vaccine.

A preprint version of the study is available on the medRxiv* server, while the article undergoes peer review.

The study

The scientists constructed a longitudinal panel for 28 EEA countries with the vaccine uptake data at three-week intervals from week 3 to 18 of the COVID-19 vaccination rollout in 2021. Because the UK is no longer in the EEA, it had different systems for the vaccine rollout. Denmark and Norway did not resume the vaccinations program after the pause. Therefore, the UK, Denmark, and Norway were not included in the study. The control group was the nine countries that did not pause the rollout of the Oxford-AstraZeneca vaccine.

The researchers obtained all the data (collected at the country level) from the European Centre for Disease Control and Prevention COVID-19 Vaccine Tracker and Open Data and the World Bank Open Database. They conducted the analysis using STATA 14 (Stata Statistical Software: Release 14. 2015).

The results showed that the COVID-19 vaccination trend in both groups was similar, with no deviation after the pause. However, there was a temporal shift away from using the Oxford-AstraZeneca vaccines in all EEA countries, though the uptake was not significantly different.

The scientists found that pausing the rollout of the Oxford-AstraZeneca vaccine resulted in a subsequent 0.52% decrease in the overall population uptake for the first dose of a COVID-19 vaccine and a 1.49% decrease in the uptake for both doses of the vaccine, comparing countries that paused to those that did not.

Looking at the uptake of the Oxford-AstraZeneca vaccine only, they found the estimates even lower: a 0.56% increase in uptake for the first dose and a 0.07% decrease in uptake for both doses.


Since these findings are not statistically significant, they suggest that the pause had no impact on subsequent vaccine uptake. For both one and two doses of the COVID-19 vaccine, and at the overall vaccine uptake (including all vaccines) and the OxfordAstraZeneca vaccine alone, after pausing the Oxford-AstraZeneca vaccine in mid-March, there was no difference in the vaccinations. Notably, this suggests that the public confidence in vaccination was unaltered due to the pause and concerns raised over the Oxford-AstraZeneca vaccine.

This analysis suggests that as new COVID-19 vaccines emerge, regulators should be cautious about deviating from usual pharmacovigilance protocols based on potential impacts on public confidence if further investigation on clinical or epidemiological grounds is warranted, the scientists conclude.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Dr. Ramya Dwivedi

Written by

Dr. Ramya Dwivedi

Ramya has a Ph.D. in Biotechnology from the National Chemical Laboratories (CSIR-NCL), in Pune. Her work consisted of functionalizing nanoparticles with different molecules of biological interest, studying the reaction system and establishing useful applications.


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