The impact of pausing the Oxford-AstraZeneca COVID-19 vaccine on uptake in Europe: a difference-in-differences analysis

  1. Vageesh Jain
  2. Paula Lorgelly

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Abstract

Background

Several countries paused their rollouts of the Oxford-AstraZeneca coronavirus disease-19 (COVID-19) vaccine in mid-March 2021 due to concerns about vaccine-induced thrombosis and thrombocytopenia. Many warned that this risked damaging public confidence during a critical period of pandemic response. This study investigated whether the pause in the use of the Oxford-AstraZeneca vaccine had an impact on subsequent vaccine uptake in European countries.

Methods

We used a difference-in-differences approach capitalizing on the fact that some countries halted their rollouts whilst others did not. A longitudinal panel was constructed for European Economic Area countries spanning 15 weeks in early 2021. Media reports were used to identify countries that paused the Oxford-AstraZeneca vaccine and the timing of this. Data on vaccine uptake were available through the European Centre for Disease Control and Prevention COVID-19 Vaccine Tracker. Difference-in-differences linear regression models controlled for key confounders that could influence vaccine uptake, and country and week fixed effects. Further models and robustness checks were performed.

Results

The panel included 28 countries, with 19 in the intervention group and 9 in the control group. Pausing the Oxford-AstraZeneca vaccine was associated with a 0.52% decrease in uptake for the first dose of a COVID-19 vaccine and a 1.49% decrease in the uptake for both doses, comparing countries that paused to those that did not. These estimates are not statistically significant (P = 0.86 and 0.39, respectively). For the Oxford-AstraZeneca vaccine only, the pause was associated with a 0.56% increase in uptake for the first dose and a 0.07% decrease in uptake for both doses. These estimates are also not statistically significant (P = 0.56 and 0.51, respectively). All our findings are robust to sensitivity analyses.

Conclusions

As new COVID-19 vaccines emerge, regulators should be cautious to deviate from usual protocols if further investigation on clinical or epidemiological grounds is warranted.

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  1. Version published to 10.1093/eurpub/ckac039
  2. ScreenIT

    SciScore for 10.1101/2021.08.30.21262821: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    Statistical Analysis: All analyses were conducted using STATA 14(17).
    STATA
    suggested: (Stata, RRID:SCR_012763)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Strengths and Limitations: We were able to answer this critical public health policy question using a natural experiment, requiring no manipulation to allocate the intervention. All included countries were part of the EEA and therefore to some extent comparable, and our statistical analyses accounted for important differences across groups of countries where present. The intervention itself occurred at approximately the same time across countries, with a direct and immediate impact on both public information and national vaccine programme rollouts, further supporting our approach. Outcome data were available from a single and reliable source (the ECDC) meaning our dataset was largely complete and of a high quality. Through investigating the impact on uptake for all vaccines as well as the Oxford-AstraZeneca vaccine specifically, our study was well designed to understand the various mechanisms through which the pause could have affected vaccine uptake. Our study had several limitations. First, although we were able to allocate countries to one of two groups, it is possible that there was contamination from the intervention to the control group. The European medicines regulatory system is based on a network of around 50 regulatory authorities from across EEA countries(30). Citizens may place more trust in their own national regulators compared with others. But populations in countries that did not pause the Oxford-AstraZeneca vaccine may have also been affected by knowing that ...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

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  3. Version published to 10.1101/2021.08.30.21262821v1 on medRxiv