Countries around the world are re-assessing and adjusting the use of two covid-19 vaccines (Oxford-AstraZeneca’s Vaxzevria/Covishield and Janssen’s Ad26.COV2.S) as reports of rare but severe clotting side effects emerge. Denmark has become the first country to completely withdraw either vaccine from their national covid-19 vaccination programme.1
Regulators in Europe (the European Medicines Agency and the Medicines and Healthcare products Regulatory Agency) and the World Health Organisation have reviewed data from countries that have administered more than 40m doses of the Vaxzevria vaccine so far, estimating that severe blood clots occur in 4-10 people out of 1m vaccinated.2
The data also show that Vaxzevria is effective at preventing hospitalisations, intensive care unit (ICU) admissions and deaths due to covid-19, though the benefits of vaccination rise with
increasing age and infection rates. As a precaution, some countries have started to advise against the use of Oxford-AstraZeneca’s vaccine in younger adults (30-39 years).3
Overall, though, in places with low infection rates, the same 1m vaccinations will still prevent more than 1,000 deaths and many more hospital and ICU admissions.4 The Janssen vaccine is only now starting to be used in the EU.5
A new study6 published in May 2021 (the first large observational study from Denmark and Norway which included 280,000 vaccine recipients) notes that there have been a small, but higher than expected number of venous blood clots in those who received Vaxzevria, equivalent to 11 excess cases per 100,000 vaccines. The number of more severe cases (venous blood clots in the brain) was very low, but also higher than what would be expected in the background population (~25 out of 1m vaccine recipients).
Scandinavian countries are known to harbour some of the most reliable and complete epidemiological data sources and therefore likely provide more accurate risk estimations. However, this doesn’t change the fact that even with the slightly higher risk found there compared to other countries, the absolute risks are still small when seen against the high number of serious cases of SARS-CoV-2 infections globally and the proven benefits of vaccination against covid-19.
The current pandemic has highlighted the challenges of risk communication both in general and especially during a global crisis during which authorities have to react and advise while scientific evidence is still being generated. As global news headlines are reporting Denmark’s choice to withdraw the concerned vaccines from the current national vaccine roll-out, it is vital to understand the decision from a broader perspective.
With around only ten new daily covid-19 cases per 100,000 population and completed vaccination of its most vulnerable groups (and around 15% of the entire population), Denmark
has controlled the pandemic relatively well compared with many other countries.7 As with other high-income nations, Denmark also has the option to choose from other vaccine suppliers since financial means and cold chain infrastructure are not an immediate challenge. In fact, the Vaxzevria vaccine only made up a relatively small proportion of the country’s vaccine portfolio even before it was withdrawn.8
Maintaining public trust in vaccination is a key concern
Understanding Denmark’s decision also requires background knowledge of its previous experience with vaccines. In 2014, Denmark saw a large drop from 90% to 54% in the uptake of
HPV vaccines through national vaccination programmes. This was due to alleged safety concerns raised by the media which were later refuted with scientific backing.9,10 This experience may have contributed to a particularly cautious course of action in the current situation.11 Danish authorities traditionally enjoy a high degree of public trust, and the wide public adherence to health regulations and advice during the pandemic, including high vaccine uptake, is seen as a major contributor to the country’s relatively successful pandemic response.
In other words, Denmark has withdrawn these two vaccines for the time being out of a so-called “extra caution principle”. This stance was adopted because the current covid-19 infection rate is relatively low, the country has alternative options for vaccine procurement and because authorities are abundantly sensitive to maintaining public trust and vaccine positivity.
However, it is not improbable that Denmark could reintroduce the vaccines if there is a resurgence of cases and better evidence to identify those most at risk of clotting. Paradoxically,
even though Denmark has reliable epidemiological data sources, identifying the subgroups at risk of clots will be challenging as they have a small population and have not used these vaccines as widely as other European countries. This evidence will need to come from other countries that have done so.
There are also ongoing discussions on making the existing stockpile of paused vaccines available on a voluntary basis. In a recent turn, Denmark has set up mechanisms to “lend” vaccines to neighbouring countries who continue to use them in their national programmes.
The importance of context in global health communication
While the decision to halt or withdraw the vaccines currently under investigation is based on sound local deliberations, such decisions, if not communicated with the appropriate context
through the media, may have public health repercussions on a global scale. It could ultimately jeopardise global vaccine uptake, particularly in places with insufficient pandemic control and limited access to—or choice of—covid-19 vaccines.
Over time, it will be important to quantify the comparative risk of side effects associated with these vaccines compared with those of other covid-19 vaccines. Individual risks must also be
carefully weighed against the potential consequences of stopping vaccine roll-out and public health risks at the societal and global levels.
Hopefully, through continued rigorous investigation and monitoring we will be able to collate all the evidence needed to inform best practice on the safe use of both current and future covid-19 vaccines. Alongside this, there is a need for transparent communications on how decisions are made.
The views and opinions expressed in this article are those of the author and do not necessarily reflect the views of The Economist Group or any of its affiliates. The Economist Group cannot accept any responsibility or liability for reliance by any person on this article or any of the information, opinions or conclusions set out in the article.
[1] https://www.sst.dk/en/English/Corona-eng/Vaccination-against-COVID-19
[2] https://www.ema.europa.eu/en/medicines/human/EPAR/vaxzevria-previously-covid-19-vaccine-astrazeneca#safety-updates-section and https://www.gov.uk/government/news/mhra-issues-new-advice-concluding-a-possible-link-between-covid-19-vaccine-astrazeneca-and-extremely-rare-unlikely-to-occur-blood-clots and https://www.who.int/news/item/16-04-2021-global-advisory-committee-on-vaccine-safety-(gacvs)-review-of-latest-evidence-of-rare-adverse-blood-coagulation-events-with-astrazeneca-covid-19-vaccine-(vaxzevria-and-covishield)
[3] https://www.gov.uk/government/news/jcvi-advises-on-covid-19-vaccine-for-people-aged-under-40
[4] https://www.ema.europa.eu/en/news/astrazenecas-covid-19-vaccine-benefits-risks-context
[5] https://www.ecdc.europa.eu/en/publications-data/data-covid-19-vaccination-eu-eea
[6] Pottegard A et al. Arterial events, venous thromboembolism, thrombocytopenia, and bleeding after vaccination with Oxford-AstraZeneca ChAdOx1-S in Denmark and Norway: population based cohort study. BMJ, 2021. 373: p.n1114
[7] https://www.sst.dk/en/English/Corona-eng/Status-of-the-epidemic/COVID-19-updates-Statistics-and-charts
[8] https://vaccinetracker.ecdc.europa.eu/public/extensions/COVID-19/vaccine-tracker.html#distribution-tab
[9] Suppli, C et al. Decline in HPV-vaccination uptake in Denmark - the association between HPV-related media coverage and HPV-vaccination. BMC Public Health, 2018. 18(1): p. 1360.
[10] Hviid A et al. Association between quadrivalent human papillomavirus vaccination and selected syndromes with autonomic dysfunction in Danish females: population based, self-controlled, case series analysis. BMJ, 2020. 370: p. m2930.
[11] “Is the AstraZeneca vaccine safe? The clear answer does not exist, and we must live with it, says professor”, April 2021 https://www.zetland.dk/historie/sejv9ZmA-ae6Ewl5D-3f72d
