The Oxford/AstraZeneca COVID-19 vaccine, approved for emergency use by the World Health Organization in February, has been causing controversy after it was revealed that some vaccinated individuals have been experiencing reactions causing blood clots to form in the brain. Distribution of the vaccine has been halted in many countries in fear of further diagnosis.

Suspicions regarding the rapidly-produced COVID-19 vaccines have already been rampant, and the news about the AstraZeneca vaccine only heightened them. The vaccine is most prominently used in Europe, where a third wave of the pandemic is already taking place and new strains of the virus are spreading.

“It takes a while to build up confidence in a vaccine which [the global health community] did with rigorously conducted trials, with really good safety data, with being open and transparent about what we did and didn’t find,” Michael Head, a senior research fellow in global health at the University of Southampton, told CNN. “When we have widespread withdrawal of the vaccine across multiple countries, in some countries that are quite vaccine-hesitant anyway, it might take a long time to rebuild that confidence.”

After much investigation, the European Medicines Agency declared the injection safe for resumed administration. The continent’s top drug regulator stated that the benefits of the shot exceeded the disadvantages. Cases of blood clotting were also found in a very small percentage of those vaccinated; in Germany, for example, only 13 cases of the condition (known as cerebral venous sinus thrombosis, or CVST) were diagnosed out of 1.6 million people who have taken the vaccine. It was also discovered that CVST can be easily treated with blood thinners and immunoglobulins. 

Many European leaders attempted to regain their citizen’s confidence in the vaccine. French prime minister Jean Castex and UK prime minister Boris Johnson both publicly endorsed the vaccine by getting it themselves and encouraging their citizens to as well. 

The AstraZeneca situation may increase people’s distrust in the COVID-19 vaccines, and could even lengthen the pandemic even further.