With nearly three quarters of all adults fully vaccinated against Covid-19, the European Union is a world leader in inoculations. But the impressive headline number is obscuring an uncomfortable reality: the rollout has been extremely unequal across the union.

Some countries, including Ireland, Malta, Portugal and Denmark, have achieved near universal vaccination, boasting coverage rates of around 90%, according to the European Center for Disease Control (ECDC). On the other side of the bloc, Romania and Bulgaria have fully vaccinated only 33% and 22% of their adults, respectively.

The problem isn't down to vaccine shortages. All EU countries have access to all of the shots approved by the EU — Pfizer/BioNTech, Moderna, AstraZeneca, and Johnson & Johnson. Individual countries are also free to get other shots. Hungary, for example, has acquired Russian Sputnik vaccines for its population.

“They have the vaccines. Anybody who wants to get vaccinated can,” Ivan Krastev, a Bulgarian political scientist and a founding board member of the European Council on Foreign Relations, told CNN.

Instead, Krastev said, Bulgaria struggles with deep-seated vaccine hesitancy that is fueled by political instability, conspiracy theories and a lack of faith in the authorities.

“There's high level of mistrust, and that goes both for Bulgaria and Romania,” he said. “Even the medical community, doctors, nurses, many are hesitant to get vaccinated, so it's not a surprise that the society as a whole is too,” he said.

Both Romania and Bulgaria have been battling spikes in new coronavirus cases since early September. Romania has reported over 45,000 new cases and more than 800 deaths in the week to Sunday, about the same level it saw at the peak of its second wave of the epidemic in April.

The ECDC warned Thursday that states with low vaccination rates are risking surges in hospitalizations and deaths this fall if they relax social distancing measures.

“In such a scenario, due to very high virus circulation, fully vaccinated vulnerable populations are also at risk of experiencing infection with a severe outcome,” the ECDC said in its latest Covid-19 risk assessment, urging the countries that are struggling with inoculations to try to understand why their population remain hesitant and then address those issues.

Bulgaria is holding its third parliamentary election this year in November. Two previous votes, in April and then in July, ended in a stalemate, with no government formed. As a result, the country is stuck in a perpetual election campaign with little room for anything else.

“There has been much more election campaigning than vaccine campaigning,” Krastev said. “Neither the government that was in power nor the caretaker government made vaccination a priority.”

Krastev said the issue of vaccines hadn't divided Bulgarian society along partisan lines, because most people were generally united in their distrust of the political class. “The US has a major level of polarization; here it's not so much political polarization, but confusion and disgust with anything political that very much hurt the success of the [vaccination] campaign,” he told CNN.

Allegations of government corruption sparked widespread protests across Bulgaria last year. Police reacted with violence that shocked the nation — and made people even more suspicious of the authorities.

The media also played a role, Krastev said. “In order to make the debate more interesting, they would present the pro-vaccine and anti-vaccine opinions as equally valuable, so people get confused,” he said.

The Romanian government has blamed its poor vaccination rollout on fake news and conspiracy theories that are being spread online.

There are also stark inequalities within both countries. Roma communities in Romania and Bulgaria are among the least vaccinated. Dimitar Dimitrov, the director of the Roma Program at the Open Society Institute in Sofia, said the problem is down to strained relationships between the communities and wider society.

“Many Roma neighborhoods in Bulgaria have been subject to lockdowns without proper [explanation] even though the level of infections in other parts of the same municipalities has been higher. So this attitude from institutions towards Roma people and Roma neighborhoods shows why Roma don't trust institutions,” Dimitrov told CNN.

Dimitrov said many people, especially in rural areas, might also find it difficult to access vaccination clinics. “If you have to get a bus or train and travel 100 kilometers to get to the hospital and then wait in the line, that takes time and money. The vaccination itself is free but to get to the vaccination point costs money,” Dimitrov said.

The Romanian government recently announced it would put extra resources into ensuring people who can't access clinics are able to get the shots — for example by requesting a doctor to visit them at home.

The East-West divide

But Bulgaria and Romania aren't the only ones facing a hesitancy problem. The European Union appears to be divided into two parts. One half has embraced inoculation and got almost everyone immunized. The other is struggling to convince large numbers amid deep mistrust in the vaccines.

The dividing line sits roughly along the Iron Curtain boundary that once split Europe into East and West.

Of the bloc's 27 member states, the 15 top performers in terms of inoculation rates are all part of what used to be the Western bloc, while the bottom 10 are all former Communist countries. Greece and Lithuania are the only two countries bucking the trend, with Lithuania placing 16th and Greece 17th.

All of the former Western countries, with the exception of Greece, have fully vaccinated at least 70% of their adults. None of the Eastern states have reached that threshold yet.

Krastev said the way the pandemic unfolded across different countries could be one factor explaining the differences. “The countries that got hit by the first wave more, in 2020, when the shock was stronger, countries like Italy or Spain, they have more success with vaccination in general than the countries that were hit by the second wave,” he said, adding that the Bulgarian government never managed to convince people that a high vaccination rate was a top priority.

“Instead it became the matter of national pride that we never had lockdown,” he said.

Anna Nicińska, an assistant professor at the Faculty of Economic Sciences at the University of Warsaw, has studied the reasons for vaccine hesitancy and said that history also plays a major role in influencing people's decisions.

Nicińska and her colleagues looked at data on trust in health care systems and medical authorities from 100 countries and found that mistrust was much higher in nations that had experienced Soviet-style communism in the past. People who had had firsthand experience of being lied to by their governments struggled to trust the authorities, even years after revolution, she explained. The longer people lived under communism, the higher the mistrust.

“People exposed to Soviet Communism are less trustful in other people, the government and also the health care systems, [the experience] instills mistrust in the public domain and [anything] formal,” she said.

Nicińska said this was one reason why strict vaccine requirements may not lead to significantly higher uptakes in such countries.

“A vaccination decision is based on trust and making it compulsory would be counterproductive, you have to remember that in many countries there's a long tradition of resistance towards the state, so people would find a way to avoid compulsory vaccination.”

The European Commission has acknowledged the low vaccination rates in some of its member states as an issue.

“As long as the virus is not defeated in all member states, the virus is simply not defeated,” a Commission spokesperson told CNN in a statement. The Commission said countries that are struggling to boost vaccination levels should focus on campaigns specifically targeting those who are hesitant, and stress the importance of science.