Questions — and criticism — faced the European Commission head on Wednesday as she explained the EU's faltering vaccine rollout to the European Parliament.

Ursula von der Leyen is under pressure as EU states lag in the effort to inoculate their populations against COVID-19.

The Commission chief had previously acknowledged that the EU underestimated possible complications and delays in vaccine production.

What did von der Leyen say?

In the plenary session on Wednesday, the Commission president said the bloc had been too late to authorize vaccines and that it had placed too much confidence in vaccine suppliers.

"We were too late on the approvals. And perhaps we were too sure that what we ordered would actually arrive on time," von der Leyen said.

"We need to ask ourselves why this was the case and what lessons we can draw from this experience."

Von der Leyen defended the EU's joint procurement program, which saw the bloc order vaccines collectively.

"I cannot even imagine if just a handful of big players, big member states, had rushed to it and everyone else would have been left empty-handed. What would that have meant for our internal market and for the unity of Europe?"

Opening her address, von der Leyen said the vaccination campaign in Europe had gained momentum, with 26 million jabs given to 17 million people so far.

"We're going to work as hard as we possibly can to meet our objective so that at the end of the summer, 70% of the population will have been vaccinated," she added.

What have the problems been so far?

European Union leaders have faced public anger and scrutiny over the slow rollout of the immunization program in member states.

They became embroiled in heated public disputes with pharmaceutical companies over shortages in the supply of the vaccine.

In particular, von der Leyen criticized British-Swedish giant AstraZeneca amid major hold-ups at one of its EU production sites.  She accused the firm of falling short on contractual commitments to supply its vaccine to EU governments.

Details of confidential deals that were made public have cast doubt on the EU's ability to enforce contracts that were agreed upon on behalf of its members. In AstraZeneca's case, the firm has argued that it is only contractually bound to make its "best effort."

In a bid to stop vaccines being exported from the EU, the Commission briefly triggered an emergency Brexit deal clause. This jeopardized arrangements at the sensitive Irish border and was swiftly withdrawn after international outcry.

Critics accuse von der Leyen of relying on too narrow a circle of advisers and claim this tendency has proved counterproductive in such a complex crisis.

Extended and new lockdowns

By the start of this week, EU countries had given first vaccine doses to just under 4% of their populations, compared with 11% for the United States and nearly 17% for Britain.

Despite the start of vaccinations in EU nations, the virus is spreading more rapidly in some countries due to the spread of new variants. This has forced the reimposition or extension of lockdowns, adding to the pressure on the bloc's leadership.

A stricter lockdown is to be imposed in Greece from Thursday — in particular in the Athens region. Prime Minister Kyriakos Mitsotakis is warning that his country is facing a third COVID-19 wave.

Germany is expected to seek to extend strict curbs at least until the end of February amid an uncontrolled spread of highly contagious coronavirus variants from Britain and South Africa.

Europe has recorded a third of the more than 2.3 million lives lost globally to the virus.