According to the commission, nearly half a billion children have been immunised since 2000, thanks to funding from donors such as the EU, resulting in six million saved lives.
Barroso, who announced the funding at an event hosted by the European commission, said, "It is horrible and unacceptable that around 1.5 million children still die each year from diseases which could be prevented by a simple vaccine.
"That's why [Tuesday's] announcement of further EU funding is so important - it shows that we are committed, in the long term, to doing all we can to make sure that more men, women and children have access to life saving vaccines, no matter where they live," the Portuguese official explained.
The funding will go to the non-profit organisation GAVI alliance, which focuses on increasing access to immunisation in poor countries.
"Vaccines are the cheapest and the most cost-effective way of saving lives; they fight against disease before it has a chance to attack, and they give people the chance to live in dignity, free from pain and suffering," said Barroso.
"This applies to people not just in areas of peace, but also in areas of conflict, where people need protection the most.
"Through the bravery of doctors, nurses and health workers, we managed, for example, to help Yemen to reach two thirds of the children with essential immunisation. And we have had similar successes elsewhere, namely in Africa.
"I couldn't be more proud of what Europe does for citizens across the world, especially in these testing times," he said.
But, he continued, "Despite all our efforts, millions of people are still dying worldwide from diseases we have the knowledge to prevent.
"The cost of immunisation is also increasing due to the arrival of combination vaccines, the cost of transportation to increasingly remote areas, and storage. And there is also a need to increase awareness, increase training and find a way to tackle the global shortage of health workers."
He also highlighted the importance of investment in research and innovation, "because we still don't have the answers to all the challenges we face, including some of the most infectious diseases such as malaria and dengue fever".
"Nearly one billion people worldwide are affected by neglected infectious diseases, some with a fatality rate of 100 per cent, with very few drugs available.
"We understand that we all need to do more, and I would like also to call on others to increase their contributions for this critically important cause," he concluded.
Speaking on behalf of the GAVI alliance, Dagfinn Høybråten, chair of the organisation's board, said, "We are grateful to the European Union for more than doubling its contribution which will enable GAVI alliance to get closer to its goal of hugely increasing its impact by 2020, protecting millions more children against deadly diseases in the poorest countries."
He continued, "The European Union by committing additional funds to the current and the next funding cycle is showing its support to GAVI's mission which is closely aligned with European Union's development policy to reduce poverty and build sustainable development through inclusive growth."
Eloise Todd, international advocacy director of ONE, responded to the announcement saying, "president Barroso and [development] commissioner [Andris] Piebalgs deserve great credit for more than doubling the [commission's] contribution to GAVI in the context of an overall budget freeze.
"The €15m additional funding annually from the commission could mean that 840,000 more children could be provided with three key vaccines to protect against some of the biggest killers each year," she said.
"The [commission] has also added additional funds to GAVI in 2014 and 2015 and made a long-term commitment through to 2020, making today's pledge worth a total of €175m.
"We want other donors to follow the example of the EC and scale up their GAVI contributions," urged Todd, adding, "We also hope that the commission leaves the door open to future investments to GAVI, one of the most effective life-saving mechanisms in development."
Meanwhile, Andrew Witty, CEO of pharmaceutical giant GSK, said, "The achievements of the GAVI alliance are remarkable, with six million lives saved since its formation in 2000.
"Successful vaccination programmes have no doubt also helped countries to develop in this time," he finished.