LONDON, Jan 26 (Reuters) - Pfizer is to cut the price of its pneumococcal vaccine Prevenar 13 by 6 percent to $3.10 per dose in poor countries as part of a commitment to the GAVI global vaccines alliance, the U.S. drugmaker said on Monday.

Pfizer's move comes as GAVI holds a major funding conference in Berlin at which it hopes to raise $7.5 billion from donors to pay for increased deployment of vaccines in the developing world between 2016 and 2020.

The final amounted raised will be decided at the end of talks on Tuesday, although GAVI Chief Executive Seth Berkley said he was confident there would be enough money to immunise another 300 million children as planned.

"We still have some moving pieces but we are certainly close and we will be able to reach the kids we wanted to reach," he said in a telephone interview.

GAVI, which is backed by the Bill & Melinda Gates Foundation, the World Health Organisation, the World Bank, UNICEF, donor governments and others, funds immunisation programmes for nations that cannot afford standard prices.

Its bulk-buying power helps it negotiate big discounts, although some have argued it should strike tougher deals on prices. Charity Medecins Sans Frontieres (MSF) last week called for the price of pneumococcal vaccines to be slashed.

Pfizer vaccine head Susan Silbermann said its decision had been months in the making and was not related to MSF's demand.

The U.S. company's new lower per-dose price will be extended through 2025, even if developing countries with growing economies become too wealthy to be eligible for GAVI help.

GlaxoSmithKline also extended its price-freeze commitment to 10 years for countries graduating from GAVI support, while Sanofi promised to expand production of yellow fever vaccine to address chronic shortages.

(Reporting by Ben Hirschler. Editing by Jane Merriman)