A leading humanitarian group is blasting Pfizer (PFE) and GlaxoSmithKline (GSK) for what it says is a refusal to lower the price of their pneumonia vaccines, making it harder to treat refugee children in Greece and in other countries with vulnerable populations.

Doctors Without Borders/Médecins Sans Frontières (MSF), which has vaccinated more than 5,000 refugee children in detention centers and other camps across Greece, is calling on the drugmakers to slash their prices.

In Greece, MSF buys a single dose of the pneumonia vaccine from local pharmacies for 60 euros (about $66), with children requiring three doses for maximal protection. That is about 20 times more than the lowest price for the vaccine in other countries, where a dose costs about about $3.10, according to the group.

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Pfizer and GSK are the only two makers of the pneumococcal conjugate vaccine. Pfizer's Prevenar 13 is the world's best-selling vaccine. It protects infants and toddlers from more than a dozen types of Streptococcus pneumoniae, the bacteria that can cause pnemonia and meningitis, along with other ailments.

"It's just laughable that [Pfizer and GSK] can't take some steps toward affordability for children, and it's laughable that they can't find a solution for a humanitarian context," said Kate Elder, vaccines policy adviser with MSF. "It is condemnable that they price their vaccine so far out of reach for non-governmental organizations that are there to protect refugee children."

In the U.S., the Centers for Disease Control and Prevention recommends that all children younger than 5-years-old (and adults 65 years or older) are vaccinated against pneumonia.

A young girl and her mother shelter from the rain as they wait at a refugee camp at the Greek-Macedonia border on March 04, 2016, in Idomeni, Greece. Dan Kitwood/Getty Images

Globally, pneumonia is the biggest killer of children under age 5. Because the bacteria is spread through close contact with someone who is infected with pneumococcus, including coughing and sneezing, refugee camps and other humanitarian crises are a prime vector for these diseases.

Pfizer defends its pricing policy for the company's pneumonia drug, saying it is costly and laborious to produce. "Prevenar 13 is one of the most complex biologics ever developed and it takes 2.5 years to make a single dose," the company said in a statement.

Pfizer said it provides Prevenar 13 for $3.30 a dose in countries that are eligible for lower prices under the so-called Gavi vaccine alliance, a public-private group that since 2000 has sought to increase access to the drugs in poor countries.

"We help address humanitarian crises through donations of Prevenar 13 to humanitarian organizations," the company said, adding that it is in discussions with the group to determine if more vaccine supplies are needed.

GSK said it would lose money on each dose of its Synflorix vaccine if lowered its price as much as much as Doctors Without Borders is calling for.

"For us to be able to continue to supply vaccines in the long-term and to continue to widen access to vaccines to protect people from serious disease, we need to be able to cover our costs and ensure we have a sustainable business for the long-term," the company said in a statement.

Pfizer said it plans to reduce the price of Prevenar 13 to $3.10 for multi-dose vials in Gavi-eligible countries early next year. GSK in March offered to cut the price of Synflorix for Gavi to $3.05 per dose.

That may do little for the millions of refugees who in recent years have fled Afghanistan, Iraq, Syria and other countries that aren't classified as being eligible for the Gavi vaccine discount. More than 65 million people around the world have had to leave their countries, including 21.3 million refugees, according to UNHCR, the United Nation's refugee agency.

In recent years, many of those refugees have landed on the Greek islands of Chios, Kos, Leros, Lesbos and Samos, where thousands remain in detention camps. MSF has provided vaccinations on Samos and, in conjunction with Greek health officials, plans to offer similar care on Lesbos and at camps in the Epirus region within a matter of weeks, Elder said.

The organization has also vaccinated thousands of children at refugee camps in Idomeni in northern Greece and in the Attica region in the central part of the country.

Still, the public health challenge remains enormous. Most of the refugees who left their homes in Afghanistan, Iraq and Syria had little access to health care even before fleeing, Elder said. Those who make it to Greece, most passing through Turkey and making a dangerous voyage in makeshift boats across the Aegean Sea, find crowded, unsanitary camps with a shortage of medical staff. Many refugees also lack proper documents, another obstacle to getting care in Greece.

"You still have lots of people living in close quarters for a long time with poor access to health care," said Tania Karas, a freelance journalist based in Athens who focuses on refugee issues, noting that conditions in Greece's camps remain poor.

Elder said Doctors Without Borders has been urging Pfizer and GSK to negotiate a lower price for their pneumonia drugs for six years. But the companies have declined to reduce those costs, according to the group. A rival firm, the Serum Institute of India, is developing a competing pneumonia vaccine and has committed to selling it for $2 per dose, or $6 per child, Elder said.

MSF wants the drugmakers to cut the price for their pneumonia vaccines to $5 per child for all three doses in developing countries and in parts of the world beset by armed conflicts and other crises.

"We think that's an attainable price in humanitarian context for developing countries," she said.