An extra four million health workers are needed if global health is going to improve over the next decade, a group of 100 health leaders says.
The lack of health workers is particularly acute in parts of Africa
The Joint Learning Initiative, which includes the World Health Organization, said a lack of investment is limiting the chance of tackling disease.
The study said sub-Sahara Africa needed one million workers to fight conditions such as HIV, Aids, malaria and TB.
One reason for the shortage is that rich nations poach doctors and nurses.
Poor and politically struggling countries had been hit the hardest, making international reinforcement essential, the report, published in the Lancet medical journal, said.
There are more Malawian doctors in the British city of Manchester than in Malawi, the report said, while 550 of the 600 doctors trained in Zambia since independence have gone abroad.
There are estimated to be more than 100 million people working as health professionals across the world - of which 24 million are doctors, nurses and midwives while the rest are community and voluntary workers.
Sub-Saharan Africa has a tenth of the doctors and nurses for its population as Europe does.
Italy has 50 times as many health professionals per head as Ethiopia.
The report's co-author Lincoln Chen, of Harvard University, said individual countries needed to draw up strategies with the support of the international community.
"Nearly all countries are challenged by worker shortage, skill mix imbalance, misdistribution, negative work environment and weak knowledge base.
"It is impossible to underestimate the importance of a response to this call for action.
"At stake is nothing less than completing the unfinished agenda in health of the past century, while addressing the historically unprecedented health challenges of this new century."
Benefits of new treatments and vaccines
risk not being realised, the report warned.
WHO assistant director general Dr Tim Evans, who also co-authored the report, said the international community and national governments needed to address the issue.
And he warned: "Much child mortality could be prevented with existing treatment and medication but it is not happening because we do not have the workforce to provide these."
Damian Personnaz, a spokesman for Unicef, would not comment on the four million figure but said there was a desperate need for more health workers across all parts of the globe.
But he added: "It is not just a question of numbers. There needs to be better awareness, communication and training.
"Local populations can be trained to provide some medical treatment and having vaccine programmes and health staff in a country is no use if people do not know they are there."