The coronavirus outbreak is bringing attention to the fast-growing vaccine industry.

The vaccine market has grown six fold over the past two decades, worth more than $35 billion today, according to AB Bernstein. The firm said the industry has consolidated to four big players that account for about 85% of the market British drug maker GlaxoSmithKline, French pharmaceutical company Sanofi, and U.S.-based Merck and Pfizer.

"For every dollar invested in vaccination in the world's 94 lowest-income countries, the net return is $44. Hard to argue against," Wimal Kapadia, Bernstein's analyst, said in a note. "This oligopoly has been built through significant market consolidation driven primarily by the complexities of the manufacturing and supply chain."

These companies have jumped into the race to combat the deadly coronavirus, working on vaccine or drug programs. Investors have been flocking to some biotech names amid market volatility in hopes that their initiatives to develop treatment and prevention for the coronavirus could come to fruition at some point.

Sanofi is teaming up with the U.S. government to develop a vaccine for the new virus, hoping its work on the 2003 SARS outbreak could speed up the process. GlaxoSmithKline said this month it is partnering with the Coalition for Epidemic Preparedness Innovations for a vaccine program. Still, any commercial treatment for the coronavirus could be years away. Experts have warned despite recent advances; the public shouldn't expect a coronavirus vaccine to hit the market until early next year.

The Bernstein analyst said Sanofi and GlaxoSmithKline both have a stable vaccine portfolio, including shingles, flu, pertussis and polio vaccines, that will keep driving revenue.

Question: Based on the article above about, describe the market structure of the vaccine industry (producers), and analyze critically the possible microeconomic problems and policies by applying the relevant microeconomic theories/ concepts.