WASHINGTON (Reuters) - Automakers in the United States repaired more than 7.2 million defective Takata air bag inflators in 2018, as companies have ramped up efforts to track down parts in need of replacement, a report from an independent monitor released on Friday said.

The logo of Takata Corp is seen on its display at a showroom for vehicles in Tokyo, Japan, February 9, 2017. REUTERS/Toru Hanai

Out of 37 million vehicles with 50 million inflators under recall, 16.7 million air bag inflators remain to be replaced. Average repair rates rose by 30 percent, said deputy National Highway Traffic Safety Administration chief Heidi King.

At least 23 deaths worldwide have been linked to the rupturing of faulty Takata air bag inflators, including 15 in the United States. The issue has sparked the largest auto industry safety recall in history, involving about 100 million inflators among 19 major automakers.

The issue will not end any time soon as automakers will add close to 10 million additional inflators to the record-setting recalls in January, said the report from monitor John Buretta.

More than 290 injuries worldwide have been linked to Takata inflators that can explode, spraying metal shrapnel inside cars and trucks.

To date, 21 deaths have been reported in Honda Motor Co 7267.T vehicles and two in Ford Motor Co F.N vehicles. Both automakers urged some drivers of older vehicles not to drive them until they got inflators replaced.

Repair rates for recalled 2006 Ford Rangers increased from 6 percent in January to 82 percent by October 2018, while recalled high-risk 2001–2003 Honda vehicles reached a repair rate of 96 percent, the report said.

Some automakers have canvassed neighborhoods in high-risk areas to try to find unrepaired models. The report also found that letters from state motor vehicle agencies had helped dramatically boost completion rates.

Additional exposure of inflators to high heat and humidity degrade the inflators, making them more prone to deadly ruptures.

“There is still a challenging road to travel ahead, and the clock is ticking for drivers and passengers with defective inflators still in their vehicles,” Buretta wrote.

The defect led Takata to file for bankruptcy protection in June 2017. In April, auto components maker Key Safety Systems completed a $1.6 billion deal to acquire Takata. The merged company is now known as Joyson Safety Systems and is a subsidiary of Ningbo Joyson Electronic Corp 600699.SS.