Apple and Google announced a significant new step in their collaboration to help public health authorities track and trace COVID-19 exposures using smartphones. The companies say they’re ready to send out an application programming interface (API) that could let health agencies enlist the help of millions of smartphones in tracking the spread of COVID-19 from person to person.

The API will let health agency apps use the Bluetooth in iOS and Android phones to detect and remember other smartphones that they’ve come near, in case the owner of one of the devices later proves to have COVID-19. Then the health agency would be able to notify the device’s owner that they’ve potentially been exposed. Apple and Google said that “a number of” U.S. states have asked for access to their API, but declined to give an exact number.

The two companies held a press call Wednesday to announce the API release, and to address some of the privacy concerns about their contact tracing framework. With any tech platform that sets out to track users, privacy and security will be major concerns. While Apple and Google appear to have built in a fairly elaborate system of safeguards into the design, how long the tracking data is kept and how it’s used later on is worth watching. But there’s a larger, more immediate issue.

What’s more pressing is whether a critical mass of people will actually use the health authority apps to make a difference in the fight against the virus. An Oxford University study found that for contact tracing programs to significantly slow the spread of disease, 60% of the population must participate (although, it said, even a 20% participation rate might yield useful insights). A Washington Post/University of Maryland survey found that three in five Americans probably wouldn’t participate in a digital contract tracing program developed by large tech companies.

That’s probably why representatives from Apple and Google spent a good amount of time on the press call emphasizing that the tech companies are merely providing an “enabling” technology, and that it’s the health agencies that will be building the apps and making the decisions on when and how to contact the exposed.

On one level, that’s smart. The two tech companies are involved in healthcare tech, but they should default to the experts at the health agencies in epidemiological matters. They may also be aware that people are more likely to trust a public health agency to track and trace than a big tech company, especially one like Google that’s in the business of harvesting personal data.

But though providing an enabling API is a significant contribution, it probably won’t be enough to make contact tracing apps a helpful tool in reducing virus spread. Look at Utah: The state paid $2.75 million for its own app, turned it on in mid-April, and so far only 45,000 of the state’s 3.2 million people have downloaded it, Buzzfeed News reports.

It might help that sometime this summer, Apple and Google plan to build the contact tracing technology into their respective mobile operating systems, which is something like the Amber Alerts you can opt into or out of in iOS. This will “allow more individuals to participate . . . as well as enable interaction with a broader ecosystem of apps and government health authorities,” Apple said in a press release last Month.

However, if the companies want the contact tracing apps to be successful, they will likely have to do more than enable the apps on a technical level behind the scenes.

Apple and Google have another tool at their disposal: they can leverage the vast reach and marketing power of their mobile platforms to educate people on how digital contract tracing works without location tracking or other threats to privacy, and how health officials use the contract tracing data. Education, it turns out, is a big component of this—and it may be just as important as the technology.

“Potentially problematic but probably surmountable is the amount of misunderstanding about the technology,” says Cornell University government professor Sarah Kreps, who just managed a large national survey on people’s perceptions of digital contact tracing. “Large proportions of the population are convinced that either ‘Big Tech’ or ‘Big Government’ is out to steal their data or spy on them.”

“It will be important to combine the eventual roll-out of the app with a public health campaign that educates the public about the tech features that guard against potential misuse of data,” Kreps says.

Apple and Google could play a crucial part in that campaign. Along with sending users notifications and putting ads in their respective app stores encouraging people to download their health authority’s app, the companies should use their big marketing budgets to tell the story of digital contact tracing. They should produce ads and social media content showing how public officials use the smartphone tracing data to notify people who’ve been exposed to COVID-19 cases.

Apple already likes to tell the stories of people whose lives were saved by the health features in their Apple Watch; it needs to tell similar stories about contact tracing. Both companies should provide examples of real people who were thankful to be traced before they inadvertently spread the infection to their families. And if the apps they support prove to be successful in some areas, Google and Apple should tell the stories of cities that hit their contact tracing thresholds using apps enabled by their technology and were therefore able to reopen.

Above all, the tech companies—especially Apple, which holds a certain public trust—should double down on promoting contact tracing this summer. They should not just enable it, but own it. Only then will the companies’ work get the reach and scale needed to make a real difference.