WASHINGTON (AFP) - The United States on Tuesday (Dec 15) authorised its first rapid at-home test for Covid-19, which is available over-the-counter and produces a result in around 20 minutes.

The test, made by California-based Ellume, will sell for around US$30 (S$40) and the company plans to roll out three million units in January 2021, and millions more in subsequent months.

Stephen Hahn, commissioner of the Food and Drug Administration (FDA), said the emergency use authorisation represented a "major milestone."

"We are helping expand Americans' access to testing, reducing the burden on laboratories and test supplies, and giving Americans more testing options from the comfort and safety of their own homes," he said.

It is an "antigen" test, meaning it works by detecting a surface molecule of the coronavirus, unlike the more common PCR tests that look for the virus' genetic material.

The technology involved is similar to a home pregnancy test.

The Ellume test uses a nasal swab that doesn't go as far back as the nasopharyngeal swabs used in clinical settings, and is therefore more comfortable to self-administer.

The sample is then inserted into a single-use cartridge.

According to the FDA, it correctly identified 96 per cent of positive samples and 100 per cent of negative samples in individuals with symptoms.

In people without symptoms, the test correctly identified 91 per cent of positive samples and 96 per cent of negative samples.

The FDA said that for patients without symptoms, "positive results should be treated as presumptively positive until confirmed by another test as soon as possible."

It added that individuals with positive results should self-isolate and seek additional care from their health care provider, while people who test negative but experience Covid symptoms should also seek follow up with their health care provider.

The home test connects with an app on the user's smartphone to interpret the results.

Results take as little as 20 minutes and are delivered via the app, which requires users to input their zip code and date of birth, to report to public health authorities.

Providing the name and email address is optional.

Ellume developed the test with US$30 million in government funding from the National Institutes of Health.