The fast-spreading Omicron variant has made us more reliant on rapid at-home antigen tests to tell us if we have Covid-19. But should we be swabbing our throats as well as our noses?

For now, the guidance depends on where you live.

Some scientists have said people can transmit Omicron when it has infected their throat and saliva but before the virus has reached their noses, so swabbing the nostrils early in the infection will not pick it up.

A small recent US study backed up that view. PCR tests of the saliva from 29 people infected with Omicron detected the virus on average three days before nose samples were positive in antigen, or so-called lateral flow, tests.

In general, rapid tests have a lower sensitivity than lab-processed PCR tests, meaning they produce more false negatives. But if you test positive, you almost certainly have Covid-19, making antigen tests a powerful tool in tackling the pandemic as demand for PCR tests due to Omicron overwhelms laboratories.

As a result of recent studies, some experts in the United States have now advised antigen test users should swab the throat before swabbing the nose.

All the antigen tests with emergency use authorizations from the US Food and Drug Administration use nasal samples and it has expressed concerns over the safety of throat swabbing at home, saying users should follow manufacturers' instructions.

In Israel, a top health official has said people self-testing for Covid-19 should swab their throat as well as their nose when using rapid antigen tests, even if it goes against instructions issued by the manufacturer.

Some other countries, including the United Kingdom, have approved rapid antigen tests that swab both the throat and nose, or just the nose.

In Germany, the minister for health has said they will study how reliable rapid antigen tests are in detecting the Omicron variant and publish a list of the most accurate products.