The widespread use of rapid antigen tests has taken pressure off testing capacity, but an expert has said they can miss half or more of infected people.
Epidemiologist and University of Auckland professor Rod Jackson said rapid antigen tests (RATs) are useful in slowing down the spread of Omicron but not effective unless performed by trained professionals.
"When performed by untrained people [who] don't swab properly [or] test too soon after exposure, they can perform poorly."
Jackson urged people to read RAT instructions fully and properly.
There are three simple, but detailed, steps to take. Step 1: Take the swab and insert it backwards into a nostril by 2-3cm. Be sure to insert it backwards and not upwards. Then swirl the swab inside the nostril for 15 seconds. Repeat in the other nostril.
Step 2: Put the swab into the vial of solution and rotate it at least five times. While removing the swab, squeeze the sides of the vial to release the liquid.
Step 3: Using the vial, put three drops into the testing well and wait for the time specified per kit instructions. This could be up to 15 minutes.
One coloured line next to the C on the test means a negative result.
Two coloured lines - one next to the C and the T, even faint lines - mean a positive result.
Those who test positive are advised to report their result to My Covid Record or by calling 0800 222 478 and choosing option three.
Last week, the Ministry of Health said it had been receiving reports of symptomatic people testing negative for the virus but later receiving a positive test. Its advice is to stay at home while symptomatic and to retest if symptoms persist or get worse.
"If you are exposed to someone who has tested positive for Covid and then you develop symptoms a few days later, you most likely have Covid-19, even if you have several negative RATs," said Jackson. "You should self-isolate and assume you have Covid."
