SINGAPORE – Demand for antigen rapid test (ART) kits has surged in recent weeks as the number of Covid-19 cases in Singapore hit a record high for 2023.
Checks by The Straits Times on Dec 6 found several pharmacies and stores had run out of ART kits, and shelves remained bare the day after.
On Dec 11, the Ministry of Health (MOH) said retailers and pharmacies have sufficient supply and have placed fresh orders to meet the spike in demand.
The Straits Times spoke to experts to find out whether people can continue to safely use ART kits and masks even if they have expired, and whether the kits will still be effective when testing for the latest Covid-19 variants.
Q: What is the shelf life of ART kits and masks?
A: The United States Food and Drug Administration (FDA), which approves ART kits, has said the shelf life of these kits is between four and six months from the date of manufacture.
However, shelf life can be longer than the given expiry date found on the packaging if the manufacturer finds that test results are more stable. In that case, manufacturers can ask FDA to give test kits a longer shelf life.
To check if the expiry date of an ART kit has been extended, go to this website.
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Unlike ART kits, the shelf life of masks, and likelihood of extending their expiry dates, is unclear, said Professor Paul Tambyah, an expert in infectious diseases at the National University of Singapore (NUS) Yong Loo Lin School of Medicine.
He said: “Unfortunately, there are so many mask manufacturers that there is no equivalent of the FDA website listing on extended expiry dates for masks.”
Prof Tambyah said people can refer to the expiry dates found on the mask packaging as well as the instructions on how best to store them.
Q: Can I still use expired ART kits and masks?
A: No, expired ART kits can give inaccurate results, while expired masks provide less protection against Covid-19, said health experts.
Prof Tambyah said misleading results like false positives and false negatives can arise from the degradation of chemicals in the test solutions.
ART tests work by identifying the viral antigen – usually the nucleocapsid (N) protein of Sars-CoV-2, which is the virus that causes Covid-19. The antigens bind to antibodies, resulting in a line on a test strip.
If the antibodies have degraded, the test kit may not be able to detect the viral proteins, or may indicate a false positive even if the protein is not there, added Prof Tambyah.
As for expired masks, the fabric is likely to degrade over time, forming micro tears invisible to the eye, said Associate Professor Richard Sugrue, who specialises in molecular and cellular virology at the Nanyang Technological University School of Biological Sciences.
He said: “If someone with Covid-19 coughs out droplets of saliva towards you, the droplets would land on the surface of your mask and it is unlikely you will inhale it.
“But, if there are tears in your mask, the droplets can get in and infect you.”
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Q: Can I still use my test kit if it is past its expiration date by one day to a week?
A: Health experts said it is best to avoid using expired ART kits as it is hard to predict how the tests will turn out.
Prof Tambyah said: “Bear in mind that most of the testing has been done in conditions where the room temperature is about 18 deg C to 22 deg C in temperate countries, not in hot and humid Singapore.”
However, Prof Sugrue said a test kit narrowly past its expiry date could still be able to provide accurate results.
He said: “A test kit past its expiry by one day to two weeks should be okay, but a kit past its expiry by six months to a year would be more of an issue.”
A negative test result using an expired kit should be viewed with caution, and symptoms will need to be monitored carefully as a precaution, he added.
Q: Can ART kits pick up on the latest Covid-19 variants?
A: Yes, most ART kits can pick up on new Covid-19 variants, said Prof Tambyah.
He added that most ART kits do not target the spike protein, where most of the virus mutations have occurred. Instead, they target the N protein, which has stayed constant throughout the pandemic.
Data published on the MOH website showed that up to Dec 8, cases infected by JN.1, a sublineage of BA.2.86, accounted for more than 60 per cent of Covid-19 cases in Singapore.
Other main variants that are spreading globally include the Omicron sub-variant XBB.1.5 and EG.5 (Eris) variants.
Prof Tambyah said: “There is no evidence that the test kits are missing more cases of Covid-19 now than they missed a couple of years ago, when they were first introduced.”
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Q: What can I do with my expired ART kits and masks?
A: Prof Tambyah said people can consider donating to charity clinics kits that will be expiring soon.
Mechanical engineering professor Seeram Ramakrishna from the NUS College of Design and Engineering said the plastics, paper and cardboard in an ART kit can be recycled.
Unused kits can also be recycled after the chemicals have been removed and the materials are thoroughly washed, he added.
Expired masks can also be used to make lifestyle accessories like hair ties, kitchen and gardening aids, and miniature furniture for pets.
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