While Covid-19 reinfections aren’t common, experts warn they may be missed if people follow the Government’s advice not to test for 90 days after an original positive test result.
Newsroom reported on Wednesday morning that the Ministry of Health was overruling that guidance, but a further clarification from the ministry says the advice still stands.
“The Ministry does not currently advise self-retesting within 90 days of Covid-19 infection and it was incorrect to say so in a statement to Newsroom,” a spokesperson said. The mistake happened as a result of “internal miscommunication”. The spokesperson said the advice is being reviewed but that any change “will be provided by the ministry to both health professionals and the public”.
For months, the Government has advised anyone who has recently had Covid-19 not to take a test if symptoms return within three months.
“If you are at low risk of severe illness, stay home and recover until 24 hours after you no longer have symptoms. You do not need to take a rapid antigen test (RAT),” the covid19.govt.nz website recommends. Vulnerable people are instructed to contact their doctor or Healthline.
Anne Wyllie, a microbiologist and testing expert at the Yale School of Public Health, calls that guidance “dangerous misinformation”.
Covid-19 reinfections shortly after an initial infection are rare, but a positive rapid test is more likely to signify reinfection than to be a false positive.
“Antigen tests only detect infectious levels of virus, they do not detect historic infections like some PCR tests can do. Antigen tests are the best way of determining whether you are a risk to those around you,” Wyllie said.
“If you have symptoms and test positive on a RAT [within 90 days of testing positive], this would be reinfection and while you continue to test positive, you continue to be a risk of passing infection onto others.”
“Hopefully, the protection from infection will actually last longer, at least a couple of months, but it is important not to think you’re completely safe, for very long.”
– Anne Wyllie, Yale School of Publish Health
If reinfected Covid-19 cases don’t test, they won’t know they have the virus. If they leave isolation once their symptoms resolve, they could still be infectious. The case’s household contacts also wouldn’t be required to isolate or test.
Wyllie said reinfections have been reported as recently as three weeks after the initial infection. These are usually confirmed by genomic sequencing which shows that two different variants of the virus were involved in the separate infections.
“Hopefully, the protection from infection will actually last longer, at least a couple of months, but it is important not to think you’re completely safe, for very long,” she said.
This is further complicated by the arrival of new Omicron subvariants in New Zealand, which are better at infecting those who have immunity from one of the original two subvariants.
“It’s a general principle, the greater the genetic difference between two variants, the higher the risk of reinfection,” Ayesha Verrall, a former epidemiologist and the current Associate Minister of Health, told Newsroom.
University of Otago evolutionary virologist Jemma Geoghegan said there was limited data around reinfections in New Zealand because so few people test with PCR. Rapid test results can’t be sequenced and it would be “almost impossible” that the same person would be sampled twice by PCR. Only a few hundred cases each week are sent for sequencing these days, out of more than 40,000.
Verrall said the ministry was having a second look at the advice not to test within 90 days of a positive test result.
In the mistaken statement that arose from “internal miscommunication”, a spokesperson for the ministry had told Newsroom on Tuesday that people should test if they developed symptoms, even if they recently had Covid-19. However, the spokesperson didn’t acknowledge this was a change in policy.
“Anyone who has symptoms within 90 days of having Covid-19 should still get a test and follow public health guidance,” the spokesperson said at the time.
That withdrawn statement continued: “It is very unlikely for a RAT to remain positive for more than 14 days after infection. If a person develops new symptoms consistent with Covid-19 within 28 days it is very unlikely that they have a reinfection.
“If a person develops new symptoms consistent with Covid-19 between 29 and 90 days, it is possible they have a new Covid-19 infection, particularly if they have a positive RAT. However, it’s important to note that each individual’s situation will be different.”
The ministry is updating its contact tracing database to better track the number of reinfections in health workers.