22 April 2022 | There are 9,390 new community cases of Covid-19 and a further 13 deaths to report today. Video / NZ Herald
An Auckland teenager has tested positive for Covid twice in six weeks - raising questions about official health advice that people probably have good immunity for three months after infection.
The 14-year-old boy first tested positive through PCR in February, as Omicron was beginning to ramp up.
At the time he had just a mild sniffle and a cough, but his sister had Covid and his test soon came back positive as well, his dad told the Herald.
The family isolated for 10 days and the boy returned to school. Then at the start of April "he came home from school really, really quite crook, with a really mean sore throat, fever... the classic symptoms".
The boy's GP suggested it all might have been part of the same infection - that the virus had stayed in his system and was causing belated symptoms. Or he could have caught different variants.
The dad admits he didn't think it was possible to get reinfected so quickly.
"I don't know why we tested him [the second time] because that's what we were led to believe. And the school's policy was once you've had it once then you don't need to worry for the next three months, even if you're a household contact."
He's not sure where his double-vaccinated son caught the virus - neither parent has had it and nobody has come to their house while positive.
The teen has fully recovered and there have been no lasting effects that they're aware of so they're not concerned about long Covid at this stage.
Current Ministry guidelines give a three-month exemption for household contacts after catching Covid, because "the risk of reinfection within the first three months after someone has Omicron is very low".
The 13-year-old's RAT test immediately came back positive, even though he'd had a positive PCR test just six weeks earlier. Photo / Bevan Conley
The dad was curious whether the Government was reconsidering its advice that people are unlikely to catch Covid again within three months of infection.
"Clearly you can get it twice. I'm sure he's not the only one."
The 14-year-old's infections were both logged on his My Covid Record.
But according to a Ministry of Health spokeswoman, the ministry is not collating reinfection data.
Reinfections had occurred during Omicron outbreaks overseas but they were usually due to catching Omicron after getting a previous variant like Delta or Alpha, she said.
"Omicron reinfections are uncommon, although it has been shown to occur."
Most reinfection cases were easy to spot because there was a long period between recovery from the first infection and the second.
"However, some people have symptoms for weeks or even months and it is difficult to know if they are due to the old infection or a new infection."
Reinfection within three months was also uncommon, especially in New Zealand where there was a low rate of infection pre-Omicron, she said.
However, "reinfection in New Zealand is likely to become more common as time goes on, which reinforces the importance of vaccination, including boosters, as our best defence against Covid-19".
The Ministry of Health advises people do not need to repeat a RAT again for 28 days after they test positive.
"The result may continue to be positive, but this doesn't necessarily mean that you're still infectious."
But if someone had new symptoms a month or more after testing positive they should do another RAT, the advice says.
Will New Zealand see a second wave of Omicron infections?
Many countries are now being hit with second waves – and for a clear reason, Herald science reporter Jamie Morton wrote in March.
When Omicron began washing over the globe, it was travelling in the form of its original type, BA.1.
Since then, we've seen the rise to global dominance of the faster-spreading BA.2 type, which has caused case rates to soar again in countries that were hit by Omicron earlier.
The subtype shares the same 32 mutations with BA.1 - but many others that set it apart.
"We might talk about BA.1 and BA.2 as both Omicron, but actually, they're quite genetically distinct – and we may even think of them as different variants," University of Otago virologist Dr Jemma Geoghegan said.
"That's meant that places that only experienced BA.1 are seeing cases increase again."
The good news was that being infected with BA.1 still appeared to provide good cross-protection against BA.2 - and that reinfection with one after the other was uncommon.
In a Danish study that examined more than 1.8 million cases over three months, there were fewer than 50 instances in which people contracted BA.2 after having had BA.1.
A similar trend was observed among more than 500,000 sequenced cases in the UK, of which just 43 possible cases of BA.2 reinfection were discovered.
In another positive, boosters worked similarly against both sub-types – and on an individual basis, BA.2 infections didn't necessarily make people sicker.
Because New Zealand has effectively been experiencing two Omicron waves at once – BA.1 and BA.2 - Geoghegan thought it unlikely we'd see that same BA.2-powered second surge other countries are experiencing.
If we did happen to suffer another Omicron wave later this year, it might simply be because our immunity against either type has waned.
"Essentially, once you've been infected, it's thought that you're protected against reinfection, certainly with the same variant, for a good three months," said University of Auckland immunologist Associate Professor Nikki Moreland.
