Covirus 19 coronavirus: virus circulation in New Zealand is still unknown

While kiwis count hours for life a little weaker than alert level 2, scientists say New Zealand still faces a big question: how much does the virus circulate?

Today, the director general of health, Dr. Ashley Bloomfield, announced another day with no new cases, keeping New Zealand’s count at 1497, of which 94 percent had recovered.

There are now only 74 active cases, and only two people in the hospital, while nearly 6,000 tests were performed yesterday.

Bloomfield said that while the numbers once again showed “we are on the right track,” he emphasized that New Zealand could not afford to give up its profits, a point also emphasized by Prime Minister Jacinda Ardern.

Meanwhile, scientists say it’s unclear how virus transmission has changed as New Zealand dropped from level 4 to level 3 on April 27, and how that could change as restrictions are eased again after tomorrow. when level 2 starts.

Associate Professor Siouxsie Wiles said she would have preferred Level 3 to continue longer to ensure that blocking gains were not wasted.

But the University of Auckland microbiologist was grateful that Level 2 involved a tiered approach in which the size of the meetings would be initially limited.

Dr. Amanda Kvalsvig, an epidemiologist at the University of Otago, explained that the number of contacts people had was one of the main drivers of Covid-19 transmission.

A key baseline was the basic reproductive number of the virus, or “R0,” or the average number of people directly infected by a single infectious individual.

Modeling has suggested that if that number can be kept below one, the virus could be removed.

Kvalsvig noted that level 3 saw a flurry of kiwis expanding their bubbles and returning to public spaces.

“During Level 2, the number of contacts will increase dramatically as people return to work, stores, and public transportation,” he said.

“Covid-19 is highly infectious, so with each step down the level, any virus that is still present will have a much better chance of spreading.”

It was difficult to assess how widely the virus circulated, since people could be infectious but show no symptoms, and we still did not have an accurate management of the proportion of hidden cases.

That was in part due to what scientists call Covid-19’s “lag” or “long tail.”

Although the average incubation period for the virus, or the time from infectious contact to the onset of symptoms, was estimated to be five days, the range was as wide as two to 14 days.

That means that a person who becomes infected today can only show symptoms within two weeks.

However, it was common for people to be infectious before they developed symptoms, so by day 12, that person could unknowingly pass the infection on to another person who could only have symptoms two weeks later.

“It may also take some time to uncover chains of infection among people who do not show strong symptoms,” said Professor Shaun Hendy, director of Te Pūnaha Matatini, who has been modeling Covid-19 in New Zealand.

“Until the disease passes to someone who develops symptoms and is going to be tested, these chains of transmission may persist for some time.”

“Hopefully, these invisible chains have become extinct during level 4, but they may re-emerge once we leave our bubbles and expand our network of contacts.”

Was it possible that rates had quietly risen again after the move to level 3?
Kvalsvig said that due to the great variability in transmission cycles, it was unlikely that there would be an increase overnight when the delay entered.

“But a slow accumulation of cases in the next two weeks would be troubling because it would suggest that a new epidemic curve is developing as a result of the change in physical distance.”

Te Pūnaha Matatini’s modeling suggested that if level 3 had been ineffective, such an increase in cases would emerge in the coming weeks.

It was also possible that New Zealand’s short time spent at level 3, and the relatively small number of cases the country has recorded, may mean that scientists never have a complete idea of ​​how well level 3 worked compared to level 4.

What was important, Kvalsvig said, was that the measures to control Covid-19 remained in place.

At level 4, physical distancing was applying most of that control, but would now switch to other interventions.

“That includes strict border quarantine and active case finding, including looking for asymptomatic cases in high-risk populations, such as nursing homes,” he said.

“It would also be nice to see more evidence of workers who are in contact with large numbers of people, whether through paid work or volunteering. The final barrier is to prevent the virus from being transmitted.”

“That means meticulous attention to handwashing and cough hygiene. Together with my colleagues at the University of Otago, I support the use of face covers on public transport and other crowded and closed places to reduce the risk of virus particles are dispersed in the air by coughing, laughing or just breathing. “

Hendy also highlighted the vital role of contact tracing, an area the government is reinforcing after a review by Otago epidemiologist Dr. Ayesha Verrall exposed several shortcomings.

“While contact tracking apps can help, ultimately it is our human contact trackers that really need to be in your game,” said Hendy.

“We can help them by keeping good records of the places we have been and the people we have met.

“Keep a journal, ask for people’s cell phone numbers when appropriate, and avoid large meetings that will make it difficult to locate contacts.

“With good contact tracking and moderate physical distance, the Te Pūnaha Matatini model suggests that we can keep R0 below 1 while case numbers remain low.”

New models are expected to be released later this week.

• Covid19.govt.nz – The official government Covid-19 advisory website