Vaccine rollout stops Sydney Covid outbreak numbers from soaring, say experts

Sydney’s growth of new infections is running at a little more than half of that experienced by Melbourne last year at the same stage despite NSW grappling with a more infectious strain.

Gladys Berejiklian (left) and Victorian Premier Daniel Andrews (right).

Sydney’s growth of new Covid-19 infections is running at a little more than half of that experienced by Melbourne last year at the same stage of its outbreak despite the fact NSW is grappling with a more infectious strain.

Victoria’s seven-day average of new Covid-19 cases stood at 10.1 on June 17 last year. By July 19 last year the seven day average of new Covid-19 infections had ballooned to 287.1.

Over the same 33-day period Sydney’s seven-day average of new cases has risen from 12.6 on June 26, when a lockdown was imposed on four Sydney local government areas, to 151.7 on Wednesday when Gladys Berejiklian extended Greater Sydney’s lockdown for 28 days.

Over the same comparable period 19 people had died in Victoria compared with 11 in Sydney.

The rate of growth in the two outbreaks was broadly similar for the first three weeks. Victoria’s seven-day moving average passed 100 on day 21 (102.3 on July 7, last year). While Sydney’s seven-day average of new cases jumped into the nineties on day 22 (96 on July 17) and stayed in the nineties until day 27, July 22.

Once Melbourne’s seven-day average had passed 100 it doubled over the next six days.

Sydney’s seven-day moving average has gone up by about 50 per cent in the six days since it passed a seven-day average of new cases of 100 – from 105 on July 22 to 151 on Wednesday.

Australian National University infectious diseases expert Peter Collignon said it was “good news that the trajectory of cases in Sydney is less steep than Melbourne, especially given the Delta strain Sydney is dealing with is twice as infectious”.

“Also, I think the consequences of the outbreak in terms of death should be less than in Melbourne because of the rollout of the vaccine, particularly to higher-risk groups,” Professor Collignon said.

“Most people in aged care have been vaccinated, as have many people over 70. This is why you are seeing a disproportionate number of younger people in hospital with Covid.”

Infectious diseases expert Sanjaya Senanayake said the most significant difference between the two outbreaks, beyond the strain, was the fact NSW had not let the disease permeate into the hospital and aged-care systems.

“In Victoria hospital-acquired Covid was a significant issue last year,” Associate Professor Senanayake said.

“The fact these workers, aged-care residents and many nursing home workers are vaccinated has definitely helped with lower deaths from Covid, and likely helped with overall transmission.”

Melbourne University epidemiologist Tony Blakely said it was difficult to compare the two outbreaks as the Delta virus was so different from what Melbourne dealt with in 2020, but lessons could be learned nevertheless.

Epidemiologist Tony Blakely. Picture: Alex Coppel

“There was so much we know now we didn’t then. Contact tracing wasn’t as good, masks were not considered as important, aerosol transmission was downplayed,” Professor Blakely said.

“It’s clear NSW didn’t lock down early enough, and the numbers quickly escalated to the point they were too high for contact tracers do deal with. Contact tracing is a different matter this time, given the time interval from becoming infected to being able to infect others is now around 24 hours.

“Previously, contact tracers had this wonderful period of grace of up to 72 hours to get contacts of an infected person into isolation. That has gone.”

Professor Blakely said essential workers in non-health settings in NSW had replaced health workers as a potential source of the spread.

Associate Professor Senanayake said there should be a big push by the NSW government to prioritise the vaccination of essential workers, which could begin to help stifling the further spread of Covid, potentially within a month or two.

Victoria’s second wave last year emerged on May 27. The outbreak topped out at a seven-day average of 512 on August 5. Overall, 802 people died, 655 of them in nursing homes.