There was a collective gasp as Victoria’s daily case count jumped by more than 50% in a day to hit 1,438 on Thursday. Before that, we were tracking below the Burnet Institute forecasts and the reproductive number had been trending back down towards one. Our infection rates were slowing.
Case numbers do move around day on day and we tend to see our highest daily rates between Thursdays and Saturdays. For this reason, we often use rolling averages rather than single-day figures when examining the trends. While that smooths the reported cases, the three-day average still went from 887 to 1,085 and, if the numbers stay around this mark for the next few days, this will push the reproduction number up further, with it now sitting around 1.4. For Delta, this translates to a 40% increase in cases every four days or so. This we do not want.
Previously, when we have seen the reproduction number rise, it has held for four to five days then declined again. Our most notable jumps in case rates previously occurred about 12 days after protests were held, just as this one has.
It is not just the risk of transmission at these events that is a public health concern but the possibility that people will refrain from testing even if symptomatic. A couple of generations of transmission later and new cases have no idea they have any link to the protest and find themselves with symptoms and get tested. It is difficult to prove an association with the protests but with Delta we have seen the same pattern after every Melbourne protest.
The contact tracers have also reported that many of the new cases were linked to household gatherings over the AFL grand final weekend. This is a risk in its own right given the wide geographic spread of viral transmission and homes being the highest risk transmission setting. But it is also possible that these gatherings might have put a fan to spot fires seeded by protesters who did not know they had become infectious.
It is equally true that after each rapid rise in cases we have been able to bring the reproductive number back down towards one. It is also true that our background vaccination rates are higher week on week and we are now at the levels Sydney was when they started to see their case numbers plateau, and then, a couple of weeks later, fall.
Vaccination cover, even just a few weeks after the first dose, makes a difference. One dose reduces the chance of becoming infected and of having serious illness if infected. It’s not as good as being fully vaccinated but you are only two-thirds as likely to become infected as an unvaccinated person, and two-thirds less likely to end up in hospital if you are infected.
It also matters where the vaccine coverage is. High overall rates are good but if the virus is spreading in parts of the community that have lower than average rates then we still have a problem trying to control transmission. And here lies the most encouraging news. Vaccine rates have been on the rise across Victoria, especially those having their first doses. And the best news? The uplift is highest in those areas with the greatest community transmission.
Just four weeks ago, only 41% of people over 15 in Hume had received their first dose. Now it is 74%, climbing by more than 9% each of the last two weeks. Wyndham is also impressive, averaging climbs of more than 8% each week, and Whittlesea also climbed more than 8% last week.
Victoria may now struggle to stay under the case numbers that Burnet modellers have predicted along the roadmap but our hospitalisations are still less than forecast.
Severe illness is in fact the limiter on this path out of Covid-zero. Accelerate the vaccine rollout, especially in the areas where the virus circulates, and you can beat the model. We saw this in Sydney, with hospitalisations peaking and beginning to drop within two weeks of cases peaking. The ICU admissions usually peak later given the length of stay but they are already starting to decline in New South Wales.
The other important control measure in these Delta outbreaks is trying to keep the outbreak focused in contained areas where the public health response can then also be concentrated. This has been more difficult in Victoria, with multiple hotspots emerging quickly, and now new suburbs being caught up in the outbreak.
The best way to respond is to accelerate the vaccination program across the entire state, and we now have the supply to do this with a further 18,000 doses of Moderna landing in Victoria on Monday. Our October doses are now also secured, so we will soon reduce the Pfizer dose spacing back down to three weeks, bringing forward meeting those all-important double-dose targets that are tied to coming out of lockdown.
If all local government areas can lift their first-dose coverage by 10% for a few weeks, then we get out of this faster and save more lives in the process.
I for one would prefer to wake to the news of the LGAs with the highest vaccination rates this week rather than increasing hospitalisation rates. We all are waiting for the day when case numbers should no longer be the main focus; in fact I’d argue we are already there.
If we can protect our hospitals by containing transmission and reducing illness among those infected then high vaccination rates can still push us along the Victorian roadmap.
Catherine Bennett is chair of epidemiology at Deakin University
