As another European winter sets in, some countries are in the midst of a deadly fourth wave of COVID-19 and grappling with fresh outbreaks.
Some nations to reopen have been forced to reintroduce various COVID-19 measures, and others look poised to follow suit.
In Australia, case numbers and deaths due to COVID-19 have decreased and stabilised since the peak of the Delta outbreak, and vaccine rates continue to climb.
But as we reopen to the world, should Australia be bracing for something akin to what's currently happening in Europe?
What's happening in Europe and why?
The World Health Organization says Europe is once again the world's COVID-19 epicentre, with several countries all posting record daily case numbers in recent times.
Around 2.5 million cases and 30,000 deaths have been reported in the past week.
In the Czech Republic, daily cases surpassed 25,000 for the first time on Tuesday. The Netherlands recorded more than 23,700 new infections on the same day, and Hungary reported a record 12,637 cases.
Some countries are also learning a difficult lesson: vaccines work, but they alone won't stop the virus entirely in its tracks.
The United Kingdom, Germany and France are examples of just that.
All three countries have fully vaccinated around two-thirds of their eligible populations - 69 per cent, 68 per cent and 75 per cent respectively, which is slightly higher than the European average of 65 per cent.
But still, experts say these rates are simply too low.
Vaccination rates in the UK, France and Germany are slightly above the European average of 65 per cent. Source: SBS News
"I think these countries, thinking that if they hit 70 per cent level of vaccination can just release all restrictions and everything will be fine, it certainly turned out to not be a successful approach," said University of Newcastle associate professor Nathan Bartlett.
Along with a lagging vaccination rate, there are other key reasons case numbers are surging in Europe.
"One of the issues is that there's been a relaxation of social distancing and mask-wearing, and the third is that its winter, and so people are congregating indoors," said Tony Cunningham, the co-director at Westmead's Centre for Virus Research.
What about booster shots?
Even among the vaccinated, another challenge is arising: waning immunity.
Europe's initial vaccine rollout accelerated quickly in the early months of 2021, which means many residents have now been vaccinated for more than six months.
Jennifer Juno, an immunologist from the Peter Doherty Institute in Melbourne, said this was expected.
"We know now that the effectiveness of the vaccines against actually preventing infection does tend to wane over time, so after that six-month mark, we know people will start to get some what we call 'breakthrough infections' again," Dr Juno said.
This is when it's important for a person to get their booster shot to bolster their immunity to the virus.
About 350,000 booster jabs a day are being administered across the UK. Source: AAP
But many Europeans still aren't able to get booster shots. In France, they're currently only available to people over 50. In the UK, they're reserved for those over 40.
And while all Germans over 18 are now eligible for a booster, that policy only came into effect last week in response to the recent surge in case numbers.
Professor Bartlett said without a uniform approach to boosters by governments, there will continue to be high transmission and hospitalisation rates.
"Their advice around boosters has been very inconsistent," he said.
"This has all meant that boosters have not been rolled out in a comprehensive and effective way, and again this is leaving massive gaps in protection."
Should Australians be concerned?
With the international border re-opening, it's likely COVID-19 case numbers will rise in Australia over the coming months, but authorities say we will be well prepared to deal with it.
Dr Juno said that's because of Australia's high vaccination rate, with 86 per cent of people nationally aged over 16 now having received both doses.
Booster shots will also play a critical role in any potential future outbreaks in Australia. Boosters are available at all participating GPs and pharmacies to everyone over 18 when they become eligible for their shot.
"I think there are a number of factors in our favour at this point in time," Dr Juno said.
"Obviously we have a lot of doses available for our booster doses, so I think that's going to improve our ability to reduce transmission."
But Professor Cunningham said there are still a few caveats.
He said Australia must ensure areas with lower vaccination rates are not left behind, and are given ample opportunity to inoculate as many people as possible.
"We need to look at the places which are not well immunised, and I would suggest that we do need to get them up to 90 per cent to reduce the load of virus circulating in the community, particularly as we open up and more people come in from overseas," he said.
Prof Cunningham also said it would be vital Australia begins to vaccinate children under 12 "before our winter sets in next year."
In addition to a comprehensive vaccine rollout, experts say Australia must continue with its so-called 'vaccine plus' plans to best protect its citizens over the coming months.
Dr Juno said that includes mask-wearing indoors, and high testing and tracing levels.
"All of those types of interventions and activities, and still remembering social distancing, will be very important in helping us get through the next six months."
