Melanie McTighe and her 92-year-old father live in the same city, but they haven't been able to see each other for almost four months.

That changed on Monday as Sydney, Australia's largest city and the capital of New South Wales, emerges from a strict lockdown imposed in June to contain a Delta outbreak.

McTighe said she's "excited" to start her life again and see her loved ones, but she's worried about what having Covid-19 in the community might mean for the city of 5.3 million people.

"I think until everyone has a better understanding of this thing and how it keeps changing, we have to be concerned," she said.

For more than 18 months, Australia has shut itself off from the world, closing borders and imposing strict lockdowns to stamp out Covid-19 outbreaks in an attempt to eliminate the virus.

Now, Australia is emerging from its so-called "cave" and trying to live with it.

From Monday, fully vaccinated Sydneysiders, who make up more than 70% of the city's adults, can return to restaurants, bars and gyms -- and many like McTighe are now able to reunite with loved ones in aged care after months apart.

But all that hard-earned freedom will come at a cost -- national modeling suggests Sydney will see thousands of new infections and inevitable deaths.

Questions remain about how the hospital system will cope with any surge of new cases, the impact on vulnerable people and how quickly Sydney can adapt to living with Covid.

What happens next will be critical for both the city and Australia.

But other zero-Covid countries in the Asia-Pacific region will also be watching closely to see if Sydney can succeed in keeping case numbers and deaths low enough to avoid overwhelming hospitals, while still allowing business to resume and people to get on with their lives.

The end of zero Covid

For the first year of the pandemic, Australia was one of the few major nations to successfully control Covid-19, through strict border restrictions, mandatory quarantine and temporary lockdowns.

But in June a Delta outbreak in Sydney quickly spread to the neighboring state of Victoria and the Australian Capital Territory (ACT).

Delays to Australia's vaccination rollout, partly due to low supplies, left the population vulnerable -- forcing authorities to impose local lockdowns.

"I was always of the belief that we could have eliminated the non-Delta Covid ... but I concede lockdowns with Delta are often going to be an unwinnable contest," said Mary-Louise McLaws, professor of infectious disease epidemiology at University of New South Wales (UNSW).

As case numbers rose, it became clear that keeping people inside was unsustainable -- for economic and health reasons -- and Australian authorities came up with a plan to vaccinate the country out of the pandemic.

With early supply issues resolved, the vaccination program went into overdrive.

Last week, NSW became the first state to reach the initial 70% double vaccination target.

Other states are expected to reach that number in the coming weeks, and by the end of the year the entire country is expected to open up.

But experts warn it's not without potential dangers -- and some people are bearing more of the risk than others.

Reopening Australia

Australia's reopening plan is built around total adult vaccination rates in each state, but inoculation statistics are not evenly spread.

In some suburban areas of Sydney, full vaccination rates are as low as 30%, according to government figures.The state's Indigenous population is also trailing statewide numbers.

For example, as of October 6, fewer than half of Indigenous people aged 15 or over on the NSW Central Coast had received both vaccine doses.

That's a problem because Indigenous people generally suffer more chronic health issues than non-Indigenous people, putting them at greater risk of Covid complications.

And young people are also of concern. In NSW, only 58% of people age 16 to 29 have been fully vaccinated -- the lowest of any age group besides 12 to 15-year-olds, who were only recently given access to vaccines.

McLaws from UNSW said young people are likely to be among the first to take advantage of the freedoms afforded by reopening, so ensuring they are fully vaccinated is especially important.

She compared it to patches of dry kindling which, if ignored, could eventually spark a bushfire.

"Young people, they start the fire, and then those groups that are at risk ... are the vulnerable and the Indigenous population and just generally regional areas outside the big cities," she said.

Australia's strict border controls and quarantine measures allowed the country to avoid the chaos experienced in other countries in 2020, when Covid cases spilled over from hospitals into temporary medical units.

However, despite 18 months of preparation, health groups have warned the NSW hospital system may not be able to cope with a surge of new infections.

Last month the NSW Nurses and Midwives Association urged the state government to boost staffing levels, citing research showing the system was under pressure even before the latest Covid outbreak.

And on Thursday, after NSW's new premier announced a speedier reopening plan, Omar Khorshid, head of the Australian Medical Association, urged authorities not be "reckless".

"The ultimate outcomes of opening too fast or too early will be avoidable deaths and the reintroduction of lockdowns and other restrictions -- things no-one in NSW wants to see," he said in a statement.

"Sydney must take this opportunity to show the rest of the country how to live with COVID whilst protecting health and health care."

Australian Prime Minister Scott Morrison said the country's states have had 18 months to prepare for higher Covid cases -- and the "planning is well in place.

"He also urged Australians to play a role in taking pressure off the system."Where there's no cases, or whether there's 500 cases, or indeed 1,500 cases a day.

The best thing you can do to support nurses and all those working in hospitals is to get vaccinated," he said.

'Setting a 'good example'

Australia is starting its transition from zero Covid to living with the virus through a high vaccination rate -- but it isn't the first country in the region to do so.

In June, the Singaporean government announced it was going to focus on limiting severe Covid-19 cases and lowering hospitalizations rather than infection rates.

Singapore has one of the world's highest vaccination rates -- 83% of its total population is fully inoculated.

But after it began to relax restrictions, Singapore saw Covid-19 cases soar to their highest numbers since the start of the pandemic.

In early October, the country reimposed some restrictions to curb rising infections and take pressure off the health system.

Last week, the number of people allowed to gather dropped from five to two, work-from-home became the standard, and classes were suspended or moved online for students aged 12 and under.

Australia is also expecting case numbers to rise -- that's inevitable as people start mixing, even while following other public health advice, including wearing masks.

National modeling from the Doherty Institute predicts that with "partial public health measures" and a 70% double vaccination rate, numbers could rise to 385,000 cases and 1,457 deaths over six months -- more than Australia's total toll over the entire pandemic.

Greater vigilance could see those numbers drop, it added.

Ahead of the reopening, Australia's leaders have been careful to prepare their citizens for more deaths, casting it as the cost of getting back to normal life.

But like Singapore, Australia has not ruled out reintroducing tighter restrictions if cases rise too quickly.

Apart from Singapore and Australia, New Zealand, Thailand and Vietnam have all spoken about abandoning an elimination strategy.

In some of those places, that has already prompted concern -- in New Zealand, commentators have raised fears the move could spell disaster for the country's most vulnerable.

Experts said countries around the region will be looking to Sydney to see how successfully it moves to reopen -- and to learn from its mistakes.

And not only other countries -- Morrison is keen to move ahead quickly with a nationwide reopening, and Australia's other states and territories will have a close eye on NSW.

Victoria, Australia's second-largest state, will likely be the next to reopen later in October.

Paul Griffin, director of Infectious Diseases at Mater Health Services, said other governments would be particularly interested in how Sydney's health system holds up after reopening.

"I don't think case numbers will be the key metric," he said. "I think it will be markers of significant disease, and intensive care admission and, of course, the death rate.

"If hospitals get overwhelmed by infections, and can't perform normal services safely, that would be a "red flag," he said.

McTighe, the Sydney resident, said she still believes the original lockdown was necessary and doesn't expect the reopening to necessarily be smooth -- there might be a rise in cases and a reintroduction of restrictions, she said.

But for now, she said she is very excited to live "a normal life again."

"You can see a bit of light at the end of the tunnel."