So far, each pandemic wave has been successively worse in Brazil, peaking at a weekly average of around 1,000 deaths per day in July 2020 during the first wave and 3,000 deaths per day last April during the second.

The curve has since turned down, with an average of around 1,600 deaths per day over the past week, and Brazilians have largely gone back to business as usual.

But with the southern hemisphere winter approaching again, experts say warning lights are flashing, raising fears of a return to overflowing hospitals, mass graves, refrigerator trucks piled with corpses and other gruesome scenes from the darkest days of the pandemic in Brazil.

The sprawling country has been slow to vaccinate its 212 million people, and hasty in lifting state and local stay-at-home measures, epidemiologists say.

Meanwhile, risky virus variants — including the “Gamma” strain that emerged in Brazil itself, plus the first cases of the “Delta” strain that emerged in India — threaten to accelerate the disease’s spread.

Covid-19 has already claimed more than 470,000 lives in Brazil, second only to the United States.

The South American country’s per capita death toll — more than 220 per 100,000 inhabitants — is one of the world’s highest.

But many Brazilians seem unconcerned by the threat of a new surge — not least far-right President Jair Bolsonaro, who continues to regularly defy expert advice on containing the virus.

“Brazil has taken an unprecedented health catastrophe and turned it into something normal. The majority of people are acting like there’s no pandemic,” said infectious disease specialist Jose David Urbaez.

“That’s why predictions are for a very intense third surge,” he told AFP.

– Pot-banging protests –
Some experts say a new surge in Brazil should not even be called a “third wave,” given that the first and second never really subsided.

Whatever one calls it, it risks hitting just as Brazil hosts the Copa America, the South American football championships, which Bolsonaro welcomed after organizers pulled the plug on original hosts Argentina at the last minute over their own surge of Covid-19.

The 10-nation tournament kicks off Sunday and will run until July 10.

The mayor of Rio de Janeiro, which is scheduled to host eight matches, including the final, has already said his city may cancel.

With around 10.8 per cent of the population fully vaccinated, the situation in Brazil could get worse before it gets better.

Bolsonaro faces mounting criticism and a Senate inquiry over his controversial handling of Covid-19, including his refusal of various offers of vaccines.

He vowed last week that all Brazilians would be vaccinated by the end of the year, but experts say that will be difficult.

His announcement, made in a nationally televised address, was met by a chorus of banging pots and pans in many Brazilian cities — a traditional mark of protest.

Bolsonaro maintains his refusal to impose lockdown measures is responsible for Brazil’s stronger-than-expected economic growth of 1.2 per cent in the first quarter of the year.

However, experts warn the future of the pandemic recovery in Latin America’s largest economy will depend on how well it contains Covid-19.

Last year, Brazil’s economy contracted by a record 4.1 per cent.

– Mass vaccination: an exit –
“If the speed of vaccination is less than the negative impact of relaxing social distancing measures, the third wave could hit Brazil hard,” said epidemiologist Mauro Sanchez of the University of Brasilia.

One experiment has shown the power of mass vaccination. In the town of Serrana, in Sao Paulo state, public health officials vaccinated 95 per cent of the adult population in a study of the effects of full immunization.

Covid-19 deaths fell by 95 per cent and hospitalizations by 86 per cent in the southeastern town, population 45,000.

“We controlled the pandemic in Serrana. We can do the same across Brazil,” said Sao Paulo Governor Joao Doria, a fierce Bolsonaro critic and leader in the campaign to vaccinate all Brazilians.