In hard-hit Brazil, hope unleashed by the first Covid-19 shots is giving way to frustration that the government's vaccination campaign is beset by the same chaos that has marked its pandemic response.
One month after the first dose was administered to a Sao Paulo nurse on January 17 -- setting off a flurry of optimism in the country with the world's second-highest death toll -- Brazil has managed to give shots to about 5.3 million people.
That number accounts for 2.5 percent of the nation's population of 212 million.
Shortages have forced several key areas to halt immunization, including Rio de Janeiro which announced Monday it had to suspend the campaign in the city of 6.7 million until more doses arrived.
"The government made the mistake of putting all its eggs in one basket," said Ethel Maciel, an epidemiologist at the Federal University of Espirito Santo.
Under President Jair Bolsonaro, a far-right social-distancing skeptic who routinely flouts expert advice on containing the new coronavirus, Brazil managed to secure just six million doses for the start of its vaccination campaign.
During the worldwide race last year to gain access to the most promising test vaccines, Bolsonaro bet big on the one developed by British-Swedish pharmaceutical firm AstraZeneca in partnership with Oxford University.
One of the president's top opponents, Sao Paulo Governor Joao Doria, meanwhile struck a deal for his state to purchase and help produce another vaccine, CoronaVac, developed by Chinese firm Sinovac.
That was the vaccine that ultimately got injected into the first Brazilian arm, and it has saved Brazil from having even fewer doses on hand.
"It's a good thing (Sao Paulo) made that deal, because otherwise all we'd have today would be two million doses of the AstraZeneca vaccine, for a population of more than 200 million," Maciel told AFP.
Meanwhile, Bolsonaro "spearheaded an anti-vaccination campaign, saying he wouldn't get vaccinated and warning people it could turn them into alligators," added Maciel, who has submitted a petition for Congress to impeach the president over what she calls his "criminal" handling of Covid-19.
The Sinovac and AstraZeneca vaccines are the only two that Brazilian regulators have approved so far.
The government is counting on delivery of another 100 million doses of the former by the end of August, and 210.4 million doses of the latter by the end of the year.
Both require two doses.
- Racing new variant -
Ironically, the sprawling South American country is known for its turbo-charged vaccination campaigns.
Health workers regularly defy the logistical challenges of reaching the remotest corners of the Amazon rainforest and arid "Sertao," or hinterland, to administer shots.
In 2010, Brazil vaccinated more than 80 million people against H1N1 -- the swine flu virus -- in less than three months.
"The lack of doses has made it impossible for us to do a mass vaccination drive, something we know how to do," said Natalia Pasternak, a microbiologist at the University of Sao Paulo.
But time is of the essence. Brazil, whose Covid-19 death toll is nearing 240,000, is the birthplace of a new, more contagious variant of the virus that emerged in the Amazon and is spreading fast.
"That's why the slow pace of vaccination is so worrying, because the longer we let the virus circulate unhindered, the more mutations may appear," said Pasternak.
Meanwhile, reports have emerged of people with connections cutting in line for vaccination, and of nurses giving fake doses to elderly Brazilians.
The campaign has been marred by a lack of coordination between state, local and federal authorities, exacerbating the chaos.
Despite the difficulties, Health Minister Eduardo Pazuello vowed last week Brazil would vaccinate its entire population by the end of the year.
Experts are skeptical.
"It's possible we'll secure enough doses, but it will be difficult to get them administered by the end of the year," said Guilherme Werneck, an epidemiologist at Rio de Janeiro State University.
"There would have to be a very radical change."