By Kejal Vyas and Ryan Dube

Three Latin American countries administered their first doses of vaccines against Covid-19 on Thursday, as the region hardest hit by the pandemic begins what health officials say will be a long slog toward inoculating the masses.

Ten thousand Pfizer Inc. vaccines shipped by air from Belgium landed in Costa Rica and Chile as both countries kicked off a vaccination drive that is expected to speed up in early 2021 with the arrival of millions more doses. Mexico began administering 3,000 doses from Pfizer, and Argentina will start inoculations next week after 300,000 doses of Russia's Sputnik V vaccine arrived Thursday from Moscow on an Argentine state aircraft.

The first injections in Mexico and Chile were broadcast live on television.

"It was something unexpected, I'm very excited," said Zulema Riquelme, a 46-year-old Chilean nurse who works with Covid-19 patients and became the first in that country to receive the vaccine. "These have been difficult months because I haven't been able to see my family, a lot of exhaustion. I feel proud that they chose me."

The arrival of the vaccines, which most countries are administering first to front-line health-care workers before giving them to the elderly, offers a glimmer of hope for a region of 650 million that has logged over 470,000 deaths from Covid-19, about 30% of the world's total, and more than 14 million cases. With a new surge of deaths and cases now hammering the region, health officials in most countries are still negotiating purchases with pharmaceutical companies or awaiting delivery of vaccines early next year.

That is raising concerns among health policy experts tracking the pandemic that fully vaccinating the region could lag into 2022 or beyond. Health and government officials said there are limited funds for imports and logistical hardships in distributing vaccines, some of which require ultracold storage that is a challenge in poor, remote regions with intermittent electricity service.

"We need 70%-80% vaccination rates to achieve herd immunity and the way we're going, the coverage is not going to be uniform," said Dr. Carlos Espinal, who leads the Global Health Consortium, a health education initiative at Florida International University. "Without a coordinated effort, the vaccine itself will become a marker of inequity."

While the challenges are similar in much of Africa and Asia, Latin America's needs are particularly pressing because the region has some of the highest daily death rates from Covid-19. Brazil and Mexico, the region's most-populous countries, are each registering nearly 1,000 deaths daily. Fatalities are climbing again in other countries after a lull.

With families across the region ignoring public health warnings to avoid large gatherings and vacations during the holidays, cases are expected to rise even more by early January.

Vaccination is the solution, but most countries lack capacity to produce their own vaccines and must depend on those being manufactured in the developed world, where wealthy countries have made large bulk purchases while moving quickly to administer doses. One million people have already received the shot in the U.S.

Many poor and middle-income countries -- among them a number of countries in Latin America -- are counting on supplies through the Covax multilateral initiative led by the World Health Organization. But it is still unclear when and how many doses will become available.

"We are not Canada or the U.S., with capacity to buy several times our population's size in vaccines," said Fernando Ruiz, Colombia's health minister. "We have much more modest means and have to buy wherever we can."

Colombia has seen its documented daily cases top 14,000 this week, more than the country of 50 million had logged in the last peak in August, when strict quarantine measures were still in place. After signing deals with Pfizer and AstraZeneca PLC in recent days, the government plans to vaccinate nearly 20 million people next year. But that leaves another 15 million who are older than 16 left to inoculate without a clear plan on where those vaccines would come from.

Government officials from Colombia to Chile had been anticipating the results from late-stage trials in Brazil of a Chinese vaccine, hoping that its approval would lead to rapid production in Brazil and exports to neighboring nations. But the announcement on the vaccine's efficacy, which had been expected this past Wednesday, was delayed until January.

Bolivia and Paraguay, two poor, landlocked countries, have yet to sign contracts for vaccines, though health officials in both nations say they are in talks with pharmaceutical companies.

In Peru, which has had one of the world's highest Covid-19 mortality rates, authorities have come under fire because millions of people had been expected to be vaccinated before April's presidential election. But officials this week said they have been unable to close a deal with Pfizer to receive 9.9 million doses.

Former President Martin Vizcarra said that instead of approving purchases, Peru's Congress focused in November on removing him from office in a controversial impeachment. "In all countries they closed contracts to purchase vaccines in November, while here they carried out an illegal impeachment," he said in a tweet.

Carlos Neuhaus, the businessman appointed by the Peruvian government to oversee vaccine distribution, said he faces a range of challenges, including inadequate infrastructure for storing vaccines. He said he has gone so far as to scout supermarkets, fisheries and other companies with large refrigeration facilities.

The Pfizer vaccine, which requires colder refrigeration than other vaccines, "is easier to be applied on the coast, in Lima and the big cities," Mr. Neuhaus said as he discussed Peru's rugged Andean geography. "The other vaccines...should go to the more complicated places."

In Argentina, opposition lawmakers have harshly criticized President Alberto Fernandez for importing the Russian Sputnik V vaccine, which they say needs more testing.

Final results of Sputnik V's trials on patients over 60 haven't yet been released, they said. And 68-year-old Russian President Vladimir Putin, the drug's main promoter, said in his annual news conference earlier this month that he would wait for it to be approved for his age group before getting a shot.

"The national government has improvised since the arrival of the virus to the country, and it is continuing to do so with the vaccines," said Luis Petri, an opposition lawmaker who added that Argentina has been unable to secure supply contracts with multinational pharmaceuticals.

Mr. Fernandez, the president, has said the vaccine is safe and that he would be first in line to take it to shore up confidence. But two dozen lawmakers from the opposition Together for Change coalition want to form a commission to investigate the government's acquisition of Sputnik V vaccines.

"This vaccine doesn't have a guarantee," Elisa Carrio, a prominent former member of congress who is critical of Mr. Fernandez, said in a recent television interview. "This is a great national scam. They are lying to society."

--Silvina Frydlewsky in Buenos Aires and Maolis Castro in Santiago, Chile, contributed to this article.

Write to Kejal Vyas at kejal.vyas@wsj.com and Ryan Dube at ryan.dube@dowjones.com

(END) Dow Jones Newswires

12-25-20 1053ET