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Members of the National Guard march during the announcement of the new measures by the Mexican government to deter illegal crossings at the southern border with Guatemala, in Tuxtla Gutierrez, Mexico, on March 19, 2021.JACOB GARCIA/Reuters

An hour after Mexico announced pandemic travel restrictions in closing its northern and southern borders last week, the Foreign Ministry announced a deal that would secure 2.7 million vaccines from the United States.

And barely 24 hours later, Mexico’s National Immigration Institute deployed agents to the southern border to protect child migrants, and police, national guard members and immigration agents marched in a show of force through the streets of Tuxtla Gutierrez, capital of the border state of Chiapas.

Mexican officials described the events as coincidental, with government spokesman Jesus Ramirez Cuevas calling the sharing of vaccines “a gesture of solidarity.” White House spokeswoman Jen Psaki also called the delivery of vaccines and beefed-up immigration enforcement “unrelated.”

“There are those who ask me, ‘Well, in exchange for what?’ because every time there is an agreement with the United States or another country, it’s always the same question,” Mexican Foreign Minister Marcelo Ebrard said Friday.

Tracking Canada’s COVID-19 vaccine rollout plans: A continuing guide

Moderna, Pfizer, AstraZeneca or Johnson & Johnson: Which COVID-19 vaccine will I get in Canada?

Canada pre-purchased millions of doses of seven different vaccine types, and Health Canada has approved four so far for the various provincial and territorial rollouts. All the drugs are fully effective in preventing serious illness and death, though some may do more than others to stop any symptomatic illness at all (which is where the efficacy rates cited below come in).

PFIZER-BIONTECH

  • Also known as: Comirnaty
  • Approved on: Dec. 9, 2020
  • Efficacy rate: 95 per cent with both doses in patients 16 and older, and 100 per cent in 12- to 15-year-olds
  • Traits: Must be stored at -70 C, requiring specialized ultracold freezers. It is a new type of mRNA-based vaccine that gives the body a sample of the virus’s DNA to teach immune systems how to fight it. Health Canada has authorized it for use in people as young as 12.

MODERNA

  • Also known as: SpikeVax
  • Approved on: Dec. 23, 2020
  • Efficacy rate: 94 per cent with both doses in patients 18 and older, and 100 per cent in 12- to 17-year-olds
  • Traits: Like Pfizer’s vaccine, this one is mRNA-based, but it can be stored at -20 C. It’s approved for use in Canada for ages 12 and up.

OXFORD-ASTRAZENECA

  • Also known as: Vaxzevria
  • Approved on: Feb. 26, 2021
  • Efficacy rate: 62 per cent two weeks after the second dose
  • Traits: This comes in two versions approved for Canadian use, the kind made in Europe and the same drug made by a different process in India (where it is called Covishield). The National Advisory Committee on Immunization’s latest guidance is that its okay for people 30 and older to get it if they can’t or don’t want to wait for an mRNA vaccine, but to guard against the risk of a rare blood-clotting disorder, all provinces have stopped giving first doses of AstraZeneca.

JOHNSON & JOHNSON

  • Also known as: Janssen
  • Approved on: March 5, 2021
  • Efficacy rate: 66 per cent two weeks after the single dose
  • Traits: Unlike the other vaccines, this one comes in a single injection. NACI says it should be offered to Canadians 30 and older, but Health Canada paused distribution of the drug for now as it investigates inspection concerns at a Maryland facility where the active ingredient was made.

How many vaccine doses do I get?

All vaccines except Johnson & Johnson’s require two doses, though even for double-dose drugs, research suggests the first shots may give fairly strong protection. This has led health agencies to focus on getting first shots to as many people as possible, then delaying boosters by up to four months. To see how many doses your province or territory has administered so far, check our vaccine tracker for the latest numbers.

Coronavirus tracker: How many COVID-19 cases are there in Canada and worldwide? The latest maps and charts

“It has another message, which, I think is very positive, is the rebirth or the recuperation of the North American region for confronting common problems. So that relationship is going to be constructed.”

But the timing of the vaccine deal raised eyebrows in Mexico, where the COVID-19 vaccination campaign has sputtered despite government assurances enough vaccines have been acquired.

Mexico sending security forces to its southern border, meanwhile, repeats an old pattern of the country responding to U.S. pressure or incentives to slow the stream of Central American migrants transiting Mexican territory toward the United States.

“The top card that Mexico has to play in the bilateral relationship at this point is migration control,” said Brenda Estefan, a former security attache at the Mexican embassy in Washington.

“The Biden administration knows what the Mexican government did to ‘help’ curb an influx of Central American migrants in 2019,” she said, referring to the country’s response after then-president Donald Trump threatened escalating tariffs on Mexican imports unless migration was stopped. “They know it works. They know they can ask for it. And they know Mexico is desperate to have more [vaccine] doses.”

The deal comes as large numbers of families and unaccompanied minors arrive at the U.S.-Mexico border. It’s created a conundrum for the Biden administration, which has wanted to put a friendlier face on U.S. immigration policy without sparking a surge in migration. The number of migrants trying to enter the U.S. has increased since April, 2020, with 100,441 detainees reported last month by U.S. border officials, the highest level since March, 2019.

But it’s proving impossible as migrants see hope in an administration undoing the restrictive policies imposed under Mr. Trump and flee desperate situations in Central America, including twin hurricanes battering the region in November. Observers say a new Mexican law forbidding the detention of child migrants has also eased the arrival of so many minors at the U.S. border – and prevents the return of some child migrants to Mexico. Mexico’s immigration institute also alleged smugglers are using children as a means of “safe passage … to facilitate entry into Mexico and the United States.”

“There was a change of government in the United States with Joe Biden so they’re hopeful, almost all of them, of arriving in the United States. They also think the border is going to be easy to cross,” said Franciscan Father Gabriel Romero, director of the migrant shelter La 72 in southern Tabasco state near the border with Guatemala.

“[Smugglers] are giving them the message that with the Biden government their chances of remaining in the United States are better,” said Juan Jose Hurtado, director of the Guatemalan community organization Pop No’j, which works with migrant families.

“But it’s also because the causes forcing migration are not continuing, but worsening. People are frustrated and don’t see much hope with corrupt governments not serving citizens’ needs.”

Mr. Biden has promised to pump US$4-billion into developing Central America and promoting better governance in the region to stem the flow of migration.

But he’s also resorting to an old tactic employed by his predecessors: outsourcing migration enforcement to Mexico and pushing the U.S. border further south.

“Their migration system is broken and until they get a migration reform, they need Mexico. The only other option is to militarize the border,” Ms. Estefan said.

“It’s only natural that they turn to Mexico and tell them, ‘We have 2.5 million vaccines for you.’ ”

Mexico has vaccinated roughly 5 per cent of its population as of Sunday. And the process has proceeded slowly and haphazardly, with long lines of seniors forming in the predawn hours at vaccination centres around the country.

The vaccination strategy has also been called into question, though President Andres Manuel Lopez Obrador insists enough vaccines will be available.

Mexico has taken vaccinations to some of its poorest and most remote municipalities – part of the President’s professed preference for putting “the poor first.”

But health analysts question the wisdom of vaccinating rural regions ahead of densely populated urban areas. They also criticized the recent vaccination of Mexico’s Olympic athletes, when more than 20,000 health care workers (mostly in the private sector) remain unvaccinated.

“Mexico was one of the first countries in Latin America to have vaccines,” said Roselyn Lemus-Martin, a Mexican COVID-19 researcher. But other countries have in the region have vaccinated more quickly than Mexico.

“It’s a combination of politics, they didn’t know what they were doing, they went too slow and once it was time, many countries were ahead of them,” she said.

The COVID-19 pandemic has hit Mexico hard – with both Mr. Lopez Obrador and coronavirus czar Hugo Lopez-Gatell recently contracting COVID-19. Its response of pushing fiscal austerity, applying few tests and wavering on recommending mask use has also been questioned.

Mexico has not imposed any travel restrictions on flights from countries with severe COVID-19 outbreaks and has not required COVID-19 tests to enter the country.

Like Canada, Mexico has faced the frustration of supply-chain difficulties and waiting for vaccine orders, prompting it to strike deals with Russia and China.

“What we’ve done with vaccinations is the exact same thing we’ve done with the pandemic: save money,” said Xavier Tello, a non-practising physician and health-care analyst in Mexico City.

“I would like to be in Canada’s position because Canada has already paid and is expecting delivery. … Mexico is [still] negotiating and buying.”

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