Health Highlights: March 19, 2021

U.S. to 'Loan' COVID-19 Vaccines to Mexico, Canada

A "loan" of 4 million doses of the AstraZeneca COVID-19 vaccine will be sent to Mexico (2.5 million doses) and Canada (1.5 million doses), the White House said Thursday.

"Our first priority remains vaccinating the U.S. population," White House Press Secretary Jen Psaki said at Thursday's daily briefing. But she added that "ensuring our neighbors can contain the virus is a mission critical step," the Associated Press reported.

The plan's details are still being worked out.

The AstraZeneca vaccine has not been approved for use in the United States, but the company is expected to share results of its late-stage U.S. study and apply for emergency use authorization in the coming weeks. The World Health Organization, European regulators and dozens of countries have OK'd the shots based on studies done in the U.K. and elsewhere.

Over the past week, several nations suspended their use of the vaccine following reports of clots in a few dozen of the millions of people across Europe who have received the vaccine. On Thursday, Europe's medicines regulator said the shots do not increase the overall risk of clots and the benefits far outweigh the risks. Still, the debate raised fears that the safety question would undermine confidence in AstraZeneca's vaccine, which is key to immunization efforts in several countries.

The Biden administration has said that once U.S. citizens are vaccinated, the next step is ensuring Canada and Mexico can contain the pandemic so the borders between those countries can reopen.

'Perfect Storm' Triggered COVID-19 Pandemic: Researchers

It took a "perfect storm" for the COVID-19 pandemic to occur, according to researchers who examined when and how the virus first emerged in China.

They found that the new coronavirus didn't infect the first human until October 2019 at the earliest, and that it was bad luck and the crowded setting of the Huanan seafood market in Wuhan -- where the pandemic appears to have started -- that set the virus on its worldwide spread, CNN reported.

The study was published Thursday in the journal Science.

"It was a perfect storm -- we know now that it had to catch a lucky break or two to actually firmly become established," study co-author Michael Worobey, a professor of evolutionary biology at the University of Arizona, told CNN.

"If things had been just a tiny bit different, if that first person who brought that into the Huanan market had decided to not go that day, or even was too ill to go and just stayed at home, that or other early super-spreading events might not have occurred. We may never have even known about it."

The research team used molecular dating, which involves assessing the rate of ongoing mutations to calculate how long the virus has been around. They also ran computer models to show when and how it could have spread, and how it did spread.

"Our study was designed to answer the question of how long could SARS-CoV-2 have circulated in China before it was discovered," said researcher Joel Wertheim, an associate professor in the San Diego School of Medicine's Division of Infectious Diseases and Global Public Health.

"To answer this question, we combined three important pieces of information: a detailed understanding of how SARS-CoV-2 spread in Wuhan before the lockdown, the genetic diversity of the virus in China, and reports of the earliest cases of COVID-19 in China. By combining these disparate lines of evidence, we were able to put an upper limit of mid-October 2019 for when SARS-CoV-2 started circulating in Hubei province."

Top-Selling Flea Collar May Be Linked to Nearly 1,700 Pet Deaths

A top-selling flea collar that may be linked to the deaths of nearly 1,700 pets and hundreds of injuries to people should be recalled, a U.S. lawmaker says.

Since the Seresto collars were introduced in 2012, there have been more than 75,000 incidents -- ranging from skin irritation to seizures to death -- reported to the U.S. Environmental Protection Agency, according to government documents obtained by a nonprofit group, CBS News reported.

Congressman Raja Krishnamoorthi wants a recall of the collars, which contain two different pesticides to combat fleas and ticks.

"I think that it's only appropriate in this case that the manufacturer do a voluntary recall," he said, CBS News reported. "We look at the situation, investigate and then proceed from there."

Retailer Elanco says the collars are safe. The "incident report rate … in the U.S. has been below 0.3%" and the majority "relate to non-serious effects" such as skin problems, according to the company.

Elanco says it will not issue a recall. That's something that would be up to regulators, a company spokesperson told CBS News.