Health Highlights: Sept. 2, 2020

Here are some of the latest health and medical news developments, compiled by the editors of HealthDay:

Trump Denies Claim He Suffered Mini-Strokes

U.S. President Donald Trump and his doctor are denying a claim that he was treated at Walter Reed Medical Center last fall for mini-strokes.

The president visited the hospital unexpectedly in November, a visit the White House has said was to get a head start on his annual physical.

There haven't been any actual media reports that Trump had suffered a stroke, mini-stroke or heart-related health problem, CBS News noted.

But on Monday, former Clinton administration White House press secretary Joe Lockhart tweeted: "Did @realDonaldTrump have a stroke which he is hiding from the American public?"

Lockhart didn't claim to have any evidence, but said in another tweet on Tuesday: "We are starting to get to the bottom of the ridiculous explanation from the White House that @realDonaldTrump took an unannounced trip to the hospital to do half of his annual physical. It turns out the VP was put on standby to temporarily take over Presidential duties."

On Tuesday, Trump tweeted that the claim was false. "Now they are trying to say that your favorite President, me, went to Walter Reed Medical Center, having suffered a series of mini-strokes. Never happened to THIS candidate - FAKE NEWS," he tweeted.

And Sean Conley, the president's physician, issued a statement later in the day at Trump's request, CBS News reported.

"President Donald J. Trump has asked that I, Dr. Sean Conley, physician to the President, address the recent public comments regarding his health," he said in the statement. "I can confirm that President Trump has not experienced nor been evaluated for a cerebrovascular accident (stroke), transient ischemic attack (mini stroke), or any acute cardiovascular emergencies, as have been incorrectly reported in the media."

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Coronavirus Antibody Levels Remain Stable for Months: Study

A new study shows that levels of antibodies against the new coronavirus remain stable for months in people who've been infected, a promising finding for scientists trying to develop a vaccine against the coronavirus.

Some previous studies have suggested that antibody levels may drop quickly, or that people with few or no symptoms may not make any antibodies, the Associated Press reported.

This study included more than 30,000 people in Iceland. It found that in those who tested positive for the new coronavirus -- ranging from people who were hospitalized for COVID-19 to those without symptoms -- antibody levels increased for two months after infection diagnosis and then leveled off and were stable for four months.

Previous research suggesting that antibody levels drop off quickly mostly checked patients 28 days after diagnosis, the AP reported.

But the authors of the new study said a second wave of antibodies forms a month or two into infection, and this antibody response appears to be more stable and long-lasting.

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U.S. Won't Join International Coronavirus Vaccine Effort

The United States won't join an international effort to create and distribute a COVID-19 vaccine, the Trump administration said Tuesday.

In the announcement, the White House said it doesn't want to be constrained by multi-national groups such as the World Health Organization, the Associated Press reported.

In early July, the Trump administration announced it was pulling out of the WHO.

While some nations have gone it alone to secure supplies of vaccines, others are working together. The COVID-19 Vaccines Global Access Facility (COVAX) is being set up by more than 150 countries and is linked with the WHO, the AP reported.

The Trump administration's decision is shortsighted and will hamper efforts to end the coronavirus pandemic, according to Rep. Ami Bera, D-Calif., a medical doctor.

"Joining COVAX is a simple measure to guarantee U.S. access to a vaccine -- no matter who develops it first," Bera tweeted, the AP reported. "This go-it-alone approach leaves America at risk of not getting a vaccine."

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Uber Riders Will Have to Prove Mask Use

Uber customers who don't wear a face covering during a ride will have to send of selfie of themselves with a mask before they can call Uber again, under a new policy being introduced by the company.

It said the mask verification app will be rolled out in the United States and Canada by the end of the month, and across Latin America and other countries after that, CBS News reported.

The company already permits drivers and riders to cancel trips without penalty if the other person isn't wearing a mask.

In announcing the new policy, Uber cited expert medical advice that wearing a mask can slow the spread of COVID-19, which as caused more than 180,000 deaths in the United States so far, CBS News reported.

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No Proof Convalescent Plasma Effective Against COVID-19: Experts

There's no evidence to support the use of convalescent plasma to treat COVID-19 patients, and doctors should not consider it a standard of care until more research is completed, a U.S. National Institutes of Health expert panel said Tuesday.

"There are insufficient data to recommend either for or against the use of convalescent plasma for the treatment of COVID-19," according to a statement posted on the NIH website by the panel of more than three dozen experts, CNN reported.

"Convalescent plasma should not be considered standard of care for the treatment of patients with COVID-19," said the committee, which evaluates treatments for the new coronavirus.

Convalescent plasma is antibody-laden serum from the blood of people who've recovered from an infection. The theory is that giving this plasma to new COVID-19 patients will boost their immune response, CNN reported.

Last week, the U.S. Food and Drug Administration granted emergency use authorization for the use of convalescent plasma for the treatment of COVID-19.

"Prospective, well-controlled, adequately powered randomized trials are needed to determine whether convalescent plasma is effective and safe for the treatment of COVID-19. Members of the public and health care providers are encouraged to participate in these prospective clinical trials," the expert panel stated.