What you need to know about coronavirus on Monday, October 12

Tens of thousands of people have signed up to take an experimental vaccine candidate and then face the coronavirus in a controlled setting, Mick Krever, Phil Black and Cristiana Moisescu report.

"The risk to me is tiny. But by taking that small risk on myself, I can potentially protect thousands of other people from having to be infected without consenting to it," said 18-year-old Alastair Fraser-Urquhart, one of those who signed up.

Human challenge trials are nothing new. They have been used for cholera, typhoid, malaria, and even the common cold. But unlike for those diseases, there's no completely effective treatment for Covid-19, should the experimental vaccine fail.

The UK government said that it is in active conversations to collaborate on such a trial, which would be the first in the world for Covid-19. Already, several big vaccine developers -- among them AstraZeneca, Sanofi and BioNTech -- have said that they have no interest in participating.

More than 100 top scientists including 15 Nobel laureates wrote an open letter in July, calling for volunteers to be exposed to the coronavirus to assist with vaccine development.

YOU ASKED. WE ANSWERED

Q. Do you need a negative coronavirus test to leave isolation?

A: Donald Trump's doctor said Saturday that the President had met criteria from the CDC to leave isolation after falling sick with the coronavirus. The White House didn't say Trump had actually tested negative for the virus -- but according to CDC guidelines, people don't generally need a negative test to be around people again.

According to the CDC, research has shown that people aren't likely to be infectious 10 to 20 days after symptoms first began, regardless of test results.

Send your questions here. Are you a health care worker fighting Covid-19? Message us on WhatsApp about the challenges you're facing: +1 347-322-0415.

WHAT'S IMPORTANT TODAY

Trump returns to campaign trail claiming he's immune

The President resumed public activities over the weekend, nine days after announcing he tested positive for the coronavirus. Trump plans to hold a rally in Florida tonight -- his first since his positive diagnosis. His physician has cleared his return.

Yesterday Trump tweeted that he was now immune to Covid-19, but there is no evidence that people are immune to Covid-19 if they have been infected once, according to the CDC. In fact, the CDC specifically cautions people not to assume they are immune. Twitter has added a warning label to the tweet.

As Trump returns to the campaign trail, a new election ad features Dr. Anthony Fauci appearing to praise the President's handling of the pandemic. Fauci, however, told CNN his words were taken out of context and used without permission.

Chinese city will test 9 million residents after hospital cluster emerges

Everyone in Qingdao will be tested for the coronavirus over the next five days following an outbreak linked to a hospital treating imported infection. The city reported nine Covid-19 infections on Monday.

China, whose official reported virus numbers have stayed low since the spring, was the only major world power to avoid a recession this year. The country built its relatively quick recovery through several measures, including stringent lockdown and population tracking policies. The government also set aside hundreds of billions of dollars for major infrastructure projects, and offered cash incentives to stimulate spending. The payoff has been evident, as tourism and spending rebounded during last week's busy Golden Week holiday period.

Europe is failing to get a grip on the virus

The Covid-19 crisis had gone from bad to worse in Europe. In Germany, almost all large cities are now coronavirus hotspots. The positivity rate has skyrocketed in Paris, as France added more cities to the "maximum alert" category. Residents of Madrid have been banned from leaving their neighborhoods, except to go to work, to school, go to the doctor and a few other exceptions. In the UK, Prime Minister Boris Johnson is expected to announce a new tiered system for restrictions later today.

ON OUR RADAR

India's health minister urged people to stay home during festivals after the country's number of reported cases topped 7 million.New York's Roosevelt Hotel is closing after nearly 100 years because of the pandemic.A woman has lost hearing in one ear after a mild Covid-19 infection. She is not the first one — there's growing evidence that the coronavirus may sometimes cause sudden hearing loss. Former New Jersey Governor Chris Christie has been released from the hospital following treatment for the coronavirus.Scotland's whisky islands are dealing with a major Covid hangover.10,000 mink died in Covid-19 outbreaks at US fur farms; it appears the virus spread from human to mink.

TODAY'S TOP TIP

Covid-19 is worsening homelessness and housing insecurity. According to UN-Habitat, 100 million people worldwide are homeless, and at least 1 billion live in inadequate housing or overcrowded informal settlements.

These already high numbers are surging due to the pandemic's economic impact, and now having a safe place to call home has become even more challenging for people around the world. Here's how you can help.

TODAY'S PODCAST

"For a vaccine to actually work, it's got to not only be safe and effective, but also be accessible and trusted. And that's why it's so important that it not get politicized." -- Dr. Tom Frieden, CDC director 2009-2017

CNN's most recent global town hall featured a conversation with five former CDC directors about how the US is handling this pandemic. Check out today's episode for excerpts from the special, hosted by Chief Medical Correspondent Dr. Sanjay Gupta and anchor Anderson Cooper. Listen Now.