Editor’s note: If you haven’t seen these headlines, be sure to check them out first thing Friday.

The president appears to have claimed Thursday that this vaccine is a "game changer" for treating hemorrhagic fever, but Dr. Raymond Yeung told the New York Times that his research would never have received the kind of praise unless there was data to support it.

“I thought it was outrageous and unethical to have the public funding of a research project use live virus rather than a synthetic version of an experimental vaccine or a viable safety study,” Dr. Yeung told the Times. “That is only used in people who are at risk for serious complications of the actual disease.”

Our colleague Bonnie Taub-Dix, a former childhood immunization expert at the Centers for Disease Control, has said she believes the use of live virus in animals in developing drugs such as this would pose a risk to humans. “There are always biological dangers associated with all animal-derived products,” Taub-Dix said.

Here are some of the latest developments in the controversy:

• A national scientist asked by President Donald Trump to oversee the development of a vaccine against the new coronavirus thinks a strong dose of skepticism is needed to ensure the process actually leads to a vaccine that benefits the public. Trump cited the proposed CDC grant as a major step forward in protecting against the virus, the deadliest disease outbreak in the United States since Ebola.

"The horse is out of the barn," Trump said Thursday at a White House briefing.

But CNN’s chief medical correspondent, Sanjay Gupta, is skeptical that a vaccine can be developed quickly. Dr. Raymond Yeung, the former CDC immunization expert who was asked to oversee the project, agrees.

“My academic background — and I was in this field for 20 years — is to be skeptical about [testing]. There’s a lot of optimism about new technologies, but I’m still concerned that the creation of a live vaccine would have value for the public health,” Dr. Yeung told Gupta.

“All other vaccines have been from syringe shots or finished cell lines. Dr. Yeung explains a live virus vaccine from a deactivated or live H5N1 bird flu virus would require donors with antibodies to H5N1, but would have almost no chance of benefiting those without immunity from the bird flu virus.”

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• The virus that originated in a pigeon’s respiratory system appears to be slowly mutating into a life-threatening human respiratory infection, and it has become the deadliest known disease outbreak in the United States.

Last week, the Centers for Disease Control announced it would put an experimental drug — ZMapp — on a priority list for use in treating those with the respiratory disease. While that drug is made from a genetically engineered virus, a different type of virus could be used in creating a vaccine against the new, fast-spreading virus, The New York Times reports.

Jeffrey Sachs, a Columbia University infectious disease expert, has said the virus “may soon overwhelm the supply of a drug” that is already used to treat severe respiratory infections.

That leaves scientists at the forefront of studying the virus with only a glimmer of hope that an effective vaccine may be developed soon. Dr. Yeung has likened that task to that of building the best engine in the world, and then having a different car drive by trying to figure out why it crashes.

“I would be hesitant about taking a sample of this virus, just in case we can’t get the right vaccine strategy,” Dr. Yeung told Gupta.

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