For Trump, G.O.P. Created an Alternative America Beyond Covid-19

In fact, convalescent plasma has been used by doctors for decades, and with coronavirus patients since the early days of the outbreak. Its effectiveness, however, is still in question and has most likely been exaggerated by the administration, and because it must be made from blood donations from Covid-19 survivors, its availability is expected to be limited.

As for a vaccine, it is impossible to predict when one will become availability with certainty. A few drug makers are far along in testing their vaccines, but the process then includes securing F.D.A. approval, ramping up manufacturing and setting up a distribution system — an awful lot to pack into the next four months.

Nevertheless, Mr. Trump sounded an optimistic note, saying that there would be “a vaccine before the end of the year or maybe even sooner.”

The coronavirus pandemic shows little sign of abating in the United States, with nearly 6 million total cases and an average of 42,000 new daily cases. The campaign of former Vice President Joseph R. Biden Jr. noted Friday that at least 3,525 Americans had lost their lives to the coronavirus since the Republican convention began on Monday. (The New York Times counted 4,037.)

“Instead of a strategy to overcome the pandemic, or any concern for the unbearable suffering in our country right now as a result of his ongoing failures, what we heard was a delusional vision completely divorced from the crushing reality that ordinary Americans face,” Kate Bedingfield, a Biden deputy campaign manager, said.

Such numbers did not stop Mr. Trump from declaring the country’s response to the pandemic a great success.

“Joe Biden’s plan is not a solution to the virus, but rather it is a surrender to the virus,” he said. “My administration has a very different approach. To save as many lives as possible, we are focusing on the science, the facts and the data.”

Katie Thomas and Carl Zimmer contributed reporting.