Some critics mocked the idea that Trump believed he could plan a convention in two months, an event that often takes two years to plan.
A small subset of GOP delegates will still gather in Charlotte, North Carolina, to formally renominate Trump on August 24.
"Leading by example, President Trump has put the health and safety of the American people first with his decision on the Jacksonville convention", said Bill Stepien, Trump 2020 campaign manager. "Yet, in many states people can drink in bars, get a haircut, eat inside a restaurant, get a tattoo, get a massage, and do myriad other normal, pleasant, but non-essential activities", the letter said.
"There's been this obsession with how many tests are we doing per day", said Dr. Tom Frieden, a former director of the Centre for Disease Control and Prevention (CDC).
It was scheduled to be held between August 24-27 in Jacksonville, Florida.
The Florida Education Association (FEA) filed a lawsuit this week against the state after Republican Gov. Ron DeSantis, a Trump loyalist, issued an emergency order forcing schools to reopen in less than a month.
The CDC's guidance highlights the challenges facing schools that have been instructed to reopen classrooms even as the US lacks substantive public-health tools to make doing so safely possible. President Trump has pushed heavily for reopening schools, but acknowledged on Thursday that some may need to delay reopening. Even as he tempered his position, Trump insisted that every school should be "actively making preparations to open".
Signs of hope are emerging in some regions.
Trump cancels Republican convention as virus soars
The list of donors to the now-canceled event reads like a who's who of industry titans, power brokers and wealthy Republicans. Ron Desantis about the decision, adding the state will "be doing very well very shortly".
Trailing the United States for the most confirmed cases is Brazil, with over 2,159,654, and India with 1,193,078.
Coronavirus deaths are now rising in 23 states and the country's three most populous states, Florida, Texas and California, top the list of 44 states where cases are increasing. Florida and California reported single-day records in fatalities with 173 and 157 deaths, respectively, on Thursday, the Wall Street Journal reported.
The better results in some parts of the country are being offset by worse outcomes in others.
"Infection rates in the U.S. are deeply troubling because the summer, when it's warmer, when people are outdoors more, actually it's easier to reduce the infection than it's going to be out in the fall", said Gates, who is helping fund the development of coronavirus vaccine efforts through his Bill and Melinda Gates Foundation.
"However, just like it was in April, leveling off is not enough - the goal is to suppress and not just mitigate".
More than 1000 deaths were reported on both Tuesday and Wednesday. This is considered dangerously high.
"I think it's much too early to tell", said William Schaffner, a health policy professor at Vanderbilt University.
The guidelines offer several ways to help reduce the spread of COVID-19, including keeping kids in pods, using social distancing, face masks, and frequent hand washing, as well as incorporating these measures in the curriculum. "I'm still pretty pessimistic".