(CNN) -- Coronavirus cases continued to spread in parts of the American south and west in the past week as experts warn that packed protests could exacerbate the pandemic.
The early parts of the American coronavirus outbreak struck hardest in the dense metropolitan areas on the coasts, such as New York, New Jersey, Boston, and California. But the last few weeks have seen wider spread in inland states, including Arkansas, Texas and Arizona.
In Arkansas on Tuesday, Gov. Asa Hutchinson said there were 375 new positive coronavirus tests, the highest single-day number of new community cases. There are currently more people hospitalized with Covid-19 there than at any prior point.
"We continue to trend upward in the number of cases," Hutchinson said.
Arizona added 1,127 new positive Covid-19 cases on Tuesday, the state's highest single-day total in the pandemic. Texas, too, has seen over 1,000 new positive coronairus cases in six out of the last seven days.
In total, the US has over 1.8 million cases and over 106,000 deaths, both by far the most of any country in the world.
In addition, health officials have expressed concern about a renewed outbreak stemming from the nationwide protests against the police killing of George Floyd.
CNN chief medical correspondent Dr. Sanjay Gupta said that the coronavirus could spread at protests depending on factors like mask-wearing, how closely people gathered, and how long people stayed in close contact.
"i think it's fair to say that there is going to be an impact," Gupta said Wednesday.
"It is a contagious virus. People being outside, people wearing masks, people moving by each other more quickly may reduce the likelihood of significant exponential growth. But that's still the concern."
For example, Oklahoma State football player Amen Ogbongbemiga said in a tweet on Tuesday that he tested positive for Covid-19 after attending a protest.
"After attending a protest in Tulsa AND being well protective of myself, I have tested positive for COVID-19," Ogbongbemiga tweeted. "Please, if you are going to protest, take care of yourself and stay safe."
The virus has particularly impacted African-Americans, who make up a disproportionate percentage of Covid-19 cases and deaths.
Worldwide, Covid-19 cases are increasing most rapidly in parts of Latin America. Brazil now has the second-most cases of any country in the world, and Peru, Chile and Mexico all among the top 15 countries with the most cases, according to data compiled by Johns Hopkins University.
What will stop the virus -- and what won't
Entering the sixth month of the virus, public health officials are more clearly seeing what stops the virus from spreading and what doesn't.
For one, the textbook combination of identification, isolation and quarantine for contacts helped stop the potential spread of coronavirus an Air Force basic training camp. Military doctors said their approach kept the case count to just five among 10,000 recruits at Joint Base San Antonio-Lackland in Texas in March and April.
The base used techniques including quarantine, social distancing, early trainee screening, rapid isolation and monitored re-entry to slow the transmission, the researchers said in a report published by the US Centers for Disease Control and Prevention Tuesday.
"Beginning March 17, all new recruits were segregated upon arrival for a two-week arrival quarantine on an area of the base separated from the main cohort of trainees," Dr. Joseph Marcus of the Brooke Army Medical Center and colleagues wrote in their report. "In addition, all trainees were instructed to maintain a distance of at least 6 feet between one another to ensure social distancing."
In April, the use of face coverings was made mandatory. The strategies put into place at the base meant that the rate of infection was significantly lower than that of other communal living environments, such as homeless shelters.
On the other hand, warmer weather is unlikely to stop the spread of coronavirus, Dr. Francis Collins, the director of the National Institutes of Health, said in a blog post Tuesday.
"Climate only would become an important seasonal factor in controlling COVID-19 once a large proportion of people within a given community are immune or resistant to infection," Collins wrote, citing experts in infectious disease transmission and climate modeling.
"We'll obviously have to wait a few months to get the data. But for now, many researchers have their doubts that the COVID-19 pandemic will enter a needed summertime lull," he added.
Collins is just the latest expert to throw cold water on the theory, boosted by President Donald Trump, that speculated heat would lessen the spread and possibly kill the virus altogether.
Dr. Fauci optimistic about vaccine
The US should have 100 million doses of one candidate Covid-19 vaccine by the end of the year, Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases (NIAID) and a member of the White House coronavirus task force, said Tuesday.
"Then, by the beginning of 2021, we hope to have a couple hundred million doses," Fauci said during a live question and answer session with the Journal of the American Medical Association.
It's still not clear whether the vaccine will be effective against the novel coronavirus. Still, Fauci expressed optimism that one of the many vaccine trials would be successful.
"I'm cautiously optimistic that with the multiple candidates we have with different platforms, that we are going to have a vaccine that will make it deployable," Fauci said.
CNN's Jen Christensen, Naomi Thomas and Shelby Lin Erdman conributed to this report.