Florida, Mississippi, Hawaii, and Oregon hit new peaks for daily COVID-19 cases and hospitalizations.
Oregon and Hawaii, with higher vaccination rates and mask mandates, have more room left in ICU.
They may never reach the "precarious position" of Florida and Mississippi, a professor said.
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Four US states have set records for new COVID-19 infections and hospitalizations over the past few days, data from Johns Hopkins University shows.
Florida recorded more than 151,000 new cases on Friday, and Hawaii reached 1,167 new infections - both the highest since the start of the pandemic in those states. On Monday, Mississippi recorded 7,839 cases, and Oregon 4,380, which are the highest in the states since the pandemic began.
The daily number of hospitalizations is also at an all-time high in these four states, the data showed
But of the four states, those with higher vaccination rates - Oregon and Hawaii - have more room left in ICU, suggesting vaccines are reducing severe infections.
Peter Chin-Hong, professor of Medicine at University of California in San Francisco, told CNBC that Oregon and Hawaii were "hurting with explosive case rates, but with high vaccination and masking rates, may not ever be in the same precarious position" as Florida or Mississippi.
Florida and Mississippi's ICUs are at more than 90% capacity and are mostly full of COVID-19 patients, the Johns Hopkins University data showed. Oregon and Hawaii's ICUs are more than 73% full, with mostly non-COVID-19 patients.
Oregon and Hawaii have mask mandates in place, while Florida and Mississippi don't.
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Hawaii and Oregon have fully-vaccinated 61.3%, and 58% of their population respectively, according to Johns Hopkins University - well above the 50.8% national average.
Meanwhile, 51.8% of Floridians are fully vaccinated and Mississippi's vaccination rates are much lower, at 36.1%, the same data shows.
Mississippi Gov. Tate Reeves said at a press conference on Friday that "when you look across the country, to a certain extent, this current wave is the pandemic of the unvaccinated."
"Those who received the vaccine are significantly less likely to contract the virus," he said.