Confounding factors might explain Florida's Covid surge

See What Went Wrong With the Pandemic in Florida by Patricia Mazzei, Benjamin Mueller and Robert Gebeloff of The NY Times. Excerpts:

"The best explanation of what has happened is that Florida’s vaccination rates were good, but not good enough for its demographics. It has so many older people that even vaccinating a vast majority of them left more than 800,000 unprotected. Vaccination rates among younger people were uneven, so clusters of people remained at risk. Previous virus waves, which were milder than in some other states, conferred only some natural immunity."

"The picture of who is dying, however, is complicated.

About 82 percent of people 65 and older in the state are fully vaccinated, about average for the nation. That has still left a relatively large number of older people — about 819,000 — unvaccinated or only partially vaccinated, said Jason L. Salemi, an epidemiologist at the University of South Florida. If the unvaccinated also take fewer other precautions, he added, that would put them directly in the virus’s path.

“The Delta variant is exceptional at finding vulnerable populations,” he said.

The situation in nursing homes, where infections can spread swiftly, has also been problematic. While vaccination rates among older Floridians as a whole have been good, the rate of nursing home residents who are fully vaccinated — an average of 73.1 percent in each home — is lower than every state but Nevada, according to the C.D.C. About 47.5 percent of nursing home staff members were fully vaccinated as of Aug. 15, the lowest of any state but Louisiana.

Older people are also more likely to have immune deficiencies and comorbidities, making them more susceptible to breakthrough infections and hospitalizations, noted Dr. Peter Chin-Hong, an infectious-disease specialist at the University of California, San Francisco. And some, though not all, data have suggested that immunity against infection has waned in older, vaccinated adults; the Biden administration has indicated that those people will be among the first in line for booster shots."

"Fifty-six percent of people between the ages of 12 and 64 in Florida’s 10 largest counties are fully vaccinated, which is consistent with national figures. But in the rest of the state, that figure is only 43 percent, and in 27 counties, less than 1 in 3 residents in the age group is fully vaccinated."

"Those who did not get vaccinated are only part of the explanation behind the surge. Many states slammed by the virus earlier developed deep reservoirs of natural immunity from prior infections, affording them higher levels of protection than would be evident from vaccination rates alone.

Not so in Florida. Compared to other states, Florida was spared as devastating a wintertime wave of cases as ravaged other parts of the country — in part because warm weather made it possible for people to gather outdoors. That was a boon to Florida’s economy and its political leaders but a liability come summertime, when the state was unable to rely on the same wall of natural immunity that is now helping to shield places walloped by the virus this winter.

“People have underestimated the role of natural immunity,” Dr. Chin-Hong said. “Wherever you get hit hard, you kind of get a reprieve from the virus.”

There is some question as to whether Florida’s vaccination rates, especially in places like Miami and Orlando, might have been inflated by tourists getting shots. Regardless, vaccinations appear to be making Covid-19 cases less severe in Miami-Dade County, which had one of the state’s highest vaccination rates, according to research by Dr. Jeffrey Harris, a physician and emeritus professor of economics at the Massachusetts Institute of Technology."