As of September, the vast majority of Americans did not have coronavirus antibodies, according to a new study published in JAMA Internal Medicine.

These data matter as the coronavirus spreads rapidly throughout most of the country, most people remain vulnerable to it.

Across the U.S., the portion of states’ populations with detectable antibodies ranged from less than 1% to 23%. In most places, less than 10% of the population had them as of September.

• The portion of people with antibodies was often lowest in older age groups — an ominous sign.

Emerging evidence suggests that antibodies wane over time. In New York — the epicenter of the spring’s outbreak — the percentage of people with antibodies decreased from 23.3% in the first collection period to 17% in the final one.

Scientists are also discovering that antibodies may not be the body’s only form of protection against the coronavirus, and how immunity works is still unclear.

As bad as the spring was in the Northeast, only a fraction of those states’ populations actually got sick.

• The surge of cases over the last few weeks, particularly in the Midwest and West, could easily have bumped other states up the list. But in most of the country, there is still plenty of human fuel to feed the coronavirus fire.