RALEIGH — After several weeks of surging, new COVID-19 cases have been coming back down in North Carolina since mid-September.
Vaccinations did increase for a few weeks throughout July and August, which could be due to fears of the delta variant, a mutation of the coronavirus that’s more than twice as contagious as the original strain, according to the Centers for Disease Control and Prevention.
But vaccine rates have decreased week-to-week since late August, even as delta has waned, N.C. Department Health and Human Services data show.
With 54% of the North Carolina population fully vaccinated as of Friday, nearly 5 million people are unvaccinated statewide, according to 2020 population estimates from the CDC.
And with a DHHS analysis concluding in late August that those unvaccinated are four times more likely to contract COVID-19, it would seem that case counts would remain high, but they haven’t.
Why are cases going down?
In the week prior to Friday, Oct. 8, DHHS reported nearly 25,000 new cases of COVID-19 statewide. The week before that, about 31,500. And the week before that, over 38,000.
In early September, at the height of the delta surge, the state reported over 50,000 new cases in a week.
And vaccinations decreased from August to September.
In the four weeks from Aug. 9 to Aug. 30, 643,340 doses were administered statewide. In the four weeks after, it dropped to 470,471.
Dr. David Wohl, infectious disease expert at UNC-Chapel Hill, attributed the drop in cases to more immunity, both natural and by vaccine.
“There’s always a peak, and a peak means it’s followed by a decline, and declines happen after surges for a variety of reasons,” Wohl said. “One reason is the number of susceptible people who are in a position to be infected starts to decrease.”
Even as vaccinations started to wane, Wohl said, vaccine rates did increase over late July and much of August. And those who are infected and survive maintain some immunity for a time.
“There’s more immunity every day than there was before,” Wohl said.
Immunity obtained from the vaccine, however, is better than that from natural infection, he said.
In a population sample taken by DHHS from March 2020 to last month, there were 10,812 reinfections. Of those, just 200 were vaccinated.
“The vaccinated people were much, much, much less at risk for reinfection. So natural infection didn’t cut it,” Wohl said.
For those still susceptible, Wohl said they may not be at the same risk as those already infected.
COVID-19 spreads best in environments where people are unmasked and not socially distanced inside for a prolonged period of time — like prisons, schools and nursing homes.
“The people who are the low hanging fruit for getting infected, get infected. And then people who are less likely to get infected start to make up more of the unvaccinated susceptible population,” Wohl said.
A pattern of surges
After the first case of COVID-19 was detected in North Carolina in March 2020, the state saw it’s first increase of cases in May. That surge peaked in July.
Cases saw their biggest surge after Thanksgiving last year, lasting until mid-January.
The delta surge started in July and peaked last month.
Overall, North Carolina like the rest of the country and the world has followed surges that lasted for about two months each.
Wohl said the science behind the pattern is complicated, but he attributed it to weather patterns, human behavior and holiday gathering.
“Temperature and climate does play a role in transmission of respiratory viruses,” Wohl said. “When it gets colder, people are more likely to be indoors. Sometimes people are more likely to be indoors because it’s really hot.”
“We also have holidays that punctuate our calendar. And some of these are our times when we have gatherings,” he said.
Is another surge coming?
With Thanksgiving less than two months away, Wohl said he’s concerned that another surge is coming.
“A welcome decrease in new cases and deaths might be countered by colder weather and Thanksgiving. I think people are going to gather for Thanksgiving thinking they’re better protected than they are. I think there will be people who are not fully vaccinated with people who are fully vaccinated,” Wohl said. “I would be shocked if we don’t see a bump towards the later part of this year due to Thanksgiving and the colder weather.”
And Wohl said he doesn’t think delta is done. The latest CDC data show that more than 97% of sequenced virus in North Carolina is delta.
He recommended that people not gather inside and unmasked with those who are not part of their household, regardless of vaccination status.
According to data from DHHS, the two deadliest months of the pandemic came immediately after Thanksgiving last year— 2,102 people died in December and 3,039 in January.
From Aug. 1 until now, before and after delta peaked, 3,253 North Carolinians have died due to COVID-19.