An epidemiologist at the University of Alabama in Birmingham expected that the country and Alabama could achieve herd immunity to COVID-19 as early as May or June.
“We are getting closer to flock immunity thanks to the vaccine and also new scientific data showing us that more people had COVID than were tested,” said Suzanne Judd, PhD epidemiologist at UAB.
Judd said her calculations are based on the current pace of delivery of COVID-1
Herd immunity occurs when the virus cannot spread through a population uncontrolled because enough members of the population have some form of immunity, either from a vaccine or from antibodies, if they had the disease and recovered.
Researchers already know how many people have been vaccinated against COVID and how many people have tested positive for the disease. But there are a huge and unknown number of people who got the virus and were never tested.
If the number is large enough, the spread of the disease could drop dramatically in the coming months.
“Current estimates are that we will see [herd immunity] sometime in late spring, early summer in Alabama, ”Judd said. “Somewhere between May and June is likely, but it depends on many factors.”
Judd said new studies at Columbia, Johns Hopkins University and UAB suggest that many more people may have already had the disease than we thought. In New York City, she said, a study showed a ratio of nearly 10 to 1 of people who currently have antibodies to people who tested positive for the virus.
Judd said it’s less surprising because New York was hit hard by the virus early in the pandemic, as it was much harder to get a COVID test. She told UAB that the ratio is closer to 5-to-1. Her prognosis, in an attempt to be conservative and not overestimated, assumes that there are three people who actually had COVID in Alabama for every reported positive test.
“The more people who have immunity, the less the virus spreads, the safer it becomes for us to interact with each other again,” Judd said.
Estimates vary depending on how much of the population needs to be immune to really disrupt the virus spread, but Judd said her calculations were based on a threshold for gaining immunity in 72% of the population.
“There is no magic number, there is herd immunity,” Judd said. “Every virus, every bacterium is different, and they mutate at regular intervals so that this number can move. But at the moment, researchers are shooting at about 72% of the population with immunity, so hopefully we will see that soon. ”
For Alabama, Judd said it would mean 3.5 million people would either have to be vaccinated or infected. Current statistics show that 12.5% of Alabama’s population had received at least one COVID dose of vaccine, and a further 10% had tested positive for the virus.
As of Friday, Alabama had reported 491,849 positive tests. Assuming a ratio of 3 to 1, this would indicate that almost 1.5 million Alabamers have already had COVID. If the 5-to-1 ratio turns out to be true, it would equal more than 2.4 million people who have already been infected, bringing the state closer to this herd immunity threshold.
Alabama State Health Officer Dr. Scott Harris said he was familiar with Judd’s work and said she did a “huge job” predicting herd immunity for Alabama.
“Dr. Judd is a great researcher, and so I think what she put together was very exciting and makes a lot of sense, ”Harris said on Thursday.
Still, Harris said there were many unknowns about herd immunity, including how many Alabamers may have already received COVID but were never tested.
“Just over 10% of our condition, as we know it, has tested positive and has been infected,” Harris said. “But certainly the percentage who have antibodies on board is much higher than that.”
Mutations can also be the key to whether herd immunity lasts, she said, or if booster vaccines are needed.
“It really depends on how the virus mutates,” she said. “There are some mutations that we will be completely covered by the immune response that the body has already developed. There are other mutations that can escape the immune system and require a vaccine boost or actually lead to reinfection.
“So the variants are something we have to look at very carefully.”
Judd said Alabamians should not let their guard fail or start leaving their masks at home yet.
“We do not know we are at herd immunity, there is no magic, suddenly we are at 72% and we are safe,” Judd said. “The things we need to monitor are the number of cases per week, we will continue to look at it very closely. And as long as it falls down and stays below approx. 10 or 5 [cases] pr. 100,000, and we have decent tests in the state, so we know it’s safe to get people back together. ”