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An epidemiologist from the University of Alabama at Birmingham has projected that the country and Alabama could achieve herd immunity against COVID-19 as early as May or June.
“We are getting closer to herd immunity, thanks to the vaccine, and also new scientific data that shows us that more people had COVID than they have been tested,” said Suzanne Judd, doctoral epidemiologist at the ‘UAB.
Judd said his calculations were based on the current pace of COVID-19 vaccine distribution, coupled with a recent Columbia University study that estimated that more than a third of the U.S. population may already have been infected with the virus at the end of January.
Collective immunity occurs when the virus cannot spread through an uncontrolled population because enough members of the population have some kind of immunity, either from a vaccine or from antibodies if they had the disease and were recovering.
Scientists 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 have contracted the virus who have never been tested.
If that number is high enough, the spread of the disease could drop dramatically in the coming months.
“According to current estimates, we will see [herd immunity] late spring, early summer in Alabama, ”Judd said. “Somewhere between May and June is likely, but that depends on many factors.”
Judd said new studies at Columbia, Johns Hopkins University and UAB suggest many more people have already had the disease than we thought. In New York City, she said, a study showed an almost 10-to-1 ratio between people who currently have antibodies and people who test positive for the virus.
Judd said it was less surprising because New York was hit hard by the virus early in the pandemic, when it was much more difficult to get a COVID test. She told UAB the ratio is closer to 5 to 1. Her forecast, in an attempt to be cautious and not overestimated, assumes that there are three people who have actually had COVID in Alabama for every positive test reported. .
“The more people who are immune, the less the virus spreads, the safer it will be for us to interact with each other again,” Judd said.
Estimates vary on the proportion of the population that must be immunized to truly disrupt the spread of the virus, but Judd said his calculations were based on a threshold of immunity in 72% of the population.
“There is no magic number that is collective immunity,” Judd said. “Every virus, every bacteria is different, and they mutate at regular intervals, so that number can move around. But right now, scientists are shooting around 72% of the immune population, so hopefully we’ll see that soon.
For Alabama, Judd said that would mean 3.5 million people need to be vaccinated or infected. Current statistics show that 12.5% of Alabama’s population had received at least one dose of the COVID vaccine and 10% had tested positive for the virus.
Alabama had reported 491,849 positive tests as of Friday. Assuming a 3-to-1 ratio, this would indicate that nearly 1.5 million Alabamians have already had COVID. If the 5-to-1 ratio turns out to be true, that would equate to more than 2.4 million people having already been infected, bringing the state closer to that herd immunity threshold.
Alabama state health official Dr Scott Harris said he was familiar with Judd’s work and said she had done a “terrific job” in providing for herd immunity for the ‘Alabama.
“Dr. Judd is a great researcher, so I think what she put together was very intriguing and makes a lot of sense, ”Harris said Thursday.
Still, Harris said there were many unknowns about the herd’s immunity, including how many Alabamians have already had COVID but never been tested.
“Just over about 10% of our condition that we know of has tested positive and been infected,” Harris said. “But the percentage of antibodies on board is certainly much higher than that.”
Mutations could also be key to whether the herd’s immunity resists, she said, or whether booster vaccines are needed.
“It really depends on how the virus mutates,” she says. “There are certain mutations that we will be completely covered by the immune response the body has already developed. There are other mutations that could escape the immune system and require a vaccine booster or lead to reinfection.
“Variants are therefore something that we have to watch very carefully.”
Judd said the Alabamians should not let their guard down or start leaving their masks at home just yet.
“We’re not going to know we’re at herd immunity, there’s no magic, all of a sudden we’re at 72% and we’re safe,” Judd said. “The things that we are going to monitor are the number of cases per week, we will continue to monitor this very carefully. And as long as it tends down and stays below about 10 or 5 [cases] per 100,000, and we’ve got decent testing in the state, so we’ll know it’s safe to bring people together.
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