An epidemiologist at the University of Alabama in Birmingham projected that the country and Alabama could already achieve herd immunity against COVID-19 in May or June.
“We are getting closer to herd immunity, thanks to the vaccine, and also new scientific data showing that more people had COVID than tested,” said Suzanne Judd, a PhD epidemiologist at UAB.
Judd said her calculations are based on the current rate of delivery of COVID-19 vaccines, along with a recent Columbia University study that estimates that more than a third of the U.S. population may be by the end of January with the virus was infected.
Herd immunity occurs when the virus cannot spread uncontrollably through a population, because enough members of the population have some kind of immunity, either against a vaccine or against antibodies if they have the disease and recover.
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 large and unknown number of people who got the virus and who have never been tested.
If the number is large enough, the spread of the disease could drop dramatically in the coming months.
‘Current estimates are what we will see [herd immunity] “Somewhere in the late spring, early summer in Alabama,” Judd said. “It’s probably between May and June, but it depends on a lot of factors.”
Judd said new studies at Columbia, Johns Hopkins University and UAB suggest that far more people may have had the disease than we thought. In New York City, she said, one study showed that there is an almost 10-to-1 ratio of people who have antibodies to people who have tested positive for the virus.
Judd said it was less surprising because New York was hit hard early in the pandemic, when it was much harder to get a COVID test. She says at UAB the ratio is closer to 5-to-1. Her prediction, in an effort to be conservative and not overestimate, assumes that there are three people in Alabama who actually had COVID for every positive test reported.
“The more people have immunity, the less the virus will spread, the safer it is for us to communicate with each other again,” Judd said.
Estimates vary depending on the amount of population that needs to be immune to actually disrupt the spread of the virus, but Judd said her calculations are based on a threshold for gaining immunity in 72% of the population.
“There is no magic number that is herd immunity,” Judd said. ‘Every virus, every bacterium is different and they mutate regularly so that this number can move. But at the moment, scientists with immunity are shooting at about 72% of the population, so hopefully we will see that soon. ”
For Alabama, Judd said that means 3.5 million people need to be vaccinated or infected. Current statistics show that 12.5% of Alabama’s population received at least one dose of COVID and another 10% tested positive for the virus.
As of Friday, Alabama reported 491,849 positive tests. Assuming there is a 3-to-1 ratio, this indicates that nearly 1.5 million Alabamians have already had COVID. If the 5-to-1 ratio turns out to be equal, it would equate to more than 2.4 million people already infected, bringing the state closer to the herd immunity threshold.
Scott Harris, Alabama’s state health officer, said he was familiar with Judd’s work and said she had done a “tremendous job” predicting the immunity of herds to Alabama.
“Dr. Judd is a good researcher, which is why I think what she put together was very interesting and makes a lot of sense,” Harris said Thursday.
Yet Harris said there are many unknowns about herd immunity, including how many Alabamians have already received COVID but never been tested.
“There is a little over 10% of our condition that we know has been positively tested and infected,” Harris said. “But definitely the percentage with antibodies is much higher than that.”
Mutations could also be key to whether herd immunity holds, she said, or if boost vaccines are needed.
“It really depends on how the virus mutates,” she said. ‘There are some mutations that we can completely cover up by the immune response that the body has already developed. There are other mutations that can escape from the immune system and require a vaccine boost or cause it to re-infect.
“The variants are therefore something we have to look at very carefully.”
Judd told Alabamians not to let their hats down, or to just leave their masks at home.
“We are not going to know that we have herd immunity; there is no magic, suddenly we are 72% and we are safe,” Judd said. ‘The things we are going to monitor are the number of cases per week. We will continue to look at it very carefully. And as long as it slopes downwards and stays below about 10 or 5 [cases] per 100,000, and we have decent tests in the state, then we will know that it is safe to get people back together. ”