An epidemiologist at the University of Alabama at Birmingham projected that the country, and Alabama, could achieve collective immunity to COVID-19 as early as May or June.
“We are getting closer to collective immunity, thanks to the vaccine and also new scientific data that shows us that more people have had COVID than those tested,” said Suzanne Judd, PhD epidemiologist at UAB.
Judd said his calculations are based on the current pace of delivery of the COVID-19 vaccines, along with a recent Columbia University study that estimated that more than a third of the U.S. population may already be infected with the virus by the end of January. .
Herd immunity occurs when the virus cannot spread through an uncontrolled population because a sufficient number of members of the population have some form of immunity, whether from a vaccine or antibodies, if they have the disease and recover.
Scientists already know how many people have been vaccinated against COVID and how many have had positive results for the disease. But there are a huge and unknown number of people who have contracted the virus and have never been tested.
If that 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, ”said Judd. “Somewhere between May and June it 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 an almost 10 to 1 ratio of people who currently have antibodies to people who tested positive for the virus.
Judd said this is less surprising because New York was hit hard by the virus at the beginning of the pandemic, when it was much more difficult to do a COVID test. She said at UAB, the ratio is closer to 5 to 1. Her prediction, in an attempt to be conservative and not overestimate, assumes that there are three people who actually had COVID in Alabama for each reported positive test.
“The more people have immunity, the less the virus will spread and the safer it will be for us to interact with each other again,” said Judd.
Estimates vary about how much of the population needs to be immune to actually stop the virus from spreading, but Judd said his calculations were based on a limit on obtaining immunity in 72% of the population.
“There is no magic number that is the herd’s immunity,” said Judd. “Each virus, each bacterium is different and they mutate at regular intervals, so that number can move. But at the moment, scientists are shooting at about 72% of the population with immunity, so hopefully, we’ll see that soon. “
For Alabama, Judd said that means that 3.5 million people need to be vaccinated or infected. Current statistics show that 12.5% of the population of Alabama received at least one dose of the COVID vaccine and another 10% tested positive for the virus.
As of Friday, Alabama reported 491,849 positive tests. Assuming a 3 to 1 ratio, this would indicate that almost 1.5 million Alabamians have had COVID. If the 5 to 1 ratio is true, that would amount to more than 2.4 million people already infected, bringing the state closer to the herd’s immunity limit.
Alabama state health officer Dr. Scott Harris said he was familiar with Judd’s work and said she did an “incredible job” providing for collective immunity for Alabama.
“Dr. Judd is a great researcher, so I think what she put together was very intriguing and makes a lot of sense, ”said Harris on Thursday.
Still, Harris said there are many unknowns about collective immunity, including how many Alabamians may have taken COVID, but have never been tested.
“A little more than 10% or more of our state we know has tested positive and been infected,” said Harris. “But certainly the percentage of antibodies on board is much higher than that.”
Mutations may also be essential in determining whether collective immunity is maintained, she said, or whether 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 boost in the vaccine or even lead to reinfection.
“Therefore, variants are something that we must observe very carefully.”
Judd said that Alabamians should not let their guard down or start leaving their masks at home yet.
“We will not know that we have collective immunity, there is no magic, we are suddenly at 72% and we are safe,” said Judd. “What we are going to monitor is the number of cases per week, we will continue to watch very carefully. And, as long as the trend is down and stays below about 10 or 5 [cases] for 100,000, and we have decent tests in the state, so we’ll know it’s safe to bring people together again. “