As the impact of social distancing is being felt in dwindling economies, stir-crazy households and cash-starved businesses around the world, discussions of creating herd immunity have arisen, begging the question: Could letting everybody out be a quicker way out of this mess?
What that would look like is basically what is happening in Sweden — people practicing some degree of social distancing but restaurants and bars remaining open, borders remaining open and lots of businesses carrying on as usual while, in theory, the virus that causes COVID-19 infects so many people there are not enough hosts left for it to survive.
According to Swedish epidemiologists, herd immunity in that country could be established within two weeks.
But the Swedish experiment is filled with holes, said Dennis Carroll, senior fellow at the Bush School of Government and Public Service at Texas A&M University, formerly a senior infectious diseases advisor for the U.S. Centers for Disease Control and Prevention.
“Sweden started acting like they were in Las Vegas,” Carroll said. “Basically they took a big gamble without any information like whether there is protective immunity for COVID-19 and which populations need to be protected.”
Several ingredients are required for herd immunity to work, Carroll said. The first is that people have developed protective immunity.
The best way to do that, with many diseases, is with a vaccine — enough people are immunized with antibodies to halt the disease’s spread.
Think of measles, a disease that once you’ve had it, you’ll never have it again. Or the measles vaccine that, when widely used, effectively prevents the disease from reappearing.
“With measles, there’s a sterilizing immunity that’s long-lasting,” said Dr. Richard Rupp, professor of pediatrics at the University of Texas Medical Branch.
“With herd immunity minus a vaccine, it depends on the notion that once you’ve had it, you don’t get it again,” Rupp said.
Bottom line: We don’t know that about COVID-19, he said.
Other coronaviruses, such as those that cause the common cold, occur repeatedly, some as often as every year.
“We get them over and over again,” Rupp said. “Having the infection doesn’t generate longstanding herd immunity.”
COVID-19, a brand-new coronavirus, has not been investigated enough at this point to determine whether it behaves the same as seasonal coronaviruses.
“If it turns out that it’s more like seasonal coronaviruses or influenza or a whole bunch of viruses we get over and over again in our lifetime, there really won’t be big role for creating herd immunity for COVID-19,” Rupp said.
PROTECTING THE VULNERABLE
The second ingredient for creating successful herd immunity is measuring the adverse effects, Carroll said.
“Can we begin to differentiate between populations that are more vulnerable to illness and death if infected? We’re getting clear information on this about COVID-19,” he said. “Most deaths are really occurring among people 60 years or older, and people with preexisting conditions like heart disease and diabetes.”
If the first criteria is met and it turns out COVID-19 does give protective immunity to those it infects, communities could then think about letting all people out or asking whether some people need to be held back.
“You’d have to hold back the high-risk groups,” Carroll said.
Sweden’s casual approach has led to the highest COVID-19 mortality numbers in Scandinavia, Carroll said. That’s because they were sloppy about protecting elderly people in nursing homes and adequately protecting those at high risk, he said.
“To create a successful herd immunity, if it all lines up and you can clearly state that 50 to 60 percent of the population have protective immunity, you’d let all the people under 60 or so, all the people not living with heart disease or diabetes back to work and out in the world, and the rest would stay at home. Then when everybody else has been infected, you start letting those at risk out,” Carroll said.
The idea is that when a big enough portion of the population has immunity against the virus, the virus has nowhere to go and transmission stops, Rupp said.
“If your body is immune, the virus needs to get into the next person. And if it doesn’t do that, it dies in you,” he said. “If you’re only surrounded by immune people, the virus can’t keep going.”
A UNIFIED STRATEGY
The two big ifs required to create a successful herd immunity — protective immunity from the virus and protection for the most vulnerable — precede other considerations a community must think about before it decides to just let everybody go their way.
One of those considerations is mobility and whether there are people moving in and out of a community who may not have protective immunity.
Galveston is a good example — a place with a relatively small population on an island but with millions of tourists coming and going on a regular basis.
“Let’s assume Texas goes for her immunity and you get 60 percent of the population with protective immunity, but then there are all these other people flying in from all over the place and that messes everything up,” Carroll said.
That is why a well-considered, unified and coordinated national approach is necessary for any kind of strategy, such as establishing herd immunity, to work, and we don’t have one, he said.
“A strategy like this needs to be seriously considered. We can’t be locked down forever,” Carroll said. “But we need to make sure of many things first.”
One of those things is an adequate supply of antibody testing that’s high quality, he said.
Antibody tests would show, among other things, who in the population already has been infected and, presumably, has protective immunity, at least until a vaccine is developed.
But the tests need to be consistently reliable. Problems with early antibody tests related to COVID-19 documented in a recent New York Times report include loose Food and Drug Administration regulation, allowing manufacturers to validate their own tests and risking a market flooded with inconsistent tests; confusing federal guidance about how to use the tests; and tests with a false high positive rate.
“The tests right now are all over the place,” Carroll said. “All of that needs to be tightened up so we can get clearer answers.”