From How to prevent the next pandemic (Bill Gates, 2022) p97-100
Depending on which country you live in, if you tested positive for COVID, you may have been called by someone asking about all the people you might have come into contact with. They probably focused specifically on the forty-eight hours before you first started feeling sick (if you did feel sick). This is the process known as contact tracing.
Although it felt new to many people around the world during COVID, contact tracing is actually an old strategy. It was essential to eradicating smallpox in the twentieth century and is also at the center of strategies to fight Ebola, tuberculosis, and HIV in the twenty-first.
Contact tracing works best in countries that excel at testing and processing data — among them, South Korea and Vietnam. But both of those countries did things that wouldn’t fly in the United States. Under a law changed after the 2014 outbreak of Middle East Respiratory Syndrome, or MERS, the South Korean government used data from credit cards, mobile phones, and surveillance cameras to trace the movements of infected people and identify other people they had come in contact with. It published this information online, though it had to restrict some of the data after regional governments gave out too many details about people’s movements. According to the journal Nature, one man “was wrongly accused of having an affair with his sister-in-law because their overlapping maps revealed they dined together at a restaurant.”
Vietnam also used posts on Facebook and Instagram, along with mobile phone location data, to supplement extensive face-to-face interviews. In March 2020, before the country was testing every Passenger arriving from the U.K., a flight from London arrived in Hanoi with 217 passengers and crew. Four days later, a patient went to the hospital with symptoms and tested positive for COVID. Vietnamese authorities tracked down all 217 people from the flight and identified 16 more cases among them. Everyone on the plane and more than 1,300 of their contacts were quarantined. In all, there were 32 cases related to the flight, a small fraction of the cases that would’ve happened if all those passengers and crew members had simply gone on their way.
If you read the previous two paragraphs and thought, if anyone calls me about contact tracing, I’m not picking up the phone, you’re not alone. In two counties in North Carolina, many of the contacts who were named never returned the tracer’s phone call. And between a third and half of COVID-infected people who were reached claimed not to have had contact with a single person in the days before they tested positive. But contact tracing will often be an important part of stopping the spread of a disease, which is why we have to figure out how to build trust between public health agencies and the public so that more people will share their contacts.
One of the reasons people hesitate to respond is the fear that their contacts will have to go into quarantine, but, fortunately, broad quarantines of every single contact might not always be necessary. In England, some schools had their students stay home for ten days if they had come into contact with someone who had COVID. Other schools allowed kids to keep coming to class as long as they tested negative every day. This daily testing, it turns out, was just as good at preventing outbreaks, but without having to keep students home from school.
And contact tracing can still be effective even if it’s not done as intensively as Vietnam and South Korea did it. In general, if you start the program when only a small fraction of the population is infected, and if you identify a large share of cases in your country, contact tracing can cut transmission by more than half.
Some U.S, states and other governments rolled out smartphone apps that helped identify possible contacts, but I’m skeptical that these apps will ever be effective enough to be worth a big investment of money or time. For one thing, their usefulness is capped by the number of people who install them, because the apps only record an exposure if both parties who come into contact with each other are using them. I suspect that most of the people who use these apps are also the ones who would follow lockdown guidelines—and if you’re doing that, you should have so few contacts that you can probably remember them all. For the people who really are sheltering in place, getting a message that says “Hey, you saw your brother” won’t be very helpful.
During COVID, one challenge with conventional contact tracing is that it’s not an especially efficient use of resources, because the virus is not transmitted at the same rate by everyone who’s infected. If you get the original COVID strain, the chances are not especially high that you’ll pass it along to someone else. (About 70 percent of those cases may not transmit to anyone else at all.) But if you do pass it along to someone else, you probably pass it along to many people. For reasons we don’t entirely understand, 80 percent of COVID infections with early variants came from just 10 percent of the cases. (These numbers could be different for the Omicron variant — as | write this, we don’t have enough data to know.)
So with a virus like COVID, using the conventional approach means you’ll spend a lot of time finding people who wouldn’t have infected anyone else—epidemiologically speaking, you’ll find yourself in a lot of cul-de-sacs. What you really want to do is find the main thoroughfares, the relatively small number of people who are causing the most infections.
Understanding this limitation, a few countries tried a newer approach to contact tracing. Instead of working forward in order to find out whom they might have infected, these countries worked backward – identifying contacts up to fourteen days before the person started feeling sick. The goal was to find out who may have infected the patient, and then see who else that person may have passed the virus to.
Backward contact tracing is hard to pull off unless you have widespread testing, fast results, and a system for contacting people quickly, and it’s especially hard when you’re dealing with a pathogen that spreads fast, because there’s not much time between getting infected and becoming contagious. But where it was practical, the approach worked really well. It was used at locations in Japan, Australia, and other countries, and it proved quite effective at finding individuals who were superspreading the early COVID variants, One study found that it could prevent two to three times more cases than the traditional approach.
It’s stunning how little we know about superspreaders. What role does biology play? Are some people more prone to being a superspreader than others? There’s also certainly a behavioral component. Superspreaders seem not to pose more of a risk to small groups than other infected people do, but in crowded indoor public spaces, such as bars and restaurants, there’s a better chance that you’ll encounter one or more superspreaders, and they’ll have the opportunity to infect a lot of people. Superspreaders are one of the mysteries of disease transmission that needs a lot more study.
From p8
Throughout COVID, I’ve marveled at how I became the target of wild conspiracy theories. It’s not an entirely new sensation—nutty ideas about Microsoft have been around for decades—but the attacks are more intense now. I have never known whether to engage with them or not. If I ignore them, they keep spreading. But does it actually persuade anyone who buys into these ideas if I go out and say, “I am not interested in tracking your movements, I honestly don’t care where you’re going, and there is no movement tracker in any vaccine”? I’ve decided that the best way forward is to just keep doing the work and believe that the truth will outlive the lies.
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Where did the microchip vaccine conspiracy theory come from anyway?
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