We are nowhere near ‘herd immunity’
The coronavirus pandemic has shown clearly what happens when a new pathogen gets loose in a population where no one has had it before: It spreads like wildfire.
Long-familiar viruses, even ones that are every bit as contagious, can’t do that, because of a phenomenon called herd immunity.
It works like this: The more people there are in a community who have protective antibodies, either through vaccination or past exposure, the less likely an infected patient is to encounter someone who lacks them and pass the virus along. Above a certain threshold, the virus can’t spread readily enough for an outbreak to grow.
That’s why diseases like measles and chickenpox have become rare in the United States even though not everyone gets vaccinated: Enough people do to achieve herd immunity.
Epidemiologists don’t know yet exactly where the threshold is for the coronavirus, but they expect to find it somewhere between 60 and 80 percent of the population. Even New York City, the center of America’s worst outbreak, is still far below that: Only around 20 percent of residents tested in a survey in early May showed any antibodies, and that may be an overestimate.
“We don’t have a good way to safely build it up, to be honest, not in the short term,” said Michael Mina, an epidemiologist at the Harvard T.H. Chan School of Public Health. “Unless we’re going to let the virus run rampant again — but I think society has decided that is not an approach available to us.”
Unproven premise: The hopes for herd immunity — and for a vaccine — rest on the belief that the antibodies will protect against reinfection. There is some evidence suggesting that people do achieve immunity to the coronavirus, as they do with many other viruses. But it is not yet certain whether that’s true in all cases, or how robust the immunity may be, or how long it will last.
How big a risk do surfaces pose?
Groceries, packages, elevator buttons, doorknobs. Many people worry about touching all kinds of surfaces that others may have handled, for fear of infection. Should they?
To catch the virus that way, a series of things has to happen in just the right way. Droplets from an infected person’s sneeze or cough would have to get onto the surface; then you would have to touch it while enough virus particles remained viable; and then you would have to touch your eyes, nose or mouth.
Our Well editor Tara Parker-Pope explains that timing and quantity are important. The virus is fragile and begins to disintegrate within hours; though some particles can last up to three days on plastic or steel, there may not be enough left by then to infect you.
And you can break the chain of contamination completely with the pandemic’s golden rules: Wash your hands often, and avoid touching your face.
The New Yorkers still getting sick
After two months of stay-at-home restrictions, New York City has flattened its curve — but many people are still becoming infected. More than 13,000 people in the city tested positive for the virus in the last two weeks.
Epidemiologists, doctors, health officials and patients told him that the people catching the virus now in the New York area include essential workers and their families; elderly people; people who cannot socially distance at home; poor residents of the Bronx; and farm workers who live outside the city.
That’s who — but what about how? Andy said he did not find a complete answer for that, in part because the public health experts he spoke to were puzzled, too.
It’s a particularly difficult question, he told us, “because many people who get the virus don’t have any idea themselves how they got it.”
What you can do
Order food in safely. Takeout and delivery both pose little risk when you follow common-sense precautions. Contact the restaurant first to make sure workers wear masks and gloves, and eliminate touch points by skipping utensils and paying in advance.
Prepare for transformed air travel. If you fly this summer, bring hand sanitizer, wipes and a mask. Before you reach security, put items like wallets and phones in your carry-on, to reduce contact with the bins. Use the airline’s app for touch-free boarding.
Childproof your home. Accident risks loom larger when children are cooped up and parents are juggling work and caretaking. These tips will help you spot and reduce hazards indoors and out.
What you’re doing
I’m in quarantine in the basement for two weeks after traveling home from school. My mom and I like to sit at opposite ends of the staircase each night and play gin rummy with our own decks of cards. It helps pass the time, and it’s nice to feel like I’m engaging with someone without a screen, even if we’re far apart.
— Nicole McHenry, Seattle
Let us know how you’re dealing with the outbreak. Send us a response here, and we may feature it in an upcoming newsletter.