Harry Henri, a research assistant, working with blood samples from coronavirus patients at SUNY Downstate’s BioBank in Brooklyn.Credit...Misha Friedman for The New York Times
When experts recommend wearing masks, staying at least six feet away from others, washing your hands frequently and avoiding crowded spaces, what they’re really saying is: Try to minimize the amount of virus you encounter.
A few viral particles cannot make you sick — the immune system would vanquish the intruders before they could. But how much virus is needed for an infection to take root? What is the minimum effective dose?
A precise answer is impossible, because it’s difficult to capture the moment of infection. Scientists are studying ferrets, hamsters and mice for clues but, of course, it wouldn’t be ethical for scientists to expose people to different doses of the coronavirus, as they do with milder cold viruses.
“The truth is, we really just don’t know,” said Angela Rasmussen, a virologist at Columbia University in New York. “I don’t think we can make anything better than an educated guess.”
Common respiratory viruses, like influenza and other coronaviruses, should offer some insight. But researchers have found little consistency.
For SARS, also a coronavirus, the estimated infective dose is just a few hundred particles. For MERS, the infective dose is much higher, on the order of thousands of particles.
The new coronavirus, SARS-CoV-2, is more similar to the SARS virus and, therefore, the infectious dose may be hundreds of particles, Dr. Rasmussen said.
But the virus has a habit of defying predictions.
Generally, people who harbor high levels of pathogens — whether from
Some people are generous transmitters of the coronavirus; others are stingy. So-called super-spreaders seem to be particularly gifted in transmitting it, although it’s unclear whether that’s because of their biology or their behavior.
On the receiving end, the shape of a person’s nostrils and the amount of nose hair and mucus present — as well as the distribution of certain cellular receptors in the airway that the virus needs to latch on to — can all influence how much virus it takes to become infected.
A higher dose is clearly worse, though, and that may explain why some young health care workers have fallen victim even though the virus usually targets older people.
The crucial dose may also vary depending on whether it’s ingested or inhaled.
People may take in virus by touching a contaminated surface and then putting their hands on their nose or mouth. But “this isn’t thought to be the main way the virus spreads,” according to the Centers for Disease Control and Prevention.
and even heavy breathing can result in the expulsion of thousands of large and small respiratory droplets carrying the virus.
“It’s clear that one doesn’t have to be sick and coughing and sneezing for transmission to occur,” said Dr. Dan Barouch, a viral immunologist at Beth Israel Deaconess Medical Center in Boston.
Larger droplets are heavy and float down quickly — unless there’s a breeze or an air-conditioning blast — and can’t penetrate surgical masks. But droplets less than 5 microns in diameter, called aerosols, can linger in the air for hours.
“They travel further, last longer and have the potential of more spread than the large droplets,” Dr. Barouch said.
The Coronavirus Outbreak Today’s Question: How do we start exercising again without hurting ourselves after months of lockdown?
Exercise researchers and physicians have some blunt advice for those of us aiming to return to regular exercise now:
American adults tended to be about 12 percent less active after the stay-at-home mandates began in March than they were in January. But there are steps you can take to ease your way back into regular exercise safely. First, “start at no more than 50 percent of the exercise you were doing before Covid,” says Dr. Monica Rho, the chief of musculoskeletal medicine at the Shirley Ryan AbilityLab in Chicago. Thread in some preparatory squats, too, she advises. “When you haven’t been exercising, you lose muscle mass.” Expect some muscle twinges after these preliminary, post-lockdown sessions, especially a day or two later. But sudden or increasing pain during exercise is a clarion call to stop and return home.
Three factors seem to be particularly important for aerosol transmission: proximity to the infected person, air flow and timing.
A windowless public bathroom with high foot traffic is riskier than a bathroom with a window, or a bathroom that’s rarely used. A short outdoor conversation with a masked neighbor is much safer than either of those scenarios.
Recently, Dutch researchers used a special spray nozzle to simulate the expulsion of saliva droplets and then tracked their movement. The scientists found that just cracking open a door or a window
than in airier patient rooms or crowded public areas.
This makes intuitive sense, experts said. But they noted that aerosols, because they are smaller than 5 microns, would also contain much less, perhaps millions-fold less, virus than droplets of 500 microns.
“It really takes a lot of these single-digit size droplets to change the risk for you,” said Dr. Joshua Rabinowitz, a quantitative biologist at Princeton University.
Apart from avoiding crowded indoor spaces, the most effective thing people can do is wear masks, all of the experts said. Even if masks don’t fully shield you from droplets loaded with virus, they can cut down the amount you receive, and perhaps bring it below the infectious dose.
“This is not a virus for which hand washing seems like it will be enough,” Dr. Rabinowitz said. “We have to limit crowds, we have to wear masks.”
In the mid-1970s we took a trip back to our home town, Buffalo, New York. Somebody had been rearranging the scenery. First, I missed the arching elm trees that were wiped out by Dutch Elm Disease. Those DAMN Dutch! Buffalo without the majestic elms was like seeing your grandmother in her underwear. There were little new trees being held up by sticks and wire. I hoped I would live long enough to see them full grown.
We were driving our motor home and stayed at a KOA on Grand Island, a big chunk of land in the Niagara River that was rural in my childhood, but was now looking suburban. The temperature was in the low 40's, and the wind across the island was fierce.
Accompanied by my old buddy Bob Egan and his girlfriend Mary Lou, we made the rounds of the nightspots and dayspots.
I noticed that people had an obsession with "improving" pianos. Most of the grand old upright pianos had been cut down in an attempt to make them into spinets. It didn't work. The shape always came out sort of hunchbacked. They stuck to it, though, painting them with pink or white enamel, and putting mirrors over the keys. I could never play a piano with mirrors over the keys. I can't stop watching the hands in the mirror. It's like trying to talk with an echo on the telephone line.
Each night we started out at a Grand Island tavern built into the downstairs floor of an old house. The large screened porch covering the front of the building had storm windows up. It was late autumn, and no place for sissies. The Roast Beef sandwiches on Weck, a Buffalo specialty, were perfect. That's about all I ate while in town.
The tavern had an old upright piano, that was a bit out of tune and was missing some ivories. It looked as though it needed some Ragtime, so we played some every night.
We also went to Dinty Moore's Restaurant at Elmwood and Kenmore Avenues, where they had a piano bar and a dance floor. Misty danced with Bob, who looked funny in my huge brimmed cowboy hat. That's the first time we've been bar hopping in a 38 foot motorhome.
In the daylight, we took in Delaware Park, the zoo, the houses where we used to live, some old landmarks All things wood must be covered with Formica, and a big picture window must be gouged out of every house front. Crinkly shingles of various colors were tacked on to houses I used to like. The solid wood counter on the upstairs porch was now wrought iron railing. Satellite TV dishes pop out of the wall like giant toadstools, and our wonderful sunporch was replaced by the mandatory picture window.
Before we said goodby, we had a couple of get-togethers in a North Tonawanda tavern, played music, and had fun. Most of those friends and relatives are gone now, but we still see them in our memories of that visit, and in the fading snapshots that were taken.
I learned something... It's not so much the the way it looks, or the economic situation, or even the great food It's the feeling... the aura, that makes Buffalo unique. The soul, the energy, and the personality are still there.
LATER: In 2010 We visited Buffalo again and found it better than ever. Many of our old haunts had ignored time and were the same, but with new people. There were new improvements and the city looked great. Buffalo has its unique energy and personality. We'd love to visit again sometime, but we don't live there anymore.