A new study offers the first physical evidence that the coronavirus was circulating at low levels in New York City as early as the first week of February.
The city confirmed its first infection on March 1. Mathematical models have predicted that the virus was making its way through the city weeks before then, but the new report is the first to back the conjecture with testing data.
The study found that some New Yorkers had antibodies to the virus as early as the week ending Feb. 23. Given the time needed to produce antibodies, those people were most likely infected with the virus about two weeks earlier.
“You’re probably talking about very early in February,” said Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai, who led the study. “It looks like there was at least low-level circulation.”
The findings were posted online Tuesday and have not yet been vetted by other scientists in a formal review, but several experts said the work was rigorous and credible, if not entirely surprising.
Genetic analyses have suggested that the virus entered the city several times early in the year, but most of those introductions died out and did not initiate the city’s epidemic.
“If I had to put a single date on it, based on current models, we had it as Feb. 19 as the arrival that fueled things,” said Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle. Dr. Krammer’s date is only slightly earlier, he noted.
The study also confirms estimates by epidemiologists working for New York State that roughly one in five New Yorkers had been exposed to the virus by late April, a figure broadly consistent with data released on Friday by the Centers for Disease Control and Prevention.
“I think it’s cool that we all have similar numbers,” Dr. Krammer said.
The similarity is even more striking, experts said, because the three studies all arrived at their estimates differently.
Dr. Krammer and his colleagues analyzed plasma samples from nearly 5,500 patients who went to Mount Sinai for routine medical appointments, were seen in its emergency department or were hospitalized from the week ending Feb. 9 through the week ending April 19.
The C.D.C. looked at blood samples from people who went in for routine medical exams, but only the week ending April 1 for New York City. The New York State study recruited people at supermarkets from April 19 to April 28.
“When we have three sources all giving you consistent results, that lends strength to all the findings,” said Eli Rosenberg, an epidemiologist at the State University of New York at Albany and lead author of the state study.
The numbers from all three studies also agree on a crucial point: The vast majority of infections in New York City and elsewhere in the country went undiagnosed. Even in places with large outbreaks, the number of people exposed to the virus is still far from what is needed for herd immunity.
The Mount Sinai researchers grouped their samples in different ways and analyzed them using a lab-based antibody test that is highly accurate and specific to the new coronavirus.
Among people admitted to the emergency room or the hospital during the study period, the prevalence of antibodies rose to nearly 60 percent from 3.2 percent, the researchers found. These numbers are high because they include people who were severely ill with the coronavirus.
But among people who gave blood for routine appointments, or were admitted to the hospitals for reasons unrelated to the coronavirus — a group that represents the general population — fewer than 2 percent of people had antibodies until the week ending March 29. The rate rose exponentially after that, ending at 19.3 percent among patients seen in the week ending April 19.
The team broke this latter group down further by the reason for their appointment, and found the increase in prevalence was mostly driven by pregnant women. Nearly one in 10 pregnant women had antibodies to the virus by the week of March 29, and the number rose steadily to nearly 27 percent by the week ending April 19.
Frequently Asked Questions and Advice
Updated June 30, 2020
What are the symptoms of coronavirus?
Common symptoms include fever, a dry cough, fatigue and difficulty breathing or shortness of breath. Some of these symptoms overlap with those of the flu, making detection difficult, but runny noses and stuffy sinuses are less common. The C.D.C. has also added chills, muscle pain, sore throat, headache and a new loss of the sense of taste or smell as symptoms to look out for. Most people fall ill five to seven days after exposure, but symptoms may appear in as few as two days or as many as 14 days.
What’s the best material for a mask?
Scientists around the country have tried to identify everyday materials that do a good job of filtering microscopic particles. In recent tests, HEPA furnace filters scored high, as did vacuum cleaner bags, fabric similar to flannel pajamas and those of 600-count pillowcases. Other materials tested included layered coffee filters and scarves and bandannas. These scored lower, but still captured a small percentage of particles.
Is it harder to exercise while wearing a mask?
A commentary published this month on the website of the British Journal of Sports Medicine points out that covering your face during exercise “comes with issues of potential breathing restriction and discomfort” and requires “balancing benefits versus possible adverse events.” Masks do alter exercise, says Cedric X. Bryant, the president and chief science officer of the American Council on Exercise, a nonprofit organization that funds exercise research and certifies fitness professionals. “In my personal experience,” he says, “heart rates are higher at the same relative intensity when you wear a mask.” Some people also could experience lightheadedness during familiar workouts while masked, says Len Kravitz, a professor of exercise science at the University of New Mexico.
I’ve heard about a treatment called dexamethasone. Does it work?
The steroid, dexamethasone, is the first treatment shown to reduce mortality in severely ill patients, according to scientists in Britain. The drug appears to reduce inflammation caused by the immune system, protecting the tissues. In the study, dexamethasone reduced deaths of patients on ventilators by one-third, and deaths of patients on oxygen by one-fifth.
What is pandemic paid leave?
The coronavirus emergency relief package gives many American workers paid leave if they need to take time off because of the virus. It gives qualified workers two weeks of paid sick leave if they are ill, quarantined or seeking diagnosis or preventive care for coronavirus, or if they are caring for sick family members. It gives 12 weeks of paid leave to people caring for children whose schools are closed or whose child care provider is unavailable because of the coronavirus. It is the first time the United States has had widespread federally mandated paid leave, and includes people who don’t typically get such benefits, like part-time and gig economy workers. But the measure excludes at least half of private-sector workers, including those at the country’s largest employers, and gives small employers significant leeway to deny leave.
Does asymptomatic transmission of Covid-19 happen?
So far, the evidence seems to show it does. A widely cited paper published in April suggests that people are most infectious about two days before the onset of coronavirus symptoms and estimated that 44 percent of new infections were a result of transmission from people who were not yet showing symptoms. Recently, a top expert at the World Health Organization stated that transmission of the coronavirus by people who did not have symptoms was “very rare,” but she later walked back that statement.
What’s the risk of catching coronavirus from a surface?
Touching contaminated objects and then infecting ourselves with the germs is not typically how the virus spreads. But it can happen. A number of studies of flu, rhinovirus, coronavirus and other microbes have shown that respiratory illnesses, including the new coronavirus, can spread by touching contaminated surfaces, particularly in places like day care centers, offices and hospitals. But a long chain of events has to happen for the disease to spread that way. The best way to protect yourself from coronavirus — whether it’s surface transmission or close human contact — is still social distancing, washing your hands, not touching your face and wearing masks.
How does blood type influence coronavirus?
A study by European scientists is the first to document a strong statistical link between genetic variations and Covid-19, the illness caused by the coronavirus. Having Type A blood was linked to a 50 percent increase in the likelihood that a patient would need to get oxygen or to go on a ventilator, according to the new study.
How many people have lost their jobs due to coronavirus in the U.S.?
The unemployment rate fell to 13.3 percent in May, the Labor Department said on June 5, an unexpected improvement in the nation’s job market as hiring rebounded faster than economists expected. Economists had forecast the unemployment rate to increase to as much as 20 percent, after it hit 14.7 percent in April, which was the highest since the government began keeping official statistics after World War II. But the unemployment rate dipped instead, with employers adding 2.5 million jobs, after more than 20 million jobs were lost in April.
How can I protect myself while flying?
If air travel is unavoidable, there are some steps you can take to protect yourself. Most important: Wash your hands often, and stop touching your face. If possible, choose a window seat. A study from Emory University found that during flu season, the safest place to sit on a plane is by a window, as people sitting in window seats had less contact with potentially sick people. Disinfect hard surfaces. When you get to your seat and your hands are clean, use disinfecting wipes to clean the hard surfaces at your seat like the head and arm rest, the seatbelt buckle, the remote, screen, seat back pocket and the tray table. If the seat is hard and nonporous or leather or pleather, you can wipe that down, too. (Using wipes on upholstered seats could lead to a wet seat and spreading of germs rather than killing them.)
What should I do if I feel sick?
If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor. They should give you advice on whether you should be tested, how to get tested, and how to seek medical treatment without potentially infecting or exposing others.
By comparison, people who came in for appointments related to surgery, cancer or cardiology plateaued at about 9 percent.
Subgroup analyses tend not to be reliable because of the smaller sample sizes, but this is a large study and the trends are intriguing, said Taia Wang, an immunologist at Stanford University.
“It does suggest the possibility that different groups of patients might have different susceptibility to SARS-CoV-2 infection,” she said.
Experts were also struck by the relatively flat prevalence of coronavirus antibodies in blood samples from the first few weeks.
“I would expect during this time period, where people are not modifying their behavior, you’d get much closer to exponential growth,” Dr. Bedford said.
Other cities, like San Francisco, have similarly shown periods when the virus seemed to percolate until something — perhaps a superspreader event — triggered an exponential rise in infections.
“We’ve seen this elsewhere repeatedly, and it’s still strange to me,” Dr. Bedford said.
Dr. Krammer is continuing to track antibodies in blood samples and plans to do so for at least a year. But he said he would not expect the prevalence to rise much above 20 percent in May or June, because infections in New York City had tapered off by then.