The virus that causes Covid-19 was present in New York City weeks before the first confirmed case of the disease, infecting more than 1.7m New Yorkers and killing them at a rate 10 times greater than flu, a new research paper has shown.

Researchers have discovered antibodies to the virus in samples in February as part of a study of more than 10,000 plasma samples conducted at Mount Sinai, the New York-based hospital system, and published in a peer-reviewed paper in the science journal Nature on Tuesday.

New York — whose initial response to the virus was hampered by a lack of access to tests — identified its first confirmed case on March 1. But the study suggested it could have been circulating in early February.

While the virus was circulating, the samples sat in the lab. Researchers did not begin to analyse the samples until mid-March, using tests that were only designed for research purposes.

Most of the samples were taken from people who came to the hospital for other reasons — from pregnancy to cancer. They were compared with samples from a control group of people who sought urgent care, often for Covid-19. The samples were taken from February 9.

Emilia Mia Sordillo, director of clinical microbiology at Mount Sinai and a senior author on the study, said: “We now know there were many asymptomatic and mild to moderate cases that likely went undetected.”

Florian Krammer, a professor of microbiology at Mount Sinai who co-authored the study, said the findings confirm an analysis of the virus’ genome that suggested that Sars-Cov-2 appeared in New York in February. The initial findings from the Mount Sinai study were published in June, before being peer-reviewed. 

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The study calculated that about 1 in 100 infected people died from Covid-19. Dr Krammer said this was a “very high infection fatality rate” in its first wave, higher than many other parts of the world. The mortality rate is likely to come down as more is learnt about treating the disease, but Dr Krammer warned that it could rise as hospitals get flooded with patients.

“The virus needs to be taken seriously. If we get too many cases in a healthcare system, it becomes overwhelmed,” he said. 

The paper also found robust antibody responses that lasted for several months after people were infected, appearing to contradict a study from Imperial College London that found the proportion of Brits with antibodies declined over the summer. 

Dr Krammer said the UK study had been “over-interpreted” and caused “panic”. He said that his team found there had been no decline, after looking at the levels of antibodies in samples taken every week from February to July.

The Nature study suggested that a fifth of the New York population showed antibodies for the disease. While that could slow the spread of the virus, it was not close to the proportion required for community immunity, Dr Krammer said.

So far more than 223,000 people have died from the virus in the US, according to Covid Tracking Project data.

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Via Financial Times