Two papers published Friday in the journal the Lancet offer some of the first rigorous analyses of patients who contracted a novel coronavirus that has broken out in China and spread to other countries. Among their discoveries: The virus does not only affect people with other, underlying health conditions, and people who are not showing symptoms can still be carrying the virus.

In one study, researchers analyzed data from the first 41 patients who were admitted to hospitals with confirmed cases of the infection in the central Chinese city of Wuhan, where the outbreak is believed to have originated last month. Two-thirds had been to a large seafood market that also sold wild animals for meat and is thought to be where the virus jumped from an animal source to people. The median age of the patients was 49.

The patients displayed a wide range of symptoms, many of which were similar to those caused by SARS, another coronavirus, which caused a global outbreak in 2002-2003 that started in China. All of them had pneumonia, and most had fever and cough. Some people had fatigue; rarer symptoms included headache and diarrhea. The researchers noted that patients with SARS more frequently had runny noses, sore throats, and diarrhea than those with the novel coronavirus, which is provisionally being called 2019-nCoV.

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One key finding: It’s not only people with other health conditions that are getting sick, the researchers reported. Some of the fatal cases caused by the virus have been among people with underlying diseases like diabetes, liver disease, and hypertension, but the majority of the first 41 patients infected with the disease in Wuhan were healthy. The researchers noted that SARS infections similarly did not only affect people with other conditions.

About a third of the 41 patients needed intensive care, and six of them died. Some of the patients with more serious illnesses suffered from a dangerous immune system overreaction called a cytokine storm, but the researchers said they still did not have a good understanding of how the virus affects the immune system.

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As of Friday, there were more than 830 cases of the coronavirus infection in China, with 25 deaths, and a handful of cases in places — including Thailand, Japan, South Korea, and the United States — that were in people who traveled to those countries from China.

The second paper focused on one family who came down with pneumonia in Shenzhen. Five family members had recently traveled to Wuhan and had the virus, as did one relative who had not traveled to Wuhan.

So far, authorities have only confirmed human-to-human transmission of the virus among families and in health care clinics — settings where people are likely to be in close contact with each other, according to the World Health Organization. This appears to be the case with the family that was studied. Still, health officials do not know exactly how efficiently the virus can pass among people.

One child with the virus did not show any symptoms. Health authorities have said that people with the virus have shown a range of symptoms, from very mild to very severe. But an asymptomatic infection raises the question of whether people have to be showing signs of the disease to pass it to people, a question that experts are rushing to answer.

“Because asymptomatic infection appears possible, controlling the epidemic will also rely on isolating patients, tracing and quarantining contacts as early as possible, educating the public on both food and personal hygiene, and ensuring health care workers comply with infection control,” Dr. Kwok-Yung Yuen from the University of Hong Kong-Shenzhen Hospital, who led the research, said in a statement.

In a commentary piece also published Friday by the Lancet, Dr. David Heymann, an infectious disease epidemiologist at the London School of Hygiene and Tropical Medicine, wrote that “the picture these two manuscripts paint is of a disease with a 3-6 day incubation period and insidious onset.”

The researchers who wrote the two papers and other experts cautioned that these were small studies with limited numbers of patients in a rapidly evolving outbreak. But they noted that sharing information like this as quickly and rigorously as possible can help shape the response.

“The information in these articles are pieces of the jigsaw puzzle that are being fit together by WHO as it continues to collect official reports and informal information from its virtual groups of national clinicians, epidemiologists, and virologists working at outbreak sites and brought together from around the world,” Heymann wrote. “When pieced together, these emerging data will permit regular refinement of the risk assessment, and real-time guidance to countries for patient management and outbreak control, including the best case definition for use in surveillance around outbreak sites and elsewhere.”