Reports of a surge in cases of a respiratory virus in China have evoked dark echoes of the start of the Covid-19 pandemic almost exactly five years ago.
But despite the surface similarities, this situation is very different, and far less worrisome, medical experts say.
The Chinese cases are reported to be infections with human metapneumovirus, known to doctors as HMPV. Here is what we know so far:
What is HMPV?
It is one of several pathogens that circulate across the world each year, causing respiratory illnesses. HMPV is common — so common that most people will be infected while they are still children and may experience several infections in their lifetimes. In countries with months of cold weather HMPV can have an annual season, much like the flu, while in places closer to the Equator it circulates at lower levels all year long.
HMPV is similar to a virus that is better known in the United States — respiratory syncytial virus, or R.S.V. It causes symptoms much like those associated with flu and Covid, including cough, fever, nasal congestion and wheezing.
Most HMPV infections are mild, resembling bouts of the common cold. But severe cases can result in bronchitis or pneumonia, particularly among infants, older adults and immunocompromised people. Patients with pre-existing lung conditions, such as asthma, chronic obstructive pulmonary disease or emphysema, are at higher risk of severe outcomes.
In higher-income countries, the virus is rarely fatal; in lower-income countries, with weak health systems and poor surveillance, deaths are more common.
How long has this virus been around?
The virus was identified in 2001, but researchers say it has circulated in humans for at least 60 years. Though it is not new, it doesn’t have the name recognition of influenza, Covid or even R.S.V., said Dr. Leigh Howard, an associate professor of pediatric infectious disease at Vanderbilt University Medical Center.
One reason is that it is rarely discussed by name, except when people are hospitalized with a confirmed case of it.
“The clinical features are really difficult to distinguish from other viral illnesses, and we don’t routinely test for HMPV the way we do for Covid, flu or R.S.V.,” Dr. Howard said. “So most infections go unrecognized and are chalked up to whatever respiratory thing is going around.”
How does a person get infected with HMPV?
The virus spreads primarily through droplets or aerosols from coughing or sneezing, through direct contact with an infected individual or through exposure to contaminated surfaces — basically the same ways people get colds, flu and Covid.
Is there a vaccine? Or a treatment?
There is no vaccine against HMPV. But there is a vaccine for R.S.V., and research is underway to find a vaccination that could protect against both viruses with one shot, since they are similar. There is no antiviral treatment specifically for HMPV; treatment focuses on management of symptoms.
What is China saying about it?
The Chinese authorities have acknowledged that HMPV cases are increasing, but have emphasized that the virus is a known entity and is not a major concern. The coronavirus that causes Covid-19 was a new pathogen, so people’s immune systems had not built up defenses against it.
At a news conference held by China’s Center for Disease Control and Prevention on Dec. 27, Kan Biao, the director of the center’s Institute for Infectious Diseases, said that HMPV cases were rising among children 14 years and younger. The increase was especially notable in northern China, he said. Influenza cases have also increased, he said.
Cases could spike during the Lunar New Year holiday, at the end of January, when many people travel and gather in large groups, he said.
But overall, Mr. Kan said, “judging from the current situation, the scale and intensity of the spread of respiratory infectious diseases this year will be lower than last year’s.”
Official Chinese data shows that HMPV cases have been rising since mid-December, in both outpatient and emergency cases, according to Xinhua, the state news agency. Some parents and social media users were unfamiliar with the virus and were seeking advice online, the outlet said; it urged calm and ordinary precautions such as washing one’s hands frequently and avoiding crowded places.
In a routine media briefing on Friday, a spokesperson for the Foreign Ministry reiterated that cases of influenza and other respiratory viruses routinely increase at this time of year but that they “appear to be less severe and spread on a smaller scale compared with the previous year.”
Chinese officials said last week that it would set up a monitoring system for pneumonia of unknown origin. It will include procedures for laboratories to report cases and for disease control and prevention agencies to verify and handle them, the state broadcaster CCTV reported.
What has the public response in China been?
Online, amid comments from people saying they had never heard of HMPV and expressing concern that it was a new pathogen, state media outlets have sought to reassure people, warning them against blindly taking antiviral medications.
Some users have cracked jokes, saying that they could finally use up the masks they had stockpiled during the coronavirus pandemic. Many commenters have discussed a general uptick in illness, not just HMPV: “Why does the flu hurt so much” was trending on Weibo, a social media platform, on Monday.
What does the World Health Organization say?
The W.H.O. has not expressed concern. Dr. Margaret Harris, a spokeswoman for the organization, cited weekly reports from the Chinese authorities that showed a predictable rise in cases.
“As expected for this time of year, the Northern Hemisphere winter, there is a month-over-month increase of acute respiratory infections, including seasonal influenza, R.S.V. and human metapneumovirus,” she said by email.
Should I worry?
The reports coming from China are evocative of those from the first, confusing days of the Covid pandemic, and the W.H.O. is still urging China to share more information about the origin of that outbreak, five years on.
But the current situation is different in key respects. Covid was a virus that spilled over into humans from animals and was previously unknown. HMPV is well studied, and there is widespread capacity to test for it. There is broad population-level immunity to this virus globally; there was none, for Covid. A severe HMPV season can strain hospital capacity — particularly pediatric wards — but does not overwhelm medical centers.
“However, it is also vital for China to share its data on this outbreak in a timely manner,” said Dr. Sanjaya Senanayake, a specialist in infectious diseases and associate professor of medicine at the Australian National University. “This includes epidemiologic data about who is getting infected. Also, we will need genomic data confirming that HMPV is the culprit, and that there aren’t any significant mutations of concern.”
Vivian Wang contributed reporting from Beijing.
