Reports of a surge in respiratory disease cases in China have brought grim echoes of the start of the Covid-19 pandemic almost exactly five years ago.

But despite the superficial similarities, the situation is very different and far less worrisome, medical experts say.

The Chinese cases are reportedly infections with the human metapneumovirus, known to doctors as HMPV. Here’s what we know so far:

What is HMPV?

It is one of several pathogens that circulate worldwide each year and cause respiratory diseases. HMPV is widespread – so common that most people become infected in childhood and can experience multiple infections throughout their lives. In countries with months of cold weather, HMPV can have an annual season, similar to the flu, while in places closer to the equator it circulates in lower levels year-round.

HMPV is similar to a virus better known in the United States – respiratory syncytial virus, or RSV. It causes symptoms similar to those of flu and Covid, including cough, fever, nasal congestion and wheezing.

Most HMPV infections are mild and resemble bouts of the common cold. However, in severe cases, bronchitis or pneumonia can occur, especially in infants, older adults, and immunocompromised people. Patients with pre-existing lung diseases 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; Deaths are more common in lower-income countries with weak health systems and poor surveillance.

How long has this virus been around?

The virus was identified in 2001, but researchers say it has been circulating in humans for at least 60 years. While it’s not new, it doesn’t have the notoriety of influenza, Covid or even RSV, Dr. Leigh Howard, associate professor of pediatric infectious diseases at Vanderbilt University Medical Center.

One reason is that it is rarely spoken of by name, except when people are hospitalized with a confirmed case of it.

“The clinical features are really difficult to distinguish from other viral diseases and we don’t routinely test for HMPV like we do for Covid, flu or RSV,” said Dr. Howard. “Therefore, most infections remain undetected and are attributed to respiratory diseases.”

How does a person become infected with HMPV?

The virus spreads primarily through droplets or aerosols when coughing or sneezing, through direct contact with an infected person, or through contact with contaminated surfaces – basically the same way people get colds, flu and Covid.

Is there a vaccine? Or a treatment?

There is no vaccine against HMPV. However, there is a vaccine against RSV and research is currently underway to develop a vaccine that could protect against both viruses with one shot because they are similar. There is no specific antiviral treatment for HMPV; Treatment focuses on managing the symptoms.

What does China say about this?

Chinese authorities have acknowledged that HMPV cases are increasing, but stressed that the virus is a known condition and does not pose a major problem. 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 at the Chinese Center for Disease Control and Prevention on Dec. 27, Kan Biao, director of the center’s Institute of Infectious Diseases, said HMPV cases are increasing among children ages 14 and younger. The increase is particularly notable in northern China, he said. Influenza cases have also increased, he said.

Cases could increase during the Lunar New Year holiday in late January, when many people travel and gather in large groups, he said.

But overall, Mr. Kan said, “the scale and intensity of the spread of respiratory infectious diseases this year will be lower than last year given the current situation.”

Official Chinese data shows that HMPV cases have increased in both outpatient and emergency cases since mid-December, according to Xinhua, the state news agency. Some parents and social media users were unfamiliar with the virus and sought advice online, the outlet said. It called for calm and normal precautions such as washing hands frequently and avoiding crowded places.

In a routine media briefing Friday, a State Department spokesman reiterated that cases of influenza and other respiratory viruses routinely increase this time of year, but that they “appear to be less severe and spreading at a lower rate compared to last year.” .”

Chinese officials said last week they would set up a surveillance system for pneumonia of unknown cause. It will include procedures for laboratories to report cases and for disease control and prevention agencies to screen and treat cases, state broadcaster CCTV reported.

What was the public reaction in China?

Online, state media tried to reassure people by warning them against blindly taking antiviral drugs, while people said they had never heard of HMPV and expressed concern that it was a new pathogen.

Some users have joked, saying they could finally use up the masks they had been hoarding during the coronavirus pandemic. Many commentators have discussed a general rise in illness rates, 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 WHO has not expressed any concerns. Dr. Margaret Harris, a spokeswoman for the organization, cited weekly reports from Chinese authorities that showed a predictable increase in cases.

“As would be expected for this time of year, winter in the Northern Hemisphere, there is a month-over-month increase in acute respiratory infections, including seasonal influenza, RSV and human metapneumovirus,” she said by email.

Should I be worried?

The reports from China are reminiscent of the first, confusing days of the Covid pandemic, and the WHO is still calling on China to provide more information about the origins of this outbreak five years later.

But the current situation is different in key respects. Covid was a virus that spread from animals to humans and was previously unknown. HMPV is well researched and there are extensive options for testing it. There is broad population-level immunity to this virus worldwide; 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 crucial for China to share its data on this outbreak in a timely manner,” said Dr. Sanjaya Senanayake, infectious disease specialist and associate professor of medicine at the Australian National University. “This includes epidemiological data about who is becoming infected. “We also need genomic data that confirms that HMPV is the culprit and that there are no significant mutations of concern.”

Vivian Wang contributed to reporting from Beijing.