What We Know About HMPV, the Virus Spreading in China

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:

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.