Human Metapneumovirus and RSV: How Their Seasons Shifted Around COVID-19, 2014–2024

Human metapneumovirus (hMPV) is a respiratory virus first identified as a cause of illness in 2001. It is a close relative of respiratory syncytial virus (RSV) — both belong to the Pneumoviridae family — and the two cause similar illnesses. Children, older adults and people with weakened immune systems are most at risk of hMPV-associated lower respiratory tract infections: bronchitis, bronchiolitis and pneumonia. hMPV can also make asthma and chronic obstructive pulmonary disease worse. Among U.S. adults, an estimated 12.1 hMPV-associated hospitalizations per 100,000 people occurred each year in 2016–2019.

There is an important difference between them: RSV now has vaccines and monoclonal antibody products that protect against severe disease, while hMPV has no licensed vaccine or antiviral treatment.

A CDC report looked at how the two viruses' seasons lined up before, during and after the COVID-19 pandemic.

How the data were gathered

The National Respiratory and Enteric Virus Surveillance System (NREVSS) collects weekly counts of tests and positive results from clinical, commercial and public health laboratories that report voluntarily. The analysis used PCR results from July 2014 to June 2024, from laboratories that reported consistently. A season begins at the first of at least two straight weeks with 3% or more of tests positive, ends at the last such week, and peaks in the week with the highest share of positives.

Weekly percentage of positive tests for RSV and hMPV, United States, July 2014–June 2024 (CDC).

Before the pandemic

• hMPV seasons typically began in early January, peaked in late March and ended in early June, lasting a median 21 weeks (range 15–25).
• RSV seasons typically began in late October, peaked in late December and ended in late April, lasting a median 26.5 weeks.
• The two overlapped heavily through winter: hMPV's season began a median 13.5 weeks before RSV's ended (range 11–19), and hMPV's peak came a median 11.5 weeks after RSV's (range 2–17).

What the pandemic changed

• 2020–21: hMPV circulation fell by 98%. Only 370 of 511,902 hMPV tests (0.07%) were positive, and neither virus crossed the 3% threshold that defines a season.
• 2021–22: an unusual hMPV season, peaking at very different times in different regions — from early December in some to early June in others — and lasting 35 weeks. RSV started in late May and peaked in late July.
• 2022–23 and 2023–24: hMPV returned to its familiar pattern, peaking in March and April. RSV seasons, however, kept ending early — in January in 2021–22 and 2022–23 and in March in 2023–24, instead of April.

The result was far less overlap. During and after the pandemic, the two seasons overlapped a median of 3 weeks (range 1–10), and hMPV's peak trailed RSV's by a median of 19 weeks (range 19–20) — 7.5 weeks more than before. In 2022–23 and 2023–24, most regions saw 0–4 weeks of overlap; the exceptions were HHS Region 6 (12 weeks) and Region 9 (6 weeks) in 2022–23.

Testing grew over the decade. The median number of hMPV tests reported per year rose 92%, from 476,169.5 before the pandemic to 914,660 during and after it, and the laboratories reporting hMPV results consistently went from 62 in 34 states (2014–15) to 122 in 38 states (2023–24).

Why the overlap matters

With RSV returning to its usual timing, CDC expected the two viruses to circulate together more in 2024–25 and later seasons. By the week ending March 22, 2025, they had already overlapped nationally for 5 weeks, with RSV at 4.4% and hMPV at 5.5% of tests positive. When they circulate together, the combined burden of illness could be higher than during the pandemic years, when they came separately — and a 2020 meta-analysis linked RSV–hMPV co-infections to higher odds of a child's admission to pediatric intensive care.

The viruses also affect children differently:

In older adults and people with weakened immune systems, the two cause severe disease in similar ways.

Knowing when the viruses circulate — and when they overlap — helps doctors decide when to test for which virus, helps hospitals prepare for surges, and helps public health officials catch outbreaks early.

Limits of the data

• The 3% threshold is an imprecise marker of a season, especially locally.
• Reporting is voluntary, the participating laboratories changed from year to year, and they may not represent every area. More laboratories and wider use of multi-virus test panels during COVID-19 likely found hMPV cases that would once have gone undiagnosed.
• NREVSS collects no patient details, so the share of tests done on children versus adults is unknown.

Sources

• Jobe NB, Rose E, Winn AK, Goldstein L, Schneider ZD, Silk BJ. "Human Metapneumovirus Seasonality and Co-Circulation with Respiratory Syncytial Virus — United States, 2014–2024," MMWR Vol. 74, No. 11, CDC; a work of the United States government in the public domain.