RSV and COVID-19 are not related. They are caused by two entirely different viruses from separate virus families, with distinct genetic structures, and they affect people differently. The confusion is understandable: both cause respiratory symptoms like cough, congestion, and difficulty breathing, and they circulate during overlapping times of year. But biologically, they have about as much in common as a cat and a goldfish.
Two Different Viruses With Similar Symptoms
RSV (respiratory syncytial virus) and SARS-CoV-2 (the virus that causes COVID-19) belong to completely different virus families. While both carry their genetic instructions in single-stranded RNA wrapped in an outer envelope, the similarities largely end there.
RSV has a relatively small genome of about 15,000 genetic letters encoding 11 proteins. SARS-CoV-2’s genome is twice that size, around 30,000 letters, encoding 29 proteins. They also read their genetic code in opposite directions: RSV uses negative-sense RNA, meaning it needs an extra step to translate its instructions, while SARS-CoV-2 uses positive-sense RNA that the host cell can read more directly. They use entirely different surface proteins to enter cells and spread through the body.
What links them in people’s minds is the overlap in symptoms. Cough, fever, nasal congestion, fatigue, and shortness of breath can show up with either infection. This overlap makes it impossible to tell them apart based on symptoms alone, which is why combination tests that check for RSV, COVID-19, and influenza from a single nasal swab have become a standard tool. These multiplex PCR tests can identify which virus is responsible in one run, reporting each target as either detected or not detected.
They Hit Different Age Groups Hardest
One of the clearest differences between these viruses is who they hit hardest. RSV is primarily dangerous for very young children and older adults. Globally, RSV causes an estimated 33.1 million respiratory infections in children under five each year, leading to roughly 3.2 million hospitalizations and about 59,600 in-hospital deaths in that age group. In a study of hospitalized children under 36 months, RSV infections required an average hospital stay of 8 days, compared to just 3 days for COVID-19. Children with RSV also needed bronchodilator therapy at far higher rates (88% versus about 6% for COVID).
COVID-19 flips that pattern. Children under four account for only about 3.9% of reported COVID-19 cases and 0.1% of deaths. The virus poses its greatest threat to older adults and people with chronic health conditions. While RSV can also be serious in older adults, the overall risk profile for each virus skews toward opposite ends of the age spectrum.
Different Seasonal Patterns
RSV and COVID-19 don’t follow the same calendar. CDC surveillance data from the 2024-2025 season shows RSV following a single, predictable winter peak, with positive test results hitting 11.0% during the week ending December 21, 2024. COVID-19, by contrast, showed a bimodal pattern with two separate waves: a summer peak of 17.9% positive tests in early August 2024, followed by a dip, and then a smaller winter peak of 6.7% in early January 2025.
This means your risk of catching each virus shifts at different times of year. RSV is overwhelmingly a winter virus, while COVID-19 can surge in summer months as well.
The Pandemic Changed RSV’s Behavior
One reason people associate these two viruses is that COVID-19 pandemic restrictions dramatically disrupted RSV’s normal patterns. During lockdowns, masking, and social distancing in 2020 and 2021, RSV nearly vanished. Young children who would normally have encountered RSV in their first or second winter simply didn’t. When restrictions lifted, RSV came roaring back in unusual off-season surges, hitting larger numbers of children who had no prior immune exposure. This created the impression that the two viruses were somehow connected, when in reality RSV was responding to the sudden removal of the same public health measures that had been suppressing all respiratory viruses.
Co-infection Is Uncommon
You can catch both viruses at the same time, but it doesn’t happen often. Clinical reviews have found RSV and SARS-CoV-2 co-infection rates averaging around 3%. Patients with both viruses tend to need slightly more supportive care in the hospital, but co-infection has not been linked to a higher risk of death compared to either virus alone.
Interestingly, animal research has suggested something counterintuitive: in mice, simultaneous infection with RSV and SARS-CoV-2 appeared to reduce the severity of COVID-19 symptoms and slow SARS-CoV-2 replication. Co-infected mice lost less body weight and showed lower illness scores than mice infected with SARS-CoV-2 alone. This may reflect a phenomenon called viral interference, where one respiratory virus triggers an immune response that partially blocks another, though the practical implications for humans are still being studied.
Separate Vaccines for Separate Viruses
Because these are unrelated viruses, protection against one does nothing for the other. Each requires its own vaccine.
RSV vaccines approved in the U.S. use protein subunit technology, delivering a piece of the virus’s surface protein to train the immune system. Two vaccines, Arexvy and Abrysvo, are available for older adults. Abrysvo can also be given during pregnancy to pass protective antibodies to newborns. For COVID-19, the primary vaccines in the U.S. use mRNA technology, which instructs cells to produce a piece of the spike protein and mount an immune response. Other COVID-19 vaccine types developed globally include viral vector, inactivated virus, and protein subunit approaches.
The timing and eligibility for each vaccine differ. RSV vaccines target older adults and, through maternal immunization, newborns. COVID-19 vaccines are recommended broadly across age groups, with updated formulations released to match circulating variants. Getting vaccinated against one virus provides no cross-protection against the other, so people in high-risk groups may benefit from both.