RSV infection linked to more heart problems in the following year

The background: a common virus with a heavy toll in older adults

RSV infection has only recently been recognised as common among adults. In older adults, especially those with chronic conditions, it can lead to pneumonia, hospital admission and death, with an overall burden comparable to that of seasonal flu^[1].

Doctors have long known that acute respiratory infections can act as short-term triggers for heart attacks and strokes. A Scottish study of national records, for example, found that the rate of a first heart attack was around five to six times higher than usual in the first three days after a laboratory-confirmed respiratory virus infection, with the raised risk lasting about a week^[2]. In the United States, a surveillance study of more than 6,000 adults aged 50 and over who were in hospital with RSV found that 22% had an acute cardiac event during their stay, most often acute heart failure – 33% of those with existing heart disease and 8.5% of those without^[3]. That study had no comparison group, so it could not say how many of these events were due to the infection^[1,3].

What was largely missing, according to the Danish authors, was a clear estimate of the absolute extra burden – how many additional heart and circulation problems occur per 100 infected people – and of whether the risk persists beyond the first weeks. Such numbers have become more important since several RSV vaccines for older adults were licensed in recent years^[1].

What the researchers did

Denmark gives every resident a personal identification number that links national health records. Researchers at Statens Serum Institut, a Danish government institute, used these registries to identify all residents aged 45 or older (about 2.6 million people) and found 8,825 who had a first positive RSV test between January 2019 and December 2024. All infections were confirmed by laboratory PCR tests^[1].

For 8,747 of them (99.1%), the researchers found a “twin” without a positive RSV test on that day: a person of the same sex and five-year age group, with the same set of pre-existing conditions such as heart disease, diabetes, chronic lung disease, kidney disease or cancer. The 17,494 people in the study were on average 72 years old, and 58% were women. Each pair was followed for up to one year^[1].

The main outcomes were hospital diagnoses of cardiovascular disease: coronary heart disease (including heart attacks), stroke and heart failure – together called “major adverse cardiovascular events” – plus arrhythmias, blood clots in the veins and inflammation of the heart, which together made up “any cardiovascular event”. The researchers reported the results as risk differences: the extra percentage of people with an event in the RSV group compared with their matched partners^[1].

To put the numbers in context, they also compared people with RSV with people who had flu, a hip fracture or a urinary tract infection. And as a plausibility check, they tested whether RSV was linked to an outcome it should have nothing to do with – a hip fracture^[1].

What they found

About five extra events per 100 people. Over one year, 665 cardiovascular events were recorded among people with RSV and 257 among those without. The risk difference was 4.69 percentage points; taking statistical uncertainty into account, the true value is likely to lie between 4.0 and 5.4 extra events per 100 people. For the narrower group of major events (coronary heart disease, stroke, heart failure), the difference was 2.37 per 100^[1].

Most of it early, some of it later. Within the first 30 days, the difference was already 3.82 per 100 – roughly four-fifths of the one-year total. After that, the gap continued to widen slowly for the rest of the year^[1].

Mainly rhythm problems and heart failure. Arrhythmias made up the largest share (2.81 extra per 100 after one year), followed by heart failure (1.33 per 100). The excess was much smaller for stroke (0.49 per 100) and coronary heart disease (0.36 per 100), and there was no difference for inflammation of the heart^[1].

Who was most affected. The risk depended strongly on age: the one-year difference was 0.91 per 100 in people aged 45 to 54, but 7.93 per 100 in those aged 85 to 94. In people who already had cardiovascular disease, it was 11.95 per 100, and in people with diabetes 7.50 per 100. People without any of the recorded pre-existing conditions still had an excess of 3.14 per 100. Among people admitted to hospital with RSV – 69% of all those infected – the difference was 6.61 per 100, while people with RSV who were not admitted showed no measurable excess^[1].

Similar to flu, lower than a hip fracture. When people with RSV were compared directly with people who had flu, there was no significant difference in cardiovascular events over the year. People with a hip fracture or a urinary tract infection, however, had somewhat more cardiovascular events than people with RSV^[1]. The plausibility check worked as intended: RSV was not linked to a higher risk of hip fracture^[1].

What this means

The study adds RSV to the list of infections that are followed by a period of higher cardiovascular risk, and it puts a number on it: in older Danish adults with a confirmed infection, roughly one additional heart or circulation problem for every 20 people within a year^[1]. The authors conclude that RSV should be seen not only as a respiratory virus but also as a possible risk factor for cardiovascular disease, and that the findings support prevention, especially vaccination, in older adults^[1].

Two findings help to keep this in proportion. First, the excess was concentrated in people who were seriously ill. People who were not admitted to hospital had no measurable extra risk, and patients with a hip fracture or a urinary tract infection had even more cardiovascular events than patients with RSV^[1]. This suggests that serious illness in general, rather than something unique to this virus, may explain a large part of the effect. Second, the comparison with flu fits the earlier evidence that respiratory infections can trigger cardiovascular events^[1,2].

Whether vaccination actually prevents these heart problems is a separate question, and the first trial evidence is mixed. In DAN-RSV, a large Danish trial that randomly assigned 131,276 adults aged 60 and over to an RSV vaccine or no vaccine during the 2024–2025 winter, hospital admissions for heart or lung disease were about 10% less frequent in the vaccinated group (26.3 versus 29.2 per 1,000 person-years). Admissions for cardiovascular disease alone were also slightly lower (16.4 versus 17.7 per 1,000 person-years), but that difference could have been due to chance. The trial was funded by Pfizer^[4].

Several countries already recommend RSV vaccination for older adults, mainly to prevent severe lung disease. In Germany, for example, the national vaccination committee (STIKO) recommends a single dose for everyone aged 75 and over, and for people aged 60 to 74 with severe chronic conditions – including chronic heart and circulation disease – or who live in a care home, ideally in late summer or autumn^[5]. Recommendations differ between countries. Anyone unsure whether they should be vaccinated can discuss it with their doctor.

A note on interests: the paper contains no funding statement; the analysis was carried out as part of the institute's national surveillance work. Two of the four authors report payments from pharmaceutical companies that also produce vaccines, all outside the submitted work^[1].

What the study cannot tell us

• Association, not proof of cause: the groups were matched for age, sex and recorded diseases, but not for lifestyle or social factors. The authors name such unmeasured confounding as a limitation^[1].
• More severe infections were likely overrepresented: only infections confirmed by a laboratory test were counted, and 69% of people with RSV were in hospital. The results therefore mainly describe people ill enough to be tested, not the many people with mild, untested RSV^[1].
• Missed infections in the comparison group: some “uninfected” people may have had RSV without being tested. According to the authors, this would tend to make the measured difference smaller, not larger^[1].
• One country: Denmark has a relatively homogeneous population and a universal health care system. The authors caution that the exact numbers may not transfer to countries with different populations or health systems^[1].
• Hospital diagnoses only: events were taken from hospital diagnosis codes, so milder problems never seen in hospital were not counted^[1].
• No data on vaccination benefit: the study did not test whether RSV vaccination prevents cardiovascular events; the authors call for research on exactly that^[1].