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Why FluPulse™ exists

A flu vaccine every year is the right call, and nothing on this page changes that. But a flu vaccine does not protect everyone equally. People whose immune system is weakened, by a transplant, cancer treatment, dialysis or medicines that suppress immunity, respond less strongly to flu vaccines than healthy adults: across more than 200 studies, their odds of reaching a protective antibody level after vaccination were roughly a third to a half of those of healthy people, and the response is weakest after an organ or stem-cell transplant or treatment that removes antibody-producing cells.[2][3][4] The vaccine still helps them, which is why it is still recommended; it helps less. For people whose immune system or lungs, heart or kidneys are already under strain, flu can therefore still mean a hospital stay, even in a year when they were vaccinated. FluPulse was built so that those people, and the people who care for them, know when flu, RSV and COVID are rising where they live, and can act early: masks in crowded rooms, a call to the clinic at the first symptoms, antiviral medicine without delay.

The study behind it

In 2023, a research team at Janssen (part of Johnson & Johnson), which included FluPulse's founder, looked at the insurance records of 5,195,160 adults in the United States who had received a flu vaccine. The records covered four flu seasons, 2015 to 2019, before COVID. For each person the team noted the health conditions they already had, then watched the rest of that flu season for two things: a visit to a doctor or hospital for a flu-like illness, and a hospital stay within 30 days of that visit.

What they found

Across everyone in the study, flu-like illness that needed medical care was fairly common and hospitalization for it was rare: in a year, about 2 of every 100 vaccinated adults saw a doctor for a flu-like illness, and about 1 in 400 were hospitalized for one.

For some groups the picture was very different. Compared with vaccinated adults as a whole, the chance of being hospitalized with a flu-like illness was:

• about 6 to 14 times higher for people living with an organ or stem-cell transplant,
• about 5 to 7 times higher for people with advanced kidney disease,
• about 5 times higher for people with severe long-term lung disease.

In the highest-risk groups, as many as half of the people who caught a flu-like illness ended up in hospital with it. And because conditions like COPD, heart failure and advanced kidney disease are common, more than half of all the flu-related hospital stays in the study were in people with one of those three conditions.

The researchers concluded that people with a weakened immune system, or with severe long-term heart, lung or kidney disease, carry the highest remaining risk of a flu hospitalization even after vaccination, and that extra protection on top of the vaccine could help them.[1]

Other studies point the same way. In Auckland, New Zealand, adults with heart failure, advanced kidney disease or COPD were hospitalized with laboratory-confirmed flu at roughly 3 to 13 times the rate of adults without those conditions.[5] In two US health systems over the 2016 to 2020 seasons, heart failure carried about four times the rate of flu hospitalization, and the rate rose with each additional condition, after accounting for vaccination.[6] Among 35,000 adults hospitalized with confirmed flu across the United States, those with a weakened immune system were more likely to die and stayed in hospital longer, even though more of them had been vaccinated.[7] And in a typical season about 95 of every 100 adults hospitalized with flu have at least one chronic condition.[8] Those studies counted everyone, vaccinated or not; the Janssen study is one of the few to look only at people who had been vaccinated.

What the study does not say

It does not say the vaccine failed. Everyone in the study was vaccinated, so it cannot measure how much the vaccine helped; other studies do that, and the vaccine is still recommended for every one of these groups. It counts "flu-like illness" from the diagnosis a doctor recorded, not from a laboratory test, so some of those illnesses were other viruses. It counts only people who sought care, from one set of US insurance plans. And it shows which conditions go with higher risk, not what each person's own risk is. If you have one of these conditions, the right place to take that question is your own doctor.

What it means for you

If you or someone you care for has a transplant, advanced kidney disease, heart failure, COPD or another serious long-term condition, timing matters more for you than for most people. Knowing that flu is rising in your county before it peaks gives you time to use the protection you already have: get the vaccine if you have not, keep antiviral medicine within reach, and call your doctor at the first symptoms rather than waiting. That is what FluPulse is for.

References

1. Zemlianskaia N, Zheutlin A, Murata Y, Bhattacharya J, Coteur G, Ispas G, Villacian J, Chien J, Hong D, Xu J, Neri B, Sarsour K, Kamath T, Liu X. 2659. Substantially elevated influenza risk in vaccinated immunocompromised adults and high-risk patients relative to all vaccinated. Open Forum Infect Dis. 2023;10(Suppl 2):ofad500.2270. Presented at IDWeek 2023. doi:10.1093/ofid/ofad500.2270 · free full text · poster as presented (PDF, 0.4 MB)
2. Beck CR, McKenzie BC, Hashim AB, et al. Influenza vaccination for immunocompromised patients: systematic review and meta-analysis by etiology. J Infect Dis. 2012;206(8):1250-1259. doi:10.1093/infdis/jis487
3. Kunisaki KM, Janoff EN. Influenza in immunosuppressed populations: a review of infection frequency, morbidity, mortality, and vaccine responses. Lancet Infect Dis. 2009;9(8):493-504. doi:10.1016/S1473-3099(09)70175-6
4. See KC. Vaccination for the prevention of infection among immunocompromised patients: a concise review of recent systematic reviews. Vaccines (Basel). 2022;10(5):800. doi:10.3390/vaccines10050800
5. Walker TA, Waite B, Thompson MG, et al. Risk of severe influenza among adults with chronic medical conditions. J Infect Dis. 2020;221(2):183-190. doi:10.1093/infdis/jiz570
6. Frutos AM, Tenforde MW, Sundaresan D, et al. Influenza-associated hospitalization rates by underlying conditions, 2016-2017 to 2019-2020: a retrospective cohort study. J Infect Dis. 2025;232(4):e642-e650. doi:10.1093/infdis/jiaf164
7. Collins JP, Campbell AP, Openo K, et al. Outcomes of immunocompromised adults hospitalized with laboratory-confirmed influenza in the United States, 2011-2015. Clin Infect Dis. 2020;70(10):2121-2130. doi:10.1093/cid/ciz638
8. Centers for Disease Control and Prevention. People with chronic medical conditions continue to account for the majority of flu hospitalizations this season. January 26, 2024. cdc.gov