Kesimpta (ofatumumab) starts depleting B cells within days, reaching its target level in about 11 days after the first injection. But the timeline for noticing real-world benefits, like fewer relapses or stable MRI scans, stretches over weeks to months depending on what you’re measuring. Here’s what to expect at each stage.
What Happens in the First Two Weeks
Kesimpta works by targeting and destroying a specific type of immune cell called B cells, which play a central role in the nerve damage of relapsing multiple sclerosis. The drug gets to work fast. After the first subcutaneous injection, it reaches peak concentration in the blood in about 4.3 days. By day 11, median B-cell counts drop below the therapeutic target of 8 cells per microliter. That’s a dramatic reduction from the normal range of roughly 100 to 500 cells per microliter.
The initial dosing schedule is designed to accelerate this process. You receive three loading doses: one injection each at week 0, week 1, and week 2. After that, you switch to one injection per month starting at week 4. Those closely spaced loading doses help drive B cells down quickly and keep them suppressed, with counts converging to a median of about 1.4 cells per microliter over time. Between monthly doses, there’s negligible rebound in B-cell numbers.
When Relapses Start to Decrease
B-cell depletion within the first two weeks is a biological event happening beneath the surface. The clinical payoff, fewer MS relapses, takes longer to become apparent. In the large ASCLEPIOS clinical trials, patients on Kesimpta had an annualized relapse rate of 0.128 during the first year. To put that in perspective, that’s roughly one relapse every eight years on average.
The relapse rate continued to drop with longer treatment. By year five, it fell to 0.034, meaning relapses became exceedingly rare. While the trials didn’t pinpoint the exact week relapses began declining, the rapid B-cell depletion within the first two weeks strongly suggests protective effects begin building almost immediately, even if you won’t notice them as a single clear moment of improvement.
When MRI Scans Show a Difference
MRI scans are one of the most sensitive ways to detect whether a treatment is controlling MS activity, often catching disease changes before you’d ever feel symptoms. On Kesimpta, the suppression of new brain lesions was profound from the first year of treatment onward. During year one, patients averaged just 0.025 gadolinium-enhancing lesions per scan, which is essentially close to zero. By year five, that number dropped even further to 0.009.
New or enlarging lesions on a different type of MRI sequence followed a similar pattern. The average count fell from about 1.2 in year one to 0.06 by year five. Your neurologist will likely schedule an MRI a few months into treatment to establish a new baseline and check for ongoing disease activity. Most people see dramatically cleaner scans within the first six to twelve months.
How Long Before Disability Stabilizes
Preventing disability progression is the most meaningful long-term goal of any MS therapy, and it’s also the slowest outcome to measure. In clinical trials, disability was tracked using a standardized neurological exam that scores physical function on a scale. A meaningful worsening had to be sustained for at least three or six months before it counted as true progression, which filters out temporary flare-ups.
Over five years of treatment, more than 80% of patients on Kesimpta remained free of six-month confirmed disability worsening. Brain volume loss, another marker of long-term damage, stayed low at roughly 0.3% per year, which is close to the rate seen in healthy aging. Blood levels of neurofilament light chain, a protein released when nerve fibers are damaged, also remained low through five years of follow-up. These numbers suggest that while you won’t feel disability stabilization as a distinct event, the protective effect accumulates steadily from the early weeks of treatment.
When You Might Feel Different Day to Day
Fatigue is one of the most common and frustrating symptoms of MS, and many people starting Kesimpta want to know if they’ll actually feel better, not just see better lab results. The honest answer is that subjective improvement is slower and less dramatic than the biological changes happening underneath.
A meta-analysis of studies on high-efficacy MS treatments (the class Kesimpta belongs to) found a small but statistically significant improvement in fatigue scores after 6 to 12 months of treatment. That improvement roughly doubled when measured at 18 to 24 months. Physical fatigue specifically showed the most measurable reduction. So if you’re hoping to feel less wiped out, give it at least six months before drawing conclusions, and expect gradual improvement rather than a sudden shift.
The Full Timeline at a Glance
- Days 1 to 11: B cells drop below the therapeutic target. The immune mechanism driving your MS is already being disrupted.
- Weeks 2 to 4: B-cell depletion is sustained through loading doses. Biological protection is building, though you likely won’t notice changes yet.
- Months 3 to 6: Your neurologist may order follow-up MRIs. Most patients show significant suppression of new lesion activity by this point.
- Months 6 to 12: Relapse rates are measurably low. Some patients begin noticing improvements in fatigue and daily functioning.
- Years 2 to 5: Efficacy continues to improve. By year two, 80% of patients in trials showed no evidence of disease activity (no relapses, no new lesions, no disability worsening). By year five, that figure reached 93%.
Why the “Working” Timeline Feels Unclear
The challenge with MS treatments is that success often looks like nothing happening. If you’re not relapsing, not developing new lesions, and not getting worse on neurological exams, the drug is doing its job. That’s a fundamentally different experience from, say, taking a painkiller and feeling relief within an hour. Kesimpta starts reshaping your immune system within the first two weeks, but the full clinical picture takes months to a year to come into focus. The strongest evidence that it’s working comes from your MRI results and relapse history over time, not from how you feel on any given day.