Bitten Again: Rabies PEP in a Previously-Vaccinated Patient on Rituximab
A single patient, bitten by a bat in her attic, with a rabies vaccination history from years before her current B-cell-depleting therapy. The disagreement is whether her prior vaccine record still means what it would in someone whose immune system hasn't since been deliberately suppressed.
N.P., a 47-year-old wildlife rehabilitation volunteer, received the full pre-exposure rabies vaccination series nine years ago, back when her work regularly put her in contact with injured bats and raccoons brought in by concerned neighbors. She stopped active fieldwork four years ago after being diagnosed with rheumatoid arthritis and started on rituximab eighteen months ago for disease that hadn't responded adequately to earlier therapies. Two days ago, clearing out her elderly mother's attic, a bat she disturbed bit her on the forearm before flying off; the bat wasn't captured for testing. She came to the emergency department promptly, wound cleaned and irrigated, and her vaccination history from nine years ago is documented clearly in her old employee health records. Her most recent rituximab infusion was four weeks ago — near the trough of B-cell depletion rather than partway through a between-dose recovery, which is the worst point in her treatment cycle at which to need a memory response.
Standard ACIP guidance for a previously-vaccinated person is simple and well-established: two booster doses of rabies vaccine, days 0 and 3, no HRIG needed, regardless of how long ago the original series was completed or whether a titer is checked — because the entire premise of that abbreviated regimen is that prior vaccination reliably primes a fast anamnestic antibody response on re-exposure to antigen. That premise depends on functioning B-cell memory. Rituximab depletes CD20-positive B cells specifically, and while memory plasma cells that already secrete antibody are relatively spared, the rapid recall expansion an anamnestic response requires draws on the memory B-cell pool rituximab is designed to eliminate — which is exactly the mechanism the standard abbreviated regimen assumes will fire reliably. Whether it still will in her case, eighteen months into B-cell-depleting therapy, is not a question the standard guidance was written to answer. And the abbreviated regimen's real hazard is not that it might underperform. It is that it looks identical whether it works or not — no titer is drawn, no response is confirmed — so the first evidence that the anamnestic response failed would be rabies.
Emergency department, hour four
I'd follow the standard abbreviated regimen — two booster doses, days 0 and 3, no HRIG. ACIP's guidance for a documented previously-vaccinated person doesn't carve out an exception for immunosuppression, and given how well-validated this protocol is, I'm cautious about improvising a modification without rabies-specific data behind it.
If her vaccination history were undocumented or uncertain, I'd already be recommending the full series — it's specifically the clarity of her prior vaccination record that makes me want to follow the standard abbreviated protocol here.
I'd treat her as functionally unvaccinated — full primary series plus HRIG. Rituximab depletes the memory B-cell pool the abbreviated regimen's entire rationale depends on for a fast anamnestic response. Her CD19-positive count is under 1% right now. Given rabies is essentially uniformly fatal once symptomatic, the cost of over-treating a possibly-intact response is nothing next to under-treating a genuinely blunted one.
I understand the instinct to follow established protocol precisely — but that protocol was written assuming a functioning memory B-cell compartment, which her labs suggest she may not currently have. Following it exactly here isn't caution, it's applying a rule outside the population it was validated in.
I'd start the abbreviated regimen today — it can't wait for a titer, and adding it does no harm even if we end up doing more — while sending an RVNA titer in parallel. If it comes back low or her B cells show no sign of reconstitution, we add HRIG and additional vaccine doses; if it's robust, we've avoided over-treating on a mechanism concern alone.
This isn't a compromise for its own sake — it's using data that's actually available, just not immediately, rather than committing fully to either extreme before we have to.
Agreed: abbreviated vaccine regimen started today, RVNA titer and B-cell subset panel sent in parallel, with an explicit plan to add HRIG and complete a full primary series if the titer returns low or her B cells show no evidence of reconstitution.
Not resolved as a general policy: the infectious disease physician's preference for following ACIP guidance without modification remains a reasonable default position for most previously-vaccinated patients, and the group was explicit that today's staged approach reflects her specific, documented B-cell depletion rather than a standing exception for every immunosuppressed patient regardless of which drug or how recently dosed.