Medical Oncologist
After rituximab treatment
Low Antibodies and Repeated Infections — After Rituximab
Rituximab works by depleting B cells — the cells that make your antibodies. When antibody levels fall and stay low, infections that your body would normally handle quickly can become serious. Knowing when to act changes the outcome.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- Expected but not harmless — Low antibodies after rituximab are a known effect, not a sign something went wrong. But they do raise your infection risk.
- Some infections need emergency care — Fever with shaking chills, difficulty breathing, or confusion are not wait-and-see symptoms.
- Mild infections can be monitored — A runny nose or sore throat without fever can often be watched at home for a day or two with your team's guidance.
- The pattern matters — Repeated infections over a few months are a signal your team needs to know about, not a run of bad luck.
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Rituximab depletes B cells, which can lower your antibody levels for months. Lower antibodies mean your body is slower to fight infections. Most infections are manageable, but fever with shaking chills, difficulty breathing, or confusion always need same-day emergency care. Call your team the same day for any new infection that does not improve within 24 to 48 hours.
Which infections can you manage at home?
A mild cold — runny nose, mild sore throat, no fever — can often be watched at home, with paracetamol for comfort and plenty of fluids.
Mild sinus congestion without fever, and a dry cough without breathlessness, are also usually safe to monitor for a day or two.
But monitoring has a limit. If any symptom worsens, or if fever develops at any point, call your oncology team the same day. Do not wait for your next scheduled appointment.
When should you call your oncology team the same day?
Call the same day if you develop any fever, if an infection has not improved after a day or two of home management, or if you feel worse rather than the same.
Also call if you have had repeated separate infections over a few months — chest, sinuses, urinary, or skin. A recurring pattern is one of the clearest signs that your antibody levels need to be checked.
Your team may arrange a blood test to measure your immunoglobulin levels. That result guides whether further action — such as antibody replacement infusions — is needed.
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How do you tell a manageable infection from one that needs urgent care?
| Feature | Watch at home | Call today | Go to emergency now |
|---|---|---|---|
| Fever | None | Any new fever | High fever with rigors or shaking chills |
| Breathing | Normal | Mild cough, no breathlessness | Any breathlessness or chest pain |
| Alertness | Tired but alert | Noticeably more tired or unwell | Confused, drowsy, or hard to rouse |
| Direction of symptoms | Improving day by day | Not improving after 24–48 hours | Getting worse by the hour |
| Skin | No change | Localised redness, not spreading | Redness spreading rapidly, warm and swollen |
| Typically starts | Any time after rituximab begins | Weeks to months after first dose | Can occur months after last dose |
Questions families commonly ask
What does 'low antibodies' actually mean?
Rituximab targets CD20, a marker on B cells — the cells responsible for making antibodies, also called immunoglobulins. When B cells are depleted, your body produces fewer antibodies over time. Lower antibody levels mean your immune system has less ready-made defence against bacteria in particular. Your team can measure your IgG level with a blood test to see how low it has fallen and whether treatment to replace the antibodies is needed.
Will I need immunoglobulin infusions?
Not everyone with low antibodies after rituximab needs infusions. ESMO and NCCN guidance indicates that replacement is considered when levels fall below a certain threshold and when repeated serious infections occur. Your oncologist makes that decision based on both the blood result and your clinical pattern — how often you are getting infections and how severe they are. If your team has not discussed this and you have had repeated chest or sinus infections, it is a reasonable question to raise at your next appointment.
How long will my antibody levels stay low?
B cells can remain depleted for six months or more after rituximab treatment ends, and immunoglobulin levels may lag behind the B cell recovery. The timeline varies significantly from person to person and depends on how many cycles you received and your individual immune system. Your team will monitor your levels with periodic blood tests. Recovery is possible for many people, though it is not guaranteed to return to the level it was before treatment began.
Can I still be vaccinated?
Vaccines that use live or weakened viruses — such as yellow fever or the nasal flu spray — are generally avoided while your immunity is suppressed. Inactivated vaccines such as the injected influenza vaccine and pneumococcal vaccines may still be given, though your immune response may be weaker than usual. Your oncologist can advise on timing, and keeping close family members up to date with their vaccinations can provide some indirect protection for you.
Should we avoid crowded places or visitors?
You do not need to become completely isolated, and for most people that would not be realistic or sustainable. Reasonable precautions include avoiding people who are visibly unwell, wearing a mask in crowded indoor spaces during peak infection seasons, and practising good hand hygiene. Your oncology team will give specific guidance based on how low your counts are. The goal is proportionate precaution, not complete withdrawal from everyday life.
Did you know?
B cell depletion after rituximab can persist for six months or more, and low immunoglobulin levels can last even longer — sometimes well beyond the end of treatment.
This is why a new infection months after your last dose still needs the same prompt reporting as an infection during active treatment.
Source: ESMO Clinical Practice Guidelines: Haematological Malignancies
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Common questions
Frequently asked questions
Is it normal to keep getting infections after rituximab?
Repeated infections after rituximab are a recognised pattern, not coincidence. Rituximab depletes the B cells that make antibodies, and lower antibody levels mean your body is slower to fight off bacteria in particular. If you have had repeated infections in a few months — chest, sinuses, skin, or urinary — tell your oncologist. Blood tests can measure your immunoglobulin levels and guide whether anything further needs to be done. Reporting the pattern is more useful than managing each infection separately.
My oncologist said my IgG is low. What does that mean for me?
IgG is the main antibody that protects you from bacterial infections. When it falls, your risk of chest and sinus infections in particular goes up. Whether that level needs treatment depends on how low it is and whether you are already having repeated infections. Your oncologist may recommend monitoring or may discuss antibody replacement infusions if the pattern is significant. Ask specifically what your result showed, what the concern threshold is, and what the plan is if you get another infection.
Can I take antibiotics at home when I get an infection?
Not without checking with your oncology team first. Some teams do give patients a prescription to have at home for use at the first sign of a chest infection, as part of a specific agreed plan. But starting antibiotics on your own, without that prior agreement, can mask symptoms your team needs to see. Call your team before taking anything, unless you are already following a written plan they gave you. If you cannot reach them and you have a fever, go to emergency care.
What is the difference between a normal cold and something serious?
A normal cold typically brings a runny nose, mild sore throat, and mild tiredness, with no fever, and improves over a few days. Something that needs urgent attention is when any fever develops, when breathing becomes difficult, when you feel dramatically worse, or when the illness does not follow the usual improving pattern. After rituximab, fever at any level is a same-day call, and breathlessness or confusion is an emergency department visit, not a call.
Should I tell the emergency department about my rituximab treatment?
Yes, and immediately — tell the person who first sees you that you have had rituximab, that your immunity may be reduced, and that you are being treated for cancer. This changes how urgently they assess you and which tests they order. Carry a brief written note if you can — your diagnosis, your treatment name and when you last received it, and your oncologist's contact number. Many oncology departments provide a card for exactly this purpose; ask your team if they can give you one.