Can I Have the COVID Vaccine if I Am Having Chemotherapy?

People receiving chemotherapy can and should get COVID-19 vaccines. Every major oncology society, including the American Society of Clinical Oncology, recommends vaccination for patients on active cancer treatment, and multiple studies confirm that the vaccines are safe in this population. The picture does get more complicated when you look at how well the vaccines work during chemotherapy, because the immune response is measurably weaker than in healthy adults. But weaker protection is not zero protection, and the risk of severe COVID-19 for someone on chemotherapy far outweighs the risk of vaccination.

Side Effects Are Similar to What Everyone Else Gets

One of the most common worries is that a vaccine might cause unusually severe reactions in someone whose immune system is already under pressure from chemotherapy. The evidence says otherwise. In a study of 210 patients with solid tumors on systemic therapy, only about 18% experienced a side effect attributed to the vaccine, and the vast majority of those were mild: fatigue, fever, injection-site soreness, and chills. Only nine events were graded as moderate, and no severe vaccine-related events occurred.

Larger trials tell a consistent story. The VOICE trial, which enrolled patients on chemotherapy, immunotherapy, and combination regimens, found that serious adverse events (grade 3 or worse) occurred in roughly 1–2% of patients across treatment groups, with only four events considered potentially vaccine-related. There were no vaccine-related deaths.² A separate Israeli study of over 300 actively treated cancer patients found no severe, life-threatening, or hospitalization-requiring side effects at all.³

The practical concern for many patients is whether a vaccine reaction might delay their next chemotherapy session. In the study of 210 patients, treatment was postponed by two weeks in only three people, about 1.4% of the group.¹ Another prospective study found zero vaccine-related interruptions to cancer therapy.⁴ The short version: getting vaccinated is very unlikely to throw your treatment schedule off track.

The Vaccine Works, but Not as Well as in Healthy People

Safety is only half the question. What people really want to know is whether the vaccine will actually protect them if their immune system is being suppressed. The honest answer is that chemotherapy blunts the antibody response, sometimes substantially, but most patients still develop measurable immunity.

After two doses, cancer patients on chemotherapy produced antibody levels that were roughly half to one-eleventh of what healthy adults generated, depending on the study and the specific measurement used.⁵⁶ One study comparing patients on chemotherapy to those on non-chemotherapy treatments found the chemotherapy group had an antibody titer nearly ten times lower.⁷ That’s a big gap, but it doesn’t mean the vaccine is useless. In the same Nature Medicine study, 80% of cancer patients developed detectable virus-neutralizing antibodies after two doses. Not perfect, but far better than nothing.

The VOICE trial added more texture. Patients on chemotherapy alone reached near-universal antibody positivity at about 97%, while those on immunotherapy or combination regimens hit 99–100%.² So for people with solid tumors on standard chemotherapy, the vaccine reliably produces some antibody response even if the levels are lower.

Blood Cancers Are a Different Story

The type of cancer matters enormously. Patients with solid tumors like breast, lung, and colorectal cancers tend to respond reasonably well to vaccination, with seroconversion rates at or above 90%. Patients with blood cancers — leukemias, lymphomas, myeloma — often fare much worse. In one study, only about 50% of patients with blood cancers developed antibodies above the positivity threshold, compared to over 90% for solid tumors.⁵ Patients with non-Hodgkin lymphoma fared worst of all.

A direct comparison study confirmed that patients with blood cancers had significantly lower neutralizing antibody levels than those with solid cancers, regardless of which vaccine they received.⁸ This gap widened further with newer Omicron subvariants: patients with blood cancers showed neutralizing antibody scores roughly a third of those seen in solid tumor patients for the BA.1, BA.2, and BA.4/5 subvariants.⁹

B-cell depleting therapies such as rituximab are the biggest culprits here. These drugs wipe out the very immune cells responsible for producing antibodies. Research suggests that waiting at least nine months after rituximab before vaccinating gives the best chance for naïve B cells to repopulate and mount a response.¹⁰ That said, even when B-cell depleting therapies blunt the antibody response, whether this actually translates into higher rates of hospitalization or death remains unclear.¹¹ One reason for that uncertainty is T cells.

T Cells Pick Up Some of the Slack

Antibody levels get the most attention, but the immune system has another line of defense that matters here. T cells, which recognize and kill infected cells directly, appear to respond to vaccination even in patients whose antibody responses are poor. A study examining patients on chemotherapy, immunotherapy, and B-cell directed therapies found that T-cell responses to the spike protein were similar across all groups, including healthy controls.¹²

Even among patients who were seronegative — meaning they had no detectable antibodies — 11 out of 13 tested still developed T-cell responses to the spike protein. That included six of eight patients on B-cell depleting therapies, the very group expected to have the weakest immunity. Cross-reactive T cells recognizing the Delta variant were detected in roughly half the patients tested.¹² T-cell immunity is harder to measure in clinical practice and doesn’t get reported on routine bloodwork, but it provides a real safety net that antibody levels alone don’t capture.

Timing the Vaccine Around Your Chemotherapy Cycle

If you have the flexibility, when you get vaccinated relative to your chemotherapy schedule can make a difference. The general guidance is to give the vaccine before starting chemotherapy if possible, or between cycles and away from the nadir — the point where your blood counts are at their lowest, typically a week or two after an infusion.¹³ Getting vaccinated when white blood cell counts are recovering gives the immune system more to work with.

That said, one study found that antibody titers after vaccination were lower in the chemotherapy group regardless of when during the cycle the vaccine was given.¹⁴ So timing helps, but it doesn’t fully close the gap. The key takeaway is that you should not delay vaccination waiting for the “perfect” window. Getting the vaccine at a slightly suboptimal time is better than not getting it at all, especially since COVID-19 poses a much higher risk to patients on active treatment.

Watch Out for Corticosteroid Premedication

Many chemotherapy regimens include corticosteroids like dexamethasone as a premedication to prevent nausea and allergic reactions. These steroids are immunosuppressive by design, and they appear to blunt the vaccine response on top of whatever chemotherapy is already doing. Patients who received dexamethasone alongside their chemotherapy had significantly lower antibody titers after vaccination — roughly a third of the level seen in patients not receiving dexamethasone.¹⁵ The effect was dose-dependent: patients on the highest cumulative dexamethasone doses had the lowest antibody titers, and getting the vaccine on the same day as a dexamethasone dose produced the weakest response.

A separate prospective study confirmed that immunosuppressive corticosteroid dosing was independently linked to lower antibody levels after vaccination.¹⁶ This is worth discussing with your oncology team. It may not always be possible to avoid steroids, but spacing the vaccine away from steroid-heavy days could help.

Boosters Make a Real Difference

If the initial vaccine series produces a weaker response in cancer patients, the obvious question is whether additional doses can close the gap. The answer is a clear yes. Booster doses increase antibody levels in patients with solid tumors substantially, and the benefit appears particularly high in patients who had no detectable antibodies after the first two doses.¹⁷ Booster vaccination also improved the ability to neutralize variants of concern.

In terms of hard outcomes, a large U.S. study found that a monovalent booster reduced COVID-19 hospitalizations by about 29% and ICU admissions by about 36% in patients receiving chemotherapy or immunotherapy, compared to those who received only the primary series.¹⁸ Bivalent boosters showed a similar benefit, reducing hospitalizations by about 30%.¹⁸ Those reductions may sound modest compared to what vaccines achieve in healthy populations, but for a group already at elevated risk, preventing roughly one in three severe hospitalizations is meaningful.

For patients with blood cancers, the picture is more mixed. Boosters do help, but the response remains weakest in people on B-cell depleting therapies. Bivalent boosters enhanced neutralizing capacity against certain Omicron subvariants like BQ.1.1, converting about 55% of patients who previously lacked a protective response. However, against more immune-evasive strains like XBB.1 and XBB.1.5, the bivalent boost largely failed to produce adequate neutralizing titers in cancer patients.¹⁹ This is partly why updated vaccine formulations are important: as the virus evolves, keeping booster doses current helps close whatever gap the immune system can manage.

Children With Cancer Face Similar Tradeoffs

Pediatric oncology patients were studied separately, and the patterns mirror what we see in adults, albeit with even less data. After two vaccine doses, about two-thirds of children with cancer developed neutralizing antibodies, and that rose to 80% after a third dose. T-cell responses followed a similar trajectory, with 59% responding after two doses and 74% after three.²⁰ Side effects were generally mild and transient, and the vaccines did not delay cancer treatment.

Children actively receiving therapy had dramatically lower antibody levels than those who had finished treatment — roughly 65-fold lower in one study.²¹ In that study, only a third of children on active therapy reached protective neutralizing levels against the Delta variant, compared to 100% of those off therapy. Additional doses were needed for most children still on treatment. These findings reinforce that children with cancer should be vaccinated, but families should discuss the number and timing of doses with their oncologist.

Swollen Lymph Nodes on Scans After Vaccination

COVID-19 vaccines can cause temporary swelling in the lymph nodes near the injection site, and this is something cancer patients need to know about before getting imaging. On PET/CT scans, vaccine-related lymph node activity can look alarmingly similar to cancer spread. In one review of over 700 PET/CT scans, 85% of recently vaccinated patients showed increased activity in the armpit or deltoid area on the same side as the injection, with a median of 11 days between the shot and the scan.²²

Radiologists have learned to distinguish between the two: vaccine-related lymph node activity tends to show much lower uptake values compared to actual metastatic disease. But in the early days of the vaccine rollout, this caused real diagnostic confusion. Multiple case reports documented patients whose imaging raised concerns about cancer spread, leading to unnecessary biopsies that ultimately showed reactive lymph nodes from vaccination.²³ In breast cancer patients specifically, reactive-only lymph nodes on sentinel node biopsy were 16 percentage points more common in those vaccinated in the prior three months.²⁴

The practical advice: tell your imaging team about your recent vaccination, including which arm and when. If possible, schedule the vaccine in the arm opposite to your cancer or planned imaging. And if you can space the vaccination and a scan apart by a few weeks, that helps avoid ambiguity.

Why Some Patients Still Hesitate

Despite strong guidance from oncology organizations, vaccine hesitancy among cancer patients has been surprisingly high. A rapid review of studies found hesitancy rates ranging from about 4% to 77%, with an average around 38%.²⁵ That enormous spread likely reflects differences in timing, geography, and how the question was framed, but even the most conservative estimate from a large international study put hesitancy at 19%.

The biggest drivers of refusal weren’t general anti-vaccine sentiment. Patients who believed the vaccine might interfere with their treatment or worsen their cancer outcome were roughly six to seven times more likely to refuse vaccination.²⁶ Safety concerns and distrust in authorities also played significant roles. The same research found that oncologist advice was highly valued by patients, which suggests that a clear, direct conversation with one’s cancer doctor is one of the most effective tools for addressing hesitancy. The evidence accumulated since the vaccines became available should make that conversation easier: the vaccines do not interfere with chemotherapy, they do not worsen cancer outcomes, and the side effects in cancer patients are overwhelmingly mild.

Hybrid Immunity and Ongoing Protection

A question that has become increasingly relevant as COVID-19 becomes endemic is what happens when a vaccinated cancer patient also gets infected. The combination of vaccination plus infection — sometimes called hybrid immunity — appears to produce a more robust and durable immune response than either alone. A study in patients with chronic lymphocytic leukemia, one of the more immunocompromised groups, found that those who had a COVID-19 infection followed by three vaccine doses developed strong immune responses across multiple compartments: blood antibodies, mucosal antibodies in saliva, and T cells.²⁷

This is encouraging for the long term. Many cancer patients will encounter the virus at some point regardless of precautions. Having a foundation of vaccine-induced immunity, even if imperfect, likely softens the blow of that encounter and helps build a more comprehensive immune memory afterward. This is also why ASCO’s guidelines emphasize that vaccination plans for cancer patients may need to differ from those for the general population — additional doses, different spacing, and ongoing updated boosters may all be appropriate depending on the type of treatment and the patient’s immune status.²⁸ The conversation about COVID vaccination isn’t a one-time event; it’s an ongoing part of your cancer care.

1
PubMed Central. Short term safety of coronavirus disease 2019 vaccines in patients with solid tumors receiving systemic therapy
2
The Lancet Oncology. Safety and immunogenicity of mRNA-1273 SARS-CoV-2 vaccine in patients with solid tumours receiving chemotherapy, immunotherapy, or chemoimmunotherapy (VOICE trial)
3
JNCI: Journal of the National Cancer Institute. Immunogenicity and Safety of the BNT162b2 mRNA COVID-19 Vaccine Among Actively Treated Cancer Patients
4
medRxiv. Vaccine beliefs, adverse effects, and quality of life in patients with cancer undergoing routine COVID-19 vaccination
5
PubMed Central. Antibody Response to COVID-19 mRNA Vaccines in Oncologic and Hematologic Patients Undergoing Chemotherapy
6
Nature Medicine. Immune responses to two and three doses of the BNT162b2 mRNA vaccine in adults with solid tumors
7
PubMed Central. Difference in Immunogenic Responses to COVID-19 Vaccines in Patients With Cancer Receiving Chemotherapy Versus Nonchemotherapy Treatment
8
PubMed. Comparison of antibody response to coronavirus disease 2019 vaccination between patients with solid or hematologic cancer patients undergoing chemotherapy
9
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10
PubMed Central. Optimal time for COVID-19 vaccination in rituximab-treated dermatologic patients
11
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12
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13
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14
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15
PubMed. Effect of Corticosteroid on Immunogenicity of SARS-CoV-2 Vaccines in Patients With Solid Cancer
16
PubMed Central. Antineoplastic treatment class modulates COVID-19 mRNA-BNT162b2 vaccine immunogenicity in cancer patients
17
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PubMed Central. COVID-19 Vaccine Booster Uptake and Effectiveness Among US Adults With Cancer
19
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20
PubMed. Immune Response to COVID-19 Vaccination in Children With Cancer
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PubMed Central. Immune Response after 2 Doses of BNT162b2 mRNA COVID-19 Vaccinations in Children and Adolescents with Cancer and Hematologic Diseases
22
PubMed Central. COVID-19 vaccine related hypermetabolic lymph nodes on PET/CT: Implications of inflammatory findings in cancer imaging
23
PubMed Central. Lymphadenopathy in COVID-19 Vaccine Recipients: Diagnostic Dilemma in Oncologic Patients
24
PubMed Central. Axillary Lymph Nodes in Breast Cancer Patients After COVID-19 Vaccine
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PubMed Central. Vaccination of Adults With Cancer: ASCO Guideline