The following article features coverage from the European Society for Medical Oncology (ESMO) Congress 2021. Click here to read more of Cancer Therapy Advisor’s conference coverage.

The relative risk of developing COVID-19 was more than 20 times higher for unvaccinated  patients with cancer than for vaccinated patients with cancer, according to findings from a real-world study presented at the European Society for Medical Oncology (ESMO) Congress 2021.    

Most vaccinated patients had no or mild side effects, and the majority of patients on active cancer treatment were able to continue their treatment as normal. 

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The study included 1069 patients who used, a digital health application for patients with cancer. The patients replied to a targeted survey in April 2021, before the delta variant of SARS-CoV-2 had become widespread.

A majority of patients were women (79.5%), 50 to 69 years of age (72%), and based in North America (91%).

The most common diagnoses were breast (35.2%), gynecologic (14.4%), gastrointestinal (13.3%), lung (9.7%), and genitourinary (7%) cancers. In the 12 months prior to COVID-19 vaccination, patients had received chemotherapy (59%), immunotherapy (14.2%), and radiotherapy (32.8%).

Most patients were vaccinated against COVID-19, though 9.5% were not. Of the unvaccinated group, 4.9% said they did not want to be vaccinated, and the remainder said they weren’t vaccinated yet.

Vaccine types included Pfizer-BioNTech (46.2%), Moderna (36%), Johnson & Johnson (4.1%), and Oxford-AstraZeneca (4.1%).

Ultimately, 0.4% of vaccinated patients developed COVID-19 compared with 8.9% of unvaccinated patients.

The relative risk of developing COVID-19 was 21.5 times higher among unvaccinated patients than among vaccinated patients (95% CI, 6.76-68.77; P <.0001).

Among the vaccinated patients, most reported no side effects (39.3%) or mild ones (43%). However, 2.4% of patients reported severe side effects.     

Side effects typically lasted 1 to 3 days (89.4%). The most common were sore arm (42.5%), headache (23.3%), fatigue (21.1%), and increased temperature (18.5%). Less common were swollen lymph nodes (0.7%) and allergic reactions (0.7%).

Roughly half of patients were vaccinated while on active cancer treatment (49%). For most of these patients (96%), vaccination did not affect their treatment schedule. However, 2.1% of patients had their treatment delayed up to a week, 1.3% had it delayed longer than a week, and 0.6% had it stopped altogether.    

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.

Read more of Cancer Therapy Advisor’s coverage of ESMO 2021 by visiting the conference page.


Sapir E, Moisa N, Litvin A et al. SARS-CoV-2 vaccines in cancer patients (pts), real-world data (RWD) from 1069 users. Presented at: European Society for Medical Oncology (ESMO) Congress 2021; September 16-21, 2021. Abstract 1594P.