# Real-World Assessment of Recommended COVID-19 Vaccination Waiting Period after Chemotherapy

## TL;DR

This study found that waiting at least three months after chemotherapy before getting a COVID-19 vaccine reduces infection and hospitalization risks in cancer patients.

## Contribution

The study provides real-world evidence supporting the recommended three-month waiting period for vaccination after chemotherapy.

## Key findings

- Vaccination within three months of chemotherapy increased the risk of COVID-19, UTIs, and sepsis.
- Waiting three months reduced hospitalization risks for cancer patients.
- The findings support current vaccination timing guidelines for cancer patients.

## Abstract

There is a knowledge gap concerning the proper timing for COVID-19 vaccination in cancer patients undergoing chemotherapy. We aimed to evaluate the suitability of the guidelines that recommend waiting at least three months after undergoing chemotherapy before receiving a COVID-19 vaccine. This retrospective cohort study used aggregated data from the TriNetX US Collaboratory network. Participants were grouped into two groups based on the interval between chemotherapy and vaccination. The primary outcome assessed was infection risks, including COVID-19; skin, intra-abdominal, and urinary tract infections; pneumonia; and sepsis. Secondary measures included healthcare utilization and all causes of mortality. Kaplan–Meier analysis and the Cox proportional hazard model were used to calculate the cumulative incidence and hazard ratio (HR) and 95% confidence intervals for the outcomes. The proportional hazard assumption was tested with the generalized Schoenfeld approach. Four subgroup analyses (cancer type, vaccine brand, sex, age) were conducted. Sensitivity analyses were performed to account for competing risks and explore three distinct time intervals. Patients receiving a vaccine within three months after chemotherapy had a higher risk of COVID-19 infection (HR: 1.428, 95% CI: 1.035–1.970), urinary tract infection (HR: 1.477, 95% CI: 1.083–2.014), and sepsis (HR: 1.854, 95% CI: 1.091–3.152) compared to those who adhered to the recommendations. Hospital inpatient service utilization risk was also significantly elevated for the within three months group (HR: 1.692, 95% CI: 1.354–2.115). Adhering to a three-month post-chemotherapy waiting period reduces infection and healthcare utilization risks for cancer patients receiving a COVID-19 vaccine.