Vaccines and Cancer Immunotherapy: How Common Vaccines May Help Your Treatment Work Better

Cancer immunotherapy drugs—called immune checkpoint inhibitors (ICIs)—help your immune system recognize and attack cancer cells. ICIs such as pembrolizumab (Keytruda) and nivolumab (Opdivo) block the so-called PD-1 checkpoint that normally keep the immune system from overreacting. By releasing these brakes, the immune system can stay active against cancer longer. Recent research shows that common vaccines, such as the flu shot and COVID-19 mRNA vaccines, may make these treatments work even better—not just protect you from infections.

1. The Flu Shot and Survival During Immunotherapy

A large European study (Bersanelli M et al, eClinicalMedicine 2023;61: 102044) called INVIDIa-2 followed over 1,000 patients with advanced cancers receiving ICIs. Half received the seasonal flu vaccine, and half did not. Results showed vaccinated patients lived longer: overall survival (27 vs 21 months), longer cancer control (PFS +3 months), and higher disease control rate (75% vs 67%). Even though vaccinated patients were generally older and sicker, they still lived longer—suggesting the vaccine itself may boost immune response.

What those terms mean:
• Overall survival (OS): How long patients lived after starting treatment.
• Progression-free survival (PFS): How long before the cancer grew or spread again.
• Disease control rate (DCR): The percentage of patients whose cancer shrank or stayed stable.

Timing of the Flu Shot

Doctors initially wondered whether getting the flu shot too early—right when immunotherapy begins—might distract the immune system. However, in the INVIDIa-2 study, no negative timing effect was seen. Patients who received the vaccine during or after starting treatment actually lived longer. This suggests the flu shot is safe and likely beneficial at any point during immunotherapy.

2. COVID-19 mRNA Vaccines and Better Outcomes

A recent study (Grippin et al, Nature 2025; 647, 488–497) analyzed more than 1,300 patients with lung cancer and melanoma receiving ICIs. Those who received an mRNA COVID-19 vaccine (Pfizer or Moderna) within about 100 days before or after starting treatment lived significantly longer— 37 vs 21 months in lung cancer and a 63% survival improvement in melanoma. The effect was specific to mRNA vaccines. Laboratory studies showed mRNA vaccines stimulate strong type-I interferon and T-cell responses, supporting ICI activity.

3. How Vaccines and Immunotherapy Work Together

Vaccines act as an alarm that briefly stimulates the immune system, while ICIs remove the brakes that normally calm it down. Together, they can keep the immune system on alert longer and help it better recognize cancer cells—think of it as the vaccine pressing the accelerator and immunotherapy keeping your foot on the gas.

4. Safety and Timing

Large studies show vaccines are safe during immunotherapy and do not increase immune-related side effects. The best timing appears to be within a few weeks before or after starting treatment, especially for mRNA COVID-19 vaccines. Avoid live vaccines (nasal flu spray or older shingles vaccine) unless your oncologist approves.

5. What You Can Do

6. The Bottom Line

Vaccines like the flu shot and COVID-19 mRNA boosters are safe, protective, and may even help immunotherapy work better. They’re a simple, low-risk step to give your immune system an extra edge in fighting cancer.