Why Dr Shankar: Dr Abhishek Shankar is an associate professor of radiation oncology at the All India Institute of Medical Sciences, Patna. He has been working on preventive oncology for years and trains primary healthcare physicians in detecting early stages of cancer. An editor for several cancer journals, he has previously worked at AIIMS, Delhi and Lady Hardinge Medical College.
Vaccine effectiveness is lower and drops faster in cancer patients compared to healthy individuals. A study by the Lancet Oncology journal found that a Covid-19 vaccine was 69.8 per cent effective in preventing a breakthrough infection in healthy individuals as compared to 65.5 per cent in cancer patients. The vaccine’s effectiveness, measured three to six months after the second dose, dropped sharply for cancer patients and stood at 47 per cent compared to 61.4 per cent in healthy individuals. The effectiveness was found to be the lowest in those undergoing systemic anti-cancer treatments such as radiotherapy. The effectiveness was also found to be lower in those who had leukaemia (blood cancer) or lymphoma (cancer of lymph system cells) compared to those with solid organ cancers. The study included data from 3.7 lakh cancer patients and 2.8 crore healthy individuals.
A recent Lancet study shows Covid vaccines are less effective in cancer patients. What does this mean?
I think the conclusions of the study are a little flawed; let me tell you why. How do we measure vaccine effectiveness? We see how many people in a particular group develop a breakthrough infection after complete vaccination. Now, tell me who is more likely to get the infection – a healthy person who stays at home when there is a surge in the number of Covid-19 cases or a person who continues to visit a hospital regularly for treatment despite the numbers? Those going to hospitals are more likely to be exposed to the virus and hence more likely to develop the infection.
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This is also the reason why the study found the effectiveness of the vaccine to be the lowest among those undergoing treatments such as chemotherapy. Patients under chemotherapy have to visit their hospital regularly and are exposed to the virus. Similarly, leukaemia patients have to be admitted to the hospital for about 14 days initially, but those with solid cancers do not.
They have also looked at vaccine effectiveness in patients in different stages of cancer. Now a patient with stage 4 cancer has to keep going to the hospital for tests and chemotherapy fairly regularly. These patients are exposed to that environment again and again and that is a major predictor of an infection. They have a great dataset – and, it is almost impossible to get such granular, electronic patient data in India even from premier institutes like AIIMS – but I would have liked to know which vaccine works better in which sub-group of cancer patients.
But isn’t the immune response poorer in cancer patients compared to healthy individuals?
Yes. We usually see lower antibody titres in cancer patients, especially those who are undergoing chemotherapy or radiotherapy as these treatments suppress their immune system. In such a condition, when the cells that fight off an infection are not working properly, the antibody levels developed by these cells against the vaccine, or even a natural infection, are lower. Anyway, this study does not look at the antibody levels at all. The study looks just at breakthrough infections in patients.
Then what is the role of Covid-19 vaccines in cancer patients?
The vaccines are certainly protective; they reduce mortality and are safe. And they ensure that when there is the next wave, patients do not have to discontinue their treatment. Treatment gaps really affect the outcomes of cancer patients.
We have seen that whenever there is an increase in the number of cases, people are very hesitant to come to hospitals, even with the Omicron wave. In fact, we were missing the diagnosis of nearly 1 lakh per month. All of this does affect the outcome and this is where the vaccine becomes important.