Introduction

Influenza, or flu, is a common seasonal illness caused by a viral infection in the respiratory system. The flu causes symptoms such as fever, aching, and excess phlegm in the nose and throat. Typically, flu occurs in epidemics, affecting thousands of people in a community at the same time.¹

Cancer is a devastating disease attributed to uncontrollable cell division. Common treatments for cancer include chemotherapy, targeted cancer drugs, radiotherapy and high-dose steroids. These treatments may cause the immune system, which protects us from infections such as flu, to become weak and inefficient. This is due to cancer treatments reducing the number of white blood (immune) cells being made in the bone marrow. As white blood cells play major roles in the immune system and immune responses, their potency is also decreased.² 

Understanding the interaction between cancer treatments and the immune system is crucial in appreciating the increased vulnerability of cancer patients to infection, its implications for their health, and the best treatment protocols. This article aims to explore the impact of the flu on cancer patients, prevention and management of the flu and common complications seen in these patients.   

Impact of influenza on cancer patients

Increased risk of influenza infection

Cancer treatments are commonly associated with immunosuppression, preventing the immune system from effectively dealing with invasive pathogens. These therapies target any cell that is rapidly growing, as this is a key characteristic of cancer cells. Since the immune system must rapidly produce cells and expand to defeat invading pathogens, it often falls victim to cancer therapies. Cancer therapies reduce the number of white blood cells being made in the bone marrow. These white blood cells, also called lymphocytes, are essential in effective responses to infections, such as flu, as they both recognise and destroy the cause of infections. Without new generations of lymphocytes, a weaker response to the flu occurs and complications are much more likely to occur.²

Clinical presentation of influenza in cancer patients

The flu can be more serious in cancer patients, due to their weakened immune systems. Typical flu symptoms include fever, cough, sore throat, body aches, fatigue, and headaches. However, cancer patients may show atypical symptoms such as confusion, general weakness, or low-grade fevers, instead of the classic high fever and respiratory symptoms. They may also have milder or unusual symptoms, making it harder to diagnose the flu early.

The complications of flu in cancer patients are often more severe, leading to serious issues including pneumonia (lung infection), growth or spread of their cancer, and other infections. Since their immune systems are already compromised, cancer patients are at higher risk for these complications, which can lead to hospitalisation or even death.

The severity of the flu in this population is generally higher. Flu infections can prolong recovery times, cause delays in cancer treatment, and increase the chances of severe complications. Early diagnosis and treatment, including antiviral medications, are critical to managing the flu in cancer patients to reduce the risk of complications. Vaccination and infection prevention measures are also very important for this vulnerable group.³

Impact on cancer treatment and management

When a cancer patient contracts the flu, their immune system is further weakened, which can lead to delays in scheduled treatments like chemotherapy or radiation. This is because cancer treatments often reduce white blood cell counts, making patients more susceptible to infections. Continuing treatment while the body is fighting the flu can increase the risk of severe side effects or worsen the infection. As a result, doctors may temporarily stop or adjust the cancer treatment plan until the patient recovers from the flu, which can disrupt the overall treatment schedule.⁴

Flu can also interact with ongoing cancer therapies. Chemotherapy, immunotherapy, and other cancer treatments can suppress the immune system, making it harder for the body to fight the flu. Additionally, antiviral medications used to treat the flu might interfere with the activity of cancer drugs, potentially reducing their effectiveness or increasing their toxicity. This makes managing both the flu and cancer more complex, requiring careful monitoring by healthcare providers to balance both conditions without causing harm.

Vaccination and preventive measures

Influenza vaccination for cancer patients

Vaccination against the flu is strongly recommended for cancer patients, especially those undergoing chemotherapy or other treatments that weaken the immune system. Most cancer patients are advised to receive the annual inactivated flu vaccine, as it is safe for those with weakened immune systems. The live nasal spray vaccine is not recommended for cancer patients due to potential safety concerns. Family members and caregivers should also get vaccinated to help protect the patient.

Flu vaccines are generally safe for cancer patients, but their efficacy may be lower compared to the general population due to the weakened immune response. Even though the vaccine may not work as well, it can still provide important protection, reducing the severity of flu symptoms and lowering the risk of complications like pneumonia. Studies show that vaccinated cancer patients experience fewer flu-related complications and hospitalisations.⁵

Timing is crucial for maximising vaccine effectiveness. Experts recommend that cancer patients receive the flu vaccine before starting chemotherapy or other immunosuppressive treatments if possible. If a patient is already undergoing treatment, the vaccine can still be given, but healthcare providers will time it to avoid periods of extremely low white blood cell counts (neutropenia), which can reduce the vaccine’s effectiveness. Ideally, vaccination should occur during periods when the immune system is relatively stronger.

Other preventive strategies

Personal hygiene plays a big role in preventing the transmission of the flu. Frequent handwashing with soap, using hand sanitiser, and avoiding touching the face can help reduce infection risks. Wearing a mask in crowded places and covering coughs and sneezes also prevent the spread.

Infection control at home involves regular cleaning of frequently touched surfaces like door handles and phones. Cancer patients should also avoid high-risk environments, such as crowded public spaces or being around sick people, to lower the chance of flu exposure. Family members and caregivers should follow these same precautions to protect the patient.

Management of influenza in cancer patients

Diagnosis and early detection

Symptoms of the flu overlap with the side effects of cancer treatments or can be mistaken for other infections common in cancer patients. For example, chemotherapy can cause fatigue and low white blood cell counts, mimicking flu symptoms. Additionally, cancer patients are prone to bacterial infections, which may present with similar signs. It’s important for healthcare providers to distinguish between the flu, other infections, and treatment side effects to ensure proper management.⁶

Rapid and accurate diagnosis is essential in cancer patients. PCR (polymerase chain reaction) tests are commonly used to detect the flu because they are more sensitive in immunocompromised patients compared to rapid flu tests. Early diagnosis allows for timely antiviral treatment, which can reduce the severity of the illness and prevent complications. Since cancer patients may not show typical flu symptoms, diagnostic testing is particularly important to avoid misdiagnosis and to promptly manage any flu-related issues.

Antiviral therapy

For cancer patients, oseltamivir (Tamiflu) and zanamivir (Relenza) are the most commonly recommended antivirals for flu. These medications work by inhibiting the flu virus from spreading in the body. They are generally safe for cancer patients and can help reduce the severity and duration of flu symptoms.⁷

Antiviral treatment is most effective when started within 48 hours of flu symptoms. For cancer patients, early antiviral use reduces the risk of severe complications, such as pneumonia. Even if started later, antivirals can still provide benefits, particularly in immunocompromised patients, decreasing the severity of the illness.

Supportive care and symptom management

In cancer patients with influenza, fever and pain can be managed using over-the-counter painkillers such as ibuprofen, under medical supervision due to potential drug interactions with cancer treatment causing side effects. Keeping hydrated, resting, and using lozenges for sore throat can also help. Clinical monitoring is essential in preventing any complications from developing. If the patient develops persistent fever, shortness of breath, or chest pain, medical advice must be sought.

Adjustments to cancer treatment

After contracting the flu, cancer patients may temporarily cease to prevent further weakening of the immune system and the best recovery for the patient, with fewer complications. Often, medical professionals who specialise in oncology (cancer) and infectious disease liaise to formulate a care plan suited to the patient's needs.

Complications

Influenza-related complications

The most common complications for cancer patients often affect the respiratory system, including pneumonia, bronchitis and acute respiratory distress syndrome. These conditions can become serious, requiring hospital monitoring, oxygen therapy and, in the most extreme cases, ventilator support.³ Pre-existing complications of cancer can be exacerbated by the flu, prolonging recovery. 

Drug interactions and side effects

Antiviral drugs, used to treat the flu, and cancer treatments can interact, sometimes increasing toxicity. This increase in toxicity can cause a multitude of nasty side effects. Dose adjustments can prevent drugs from worsening illness. However, if side effects do occur, it is important for medical professionals to adjust the treatment plan as soon as possible for the best disease outcome. 

Summary

• Cancer treatments like chemotherapy weaken the immune system, increasing susceptibility to influenza and complications like pneumonia, as the body struggles to produce new white blood cells to fight infections
• Flu can cause delays or modifications in cancer treatment due to further immune suppression. Antiviral drugs may interact with cancer therapies, requiring careful management
• Annual inactivated flu vaccines are recommended for cancer patients, but their efficacy may be lower. The timing of vaccination is crucial to maximise effectiveness and avoid periods of low immunity
• Good hygiene, like frequent handwashing and avoiding high-risk environments, is essential to reduce flu exposure. Family members and caregivers should follow these measures too
• Early diagnosis via PCR testing is important for flu management in cancer patients. Antiviral medications like oseltamivir and zanamivir are recommended, with the best outcomes when treatment starts within 48 hours of symptom onset
• Cancer patients face severe flu-related complications, including pneumonia. Drug interactions between antivirals and cancer medications can increase side effects, necessitating dose adjustments and coordinated care