Cancer patients are at increased risk of infections due to their immunocompromised state. Contributing factors include patients’ pre-morbid health, performance status, type of malignancy and treatment modalities [1]. Systemic treatment including chemotherapy, and other targeted treatment can further increase the risk of infection [2]. The World Health Organization (WHO) declared the novel coronavirus (COVID-19) outbreak as global pandemic in March 2020. Over 600 million people have been infected with unfortunately over 6 million confirmed deaths globally. Public health measures were introduced to reduce the risk of viral transmission [3]. Cancer patients were reported to have increased risk of severe covid-19 infection, mechanical ventilation and ICU admission. Furthermore, patients who had received chemotherapy or undergone surgery in the 30 days before contracting COVID-19 were found to have a higher risk of severe complications than patients who had not been treated with chemotherapy or surgery. Other studies reported that an anti-cancer treatment within 14 days of COVID-19 infection was a risk factor for acute respiratory distress syndrome, septic shock, and acute myocardial infarction [4]. Kuderer et al reported that 30-day all-cause mortality was high among cancer patients with covid-19 infection [5].

There were also concerns of significant delay in cancer screening, diagnosis, treatment and surveillance ultimately leading to increased risk of cancer-related morbidity and mortality [9]. In general, anti-infective vaccinations have been shown to be safe and effective in cancer patients. However, reduced protective effects may occur in patients undergoing certain systemic anti-cancer treatments. Ideally vaccination should be administered before the commencement of systemic therapy, although vaccination during the treatment may be implemented [10,11]. Several clinical trials were initiated globally to develop and evaluate the safety and efficacy of different covid-19 vaccines.

Polack FP et al reported results of multinational, placebo-controlled, observer-blinded, pivotal efficacy trial, evaluating the Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine which conferred 95% protection against Covid-19 in persons 16 years of age or older [13]. FDA authorised emergency use of Pfizer-BioNTech COVID-19 vaccine on August 23, 2021 [8]. Since then, several covid-19 vaccines have been approved including, Moderna COVID-19 Vaccines, Janssen COVID-19 Vaccine and Novavax COVID-19 Vaccine. Major health organisations across the world recommended emergency use of covid-19 vaccination. However initially there was a lack of safety and efficacy data for covid-19 vaccination in cancer patients as they were generally excluded from these trials.

It was noted that the rate of seroconversion was significantly lower following only one dose of an mRNA vaccine hence the importance of vaccination completion and booster was advised for cancer patients [12]. VOICE and CAPTURE studies reported significantly inferior antibody response after only one dose of the vaccine, However, after full vaccination above 80% patients with cancer developed neutralising antibodies [13,14]. In a real-world study of patients with cancer, only 29% of patients had an antibody response after the first vaccine dose, compared with 84% of controls (P< 0.001). However, after the second dose seroconversion rate was 86% [15].

There remains a subgroup of cancer patients with impaired immune response following anti-SARS-CoV-2 vaccination especially haematological malignancies compared with patients with solid tumours [16]. In particular a lower seropositivity rate following vaccination was reported for patients treated with cytotoxic chemotherapy compared with other cancer patients [17].

In practice it is important to assess the clinical effectiveness of vaccination such as rates of infection, COVID-19 disease severity and mortality. Embi et al. reported that mRNA vaccine effectiveness against COVID-19–associated hospitalisation was clinically significant among immunocompromised patients but lower than immunocompetent patients [18]. Another study concluded that vaccinated patients with cancer achieved clinical effectiveness of 57% for patients on chemotherapy, 76% for those on endocrine therapy and 85% for those not receiving systemic therapy [19].

Hence guidelines from major health organisations included cancer patients amongst the high-risk population and recommended vaccination of cancer patients as a priority [6,7]. DAHC was one of the first organisations in the region who implemented these recommendations very early on during the pandemic [8].

We recommended that the majority of our patients undergo Covid-19 vaccination after thorough counselling and reassurance. Majority of the patients (91%) received Pfizer Bio-NTech vaccine at DAHC, and the vast majority completed at least 2 doses of the approved vaccine. We also recommended Booster vaccine to our patients.

Our study concluded that there was significant covid-19 infection-related mortality among unvaccinated older cancer patients as was shown in the initial reports during the pandemic [4,5]. Earlier studies had shown lower seroconversion following one dose of covid-19 vaccine which improved after the 2nd dose, however clinical significance of vaccination was not known.

We noticed significant differences in all-cause mortality in covid-19 infected patients in the vaccinated and unvaccinated group. There was higher mortality amongst unvaccinated groups. Covid-19 vaccine reduced the risk of mortality amongst covid-19 infected patients. However, the risk of acquiring Covid-19 infection was similar between the two groups.