Effective protection against COVID-19 disease was crucial during the pandemics for patients with solid cancers receiving systemic treatment, as they are significantly more at risk of a more severe course of the disease and death in the event of SARS-CoV-2 infection. Patients with malignancies on active treatment were not included in the registrational clinical studies of the efficacy and safety of vaccines against COVID-19, so questions about the immunogenicity, efficacy and safety of vaccination against COVID-19 in this population remain poorly elucidated.
In the first part of the research, we focused on the immunogenicity achieved after solid cancer patients received mRNA vaccines against SARS-CoV-2 simultaneously with their systemic treatment by determining the level of anti-SARS-CoV-2 S1 IgG antibodies in serum at predetermined time points. The results was also compared with the general population, which was vaccinated according to the same protocol and gave blood at similar time points. We demonstrated that the development of anti-SARS-CoV-2 S1 IgG antibodies in patients with solid cancers is comparable with respect to the general population, that antibodies increase appropriately after the completion of the entire primary course of vaccination (after two doses of the vaccine), that there are differences according to the systemic therapy received and that antibodies begin to decline universally three months after completion of vaccination, more so in patients with solid cancers than in the general population. We also evaluated immediate adverse evnets after vaccination (24-48 hours after receiving the first and second doses of the vaccine) and did not find significant differences compared to the general population.
In the second part of the research, we focused on the decline in the level of anti-SARS-CoV-2 S1 IgG antibodies, which occurs three and six months after the completion of the primary vaccination and on the increase in the case of receiving the third booster dose of the vaccine. We have demonstrated that the decline in the level of anti-SARS-CoV-2 S1 IgG antibodies is significant and that in the case of the third dose of the mRNA vaccine against SARS-CoV-2 it increases by more than 20 times. After the third dose, anti-SARS-CoV-2 S1 IgG antibody levels were again comparable to the general population that also received a third dose of the vaccine.
In the third part, we focused on the safety of mRNA vaccines and the incidence of infections after vaccination. We demonstrated that mRNA vaccines against SARS-CoV-2 are safe even in the population of patients with solid cancers on systemic therapy, we recorded only one serious long lasting adverse event, which could be attributed to both vaccination and oncology therapy. We found that breakthrough infections do occur in about a third of vaccinated patients, but they are mild or moderate and mostly do not require hospitalization and intensive treatment. Of all vaccinated patients, we recorded two deaths due to concurrent infection with SARS-CoV-2 and a critical course of the COVID-19 disease. Vaccination also did not affect the time to disease progression or death from the underlying cancer.
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