Booster third dose of SARS-CoV-2 vaccine effectively lifts the waning immune response of solid cancer patients

ABSTRACT

Background: Since cancer patients (pts) are at increased risk of severe morbidity and mortality due to COVID-19, SARS-CoV-2 vaccination is crucial to prevent severe disease course. The efficacy and longevity of vaccine protection, however, is still in question. Methods: In this prospective observational study we assessed immunogenicity of cancers patients on active treatment for solid cancers in two Slovenian Oncology Centres receiving SARS-CoV-2 vaccine by detection of anti-SARS-CoV-2 S1 IgG antibodies in serum;before, after first and second dose, 3 and 6 months (mo) after complete primary course of vaccination and 1 mo after the 3rd booster dose. Samples with ≥ 175 ng/ml were considered positive. Results: There were 125 pts included in the study, 112 completed the primary course of vaccination with 2 vaccine doses and 34 received the booster 3rd dose. Out of 34 pts receiving booster 3rd dose, the majority received mRNA based vaccines (88%) for the primary course of vaccination and all patients received mRNA based vaccines for the booster 3rd dose. Median time from 2nd to booster 3rd dose of vaccine was 6.75 mo, median age of pts was 66 yrs and 59% were male. Patients were receiving chemotherapy (ChT), immune checkpoint inhibitors (IO) or targeted therapy (TT) in 9%, 56% and 35%, respectively. They achieved seroconversion in 94% after the 2nd and in 97% after the 3rd booster dose. Overall, the median anti-SARS-CoV-2 S1 IgG titer was 11,191 ng/ml (mean 25,394;range 0 - 100,000) after complete primary course of vaccination and 1892 ng/ml (mean 6413;range 0 - 72,000) 6 mo after, P < 0.0001. However anti-SARS-CoV-2 S1 IgG antibodies increased significantly after the 3rd booster dose with median antibody value 51,310 ng/ml (mean 51,787;range 0 - 100,000), P < 0.001. Only one pt in this group got infected with SARS-CoV-2 and had a mild disease course. Conclusions: Cancer pts treated for solid malignancies achieve a high rate of seroconversion through the primary course of vaccination. However, significant waning of immunity against SARSCoV-2 is observed 6 months thereafter, which can be potentiated with additional 3rd booster dose of vaccine.