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Background: COVID-19 is an ongoing pandemic. As of 11 May 2020, there are 4 013 728confirmed cases and 278 993 deaths. Smoking has been named as one possible factor regardingillness progression and severity. Aim: The aim of this systematic literature review is to examine if smokers are more at riskconsidering disease severity. Methods: This is a systematic literature study using the PubMed database. Inclusion andexclusion criteria were specified by using the PICOS format. Free text words and MeSH wordswere combined to create a search plan. The search was conducted twice, 26 April 2020 and 12May 2020. Full text articles were examined for eligibility by using inclusion and exclusioncriteria. An estimation of bias was conducted by using the MINORS criteria. Result: A total of seven articles were included. Of those, 5 reported a statistically significantrelationship between smoking and disease progression or death. Of these, 4 articles foundstatistical significance when correcting for confounders (hypertension, COPD, ischemic heartdisease, cardiac insufficiency). Conclusions: The result of this systematic literature review suggests that smoking enhancesthe severity of COVID-19. Due to the limited number of patients combined with a narrowgeographic area being studied, more research is needed to further evaluate and establish therelationship between smoking and COVID-19.

The rapid development, approval, and production of vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in less than 1 year after the first reports of a new infectious disease was a real game changer, providing 80%–90% efficacy in preventing severe etiopathologies of the coronavirus disease 2019 (COVID-19). These vaccines induce an immune response against the SARS-CoV-2 spike (S) protein located on the surface of the virus particle. Antibodies (Abs) recognizing the S-protein can inhibit binding of the virus via the S-protein to the angiotensin-converting enzyme-2 (ACE-2) receptor expressed on different human cells, especially when these Abs bind to the interaction site, the so-called receptor-binding domain (RBD). We have expressed the RBDs of wild-type SARS-CoV-2 and five variants of concern (VOCs) to test the immune response in people before vaccination with mRNA vaccines BNT162b2 and mRNA-1273 and after up to three vaccinations using in-house ELISA and inhibition assays. The methods of both assays are provided. Both vaccines initiated similarly high IgG titers after two vaccinations against the wild-type and even two VOC-RBDs (alpha and delta) and strongly inhibited the corresponding RBD-ACE-2 binding. The IgG titers and inhibition of ACE-2 binding were lower for beta and gamma RBDs and much lower for omicron RBD. The third vaccination after 6 months strongly increased both the IgG titers and the neutralizing effect against all variants, especially for omicron, leading to 63% ± 13% neutralization potential. Importantly, neutralization linearly increased with the IgG titers.