Table 7 lists the keywords with high burst values in the last 3 years, which were ranked in descending order according to their burst values as coronavirus (8.87), ACE2 (7.34), SARS coronavirus (6.69), circulating tumor cell (6.48), pneumonia (5.5), cytokine storm (5.2), citrullination (5.13), prevalence (4.89), neutrophil to lymphocyte ratio (4.83), and cancer (4.61). Here, ACE2 is linked to pneumonia.