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Several studies found only weak signs of adaptive evolution early in the COVID-19 pandemic. [c] Kang et al. wrote that SARS-CoV-2 had exhibited relatively little genetic variation by 2021. [47] Tai et al. wrote that population expansion rather than positive selection explained the mutation frequency spectrum during the early pandemic. [49]
Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the coronavirus SARS-CoV-2. In January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic . The symptoms of COVID‑19 can vary but often include fever, [ 7 ] fatigue, cough, breathing difficulties , loss of smell , and loss of taste .
SARS-CoV-2 is the seventh known coronavirus to infect people, after 229E, NL63, OC43, HKU1, MERS-CoV, and the original SARS-CoV. [105] Like the SARS-related coronavirus implicated in the 2003 SARS outbreak, SARS‑CoV‑2 is a member of the subgenus Sarbecovirus (beta-CoV lineage B). [106] [107] Coronaviruses undergo frequent recombination. [108]
Long COVID is an often severe multisystem disease with a large set of symptoms. There are likely various, possibly coinciding, causes. [76] Organ damage from the acute infection can explain a part of the symptoms, but long COVID is also observed in people where organ damage seems to be absent. [77]
The latest symptoms of COVID-19 are tied to new dominant subvariants – BQ.1 and BQ.1.1 – which now comprise the majority of cases reported in the U.S.
Experts generally believe that symptoms of COVID-19 have become less severe over time, Dr. Otto Yang, professor of medicine in the division of infectious diseases and of microbiology, immunology ...
However, the COVID-19 of 2023 isn't the same as the COVID-19 of 2019 and 2020—the variant that uprooted our lives. Doctors share that the disease has evolved and so has population immunity.
SARS was a relatively rare disease; at the end of the epidemic in June 2003, the incidence was 8,422 cases with a case fatality rate (CFR) of 11%. [5] No cases of SARS-CoV-1 have been reported worldwide since 2004. [6] In December 2019, a second strain of SARS-CoV was identified: SARS-CoV-2. [7]