COVID-19 vs flu

By now, everyone knows that the early claims by Trump and his administration that COVID-19 is just like the flu, would go away when the weather gets warm and was no more deadly were just lies. Not merely false, but lies, since Bob Woodward showed that Trump knew otherwise at the time. But somehow, people still seem to want to compare SARS-CoV-2 to the flu virus, both in terms of the epidemiology and in terms of the value of vaccination.

There are valid concerns about the rate of viral evolution in terms of immunity. Immunity to a natural infection may or may not confer immunity to the same virus in the future if the virus evolves variants that escape immune surveillance. Same with vaccines: a vaccine may not be protective in future years to variant viruses. This is a huge problem with flu. Not so much with smallpox, yellow fever, polio, measles, mumps, chicken pox, rubella or tetanus.

With viral pandemics, it is important to understand the sources of variation and the selection pressures on the virus. While data on SARS-CoV-2 itself are limited, there are other coronaviruses from which we can gain important insight.

Influenza viruses are RNA viruses. The replication mechanism for RNA genomes is more error-prone than for DNA genomes. HIV is also an RNA virus (albeit a different class of virus) and this error-prone replication explains how drug-resistant AIDS arises. But things are even more challenging with flu virus, because their RNA genomes are segmented into 7-8 pieces, which can be shuffled in different combinations in an infected cell as new virus particles are assembled. This variable provides an important part of the mechanistic explanation for why new flu pandemics can arise and why the annual flu vaccine may only provide incomplete and transient protection.

Coronaviruses also have an RNA genome, but it is a single molecule, so the reshuffling that happens with flu virus doesn’t occur. Since the COVID-19 pandemic began in January, a huge amount of data have accumulated on the sequence variants in genomes of clinical samples all around the world. So far, it doesn’t look like the virus is evolving rapidly, even though the number of virus particles worldwide is immense and the rate of new infections is breathtaking. But there has been one clinically significant variant identified that does seem to render the viruses that carry it more infectious. So far, this variant doesn’t seem to make a difference to disease progression, nor would it affect the current vaccines.

“There is no evidence that a coronavirus with the 614G mutation causes more severe symptoms, kills more people or complicates the development of vaccines. Nor do the findings change the reality that places that quickly and aggressively enacted lockdowns and encouraged measures like social distancing and masks have fared far better than the those that did not.” https://www.nytimes.com/2020/11/24/world/covid-mutation.html?action=click&module=Top%20Stories&pgtype=Homepage&fbclid=IwAR1tm-FZlPlraiMFfcMwBxRkApk77Z7sS8z9e9AgBj8RH-X_QEykWwcfSss