What have the results of the vaccine trials told us about COVID-19 infection?

The uniform success of the first three COVID-19 vaccine trials has been a much-appreciated outcome. While the remarkable success of the RNA based vaccines and the relative success of the adenovirus vaccine are welcome, the results from these clinical trials probably tell us as much about the COVID-19 infection itself as the efficacy of these vaccines.

The efficacy of the vaccines suggests that while COVID-19 is an easily transmissible infection, it is relatively low in virulence and pathogenicity. What does this mean? 

Easily transmitted but not highly virulent!

The ease in transmissibility comes from the fact that COVID-19 is relatively easy to spread via aerosols, especially in super-spreader situations where there is a high level of virus in the air. This means that the virus is very effective in its ability to move from person to person. This is clearly demonstrated globally by the scope and the rapid spread of this pandemic. 

What was confusing was the fact that the majority of people infected with this virus, even in the elderly or high-risk groups, did not get terribly ill from the infection. Even in individuals over the age of 70, the infection fatality rate from COVID-19 is 5.4%. Remarkably, almost a year into the pandemic the reasons for this remain unclear. 

Some have hypothesized that the virus only caused severe disease in genetically susceptible individuals. This suggested that people who got seriously ill from COVID-19 had immune problems that kept them from effectively fighting the virus. There were studies that showed that some young people who died from COVID-19 had specific, genetically defined problems in responding to RNA viruses like COVID-19. This made sense in many ways and suggested that SARS-CoV-19 is not highly virulent, in other words, not very efficient in harming the immune intact human host. 

The vaccine studies now suggest that even a small amount of immunity is very protective against COVID-19. To have a vaccine that is essentially totally protective against this infection in 95% of the population is remarkable and suggests that most people have evolved over thousands of years to deal with coronavirus infections. Since infections occur frequently with other, seasonal coronaviruses, it is not surprising that humans have evolved their immune systems to deal with this class of viruses. You just need to give the immune system a bit of a head start with a vaccine.

Therefore, in a “War of the Worlds” scenario, our annual battles with seasonal respiratory infections have provided us with the ability (as a species) to survive COVID-19. It is a comforting and somewhat edifying concept, but it does not answer an unsettling question. Why did so many people with relatively minor, chronic illnesses (obesity, hypertension, diabetes) become deathly ill from this disease? Is there some unknown immune problem that comes from these illnesses? Are there problems with lung or immune function from these underlying conditions that are worse than we understand?

We owe it to the millions of people who have died and will die from COVID-19 to get a better understanding of the effects of chronic, degenerative illness on human physiology. It will assure they have not died in vain and help people with these diseases survive the next pandemic.

Published by jbakerjrblog

Immunologist, former Army MD, former head of allergy and clinical immunology at University of Michigan, vaccine developer and opinionated guy.

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