Dilemma Of Immunity

 

While we await the development of  vaccines for SARS-CoV-2 virus here are a few things to consider. First, will this virus be very much like the influenza virus meaning will it have a yearly variation or mutation requiring a new vaccine every year ?  The answer to this is very likely “yes” since in many respects this virus is like the influenza virus.

Second, how effective will the vaccine be? There are likely to be several different variations of this vaccine produced in the U.S. and elsewhere. It is very likely that we will not know for quite some time which will be most effective.

Third, there is the whole question of herd immunity. Most epidemiologists would agree that anywhere between 40-60% of a given population has to be immune either by prior exposure and subsequent immunity (so-called “naturally acquired immunity”) or immunity acquired through immunization. Since this virus is highly contagious, it is likely that the percentage of immune individuals in a society would have to be on the higher side in order to prevent or limit the likelihood of epidemic spread. Remember that in order for the virus to survive it needs to propagate. It does so by infecting the cells of a susceptible individual, replicating in those cells, spreading to other cells in that individual, and then moving on to infect other individuals in a community as the infected individual sheds viral particles one way or the other.

The fourth point to consider is the following, and herein the lies the dilemma. If we acknowledge that we need 40% to 60% of the population as a minimum to be be immune either by vaccination or naturally acquired infection in order to stop the spread of the virus, then by limiting naturally acquired infection by social distancing we may actually be increasing the susceptibility of our population as a whole to the virus as time goes on especially if the vaccines which we are banking on fail to provide the degree of protection that we anticipate. If these things happen, then we may actually end up prolonging the pandemic rather than shortening it. Remember the Spanish Flu epidemic of 1918-1919 occurred in two waves and only stopped when enough people world wide had acquired the infection and developed immunity. There was no vaccine at that time. Presumably as this happened the virus had fewer hosts to invade and within which to replicate.  As replication decreased there was less virus being shed into the environment so fewer and fewer people came into contact with the virus gradually allowing for its extinction and thereby putting an end to the Spanish Flu pandemic.  Either something of that kind happened or there was a spontaneous mutation of the virus which made it less lethal and infectious. 

This is not say we should not be working vigorously on vaccines for SARS CoV-2. We should definitely be doing so, but keep in mind that naturally acquired immunity may really be what saves us in the long run. This is essentially the route that Sweden has taken in allowing herd immunity to take place in an albeit partially controlled manner. They did not go into a draconian lockdown, but encouraged social distancing to minimize rate of exposure so as not to overwhelm their health care system all at one time. It seems to be working for them although some would disagree with their approach and results. Only time will tell whether their approach really did work for them and whether it is applicable to other countries around the world. Each country and population may be different.  There may not be a “one size fits” all approach that will ultimately work for the entire world. In the meantime work on a vaccine, or vaccines continues, as does the work to find therapeutics both to prevent viral replication and to treat the destructive  inflammatory processes caused by the infection itself. 

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