Thinking Problems - Transmission

This is a follow-up to Thinking Problems – Lab Leak.  One could have thought that, by now, the issues of COVID would have faded into the background, but no.  Misinformation about the COVID vaccine is still circulating.

In discussions with JP, there was a common claim that “they” had said that the vaccine would prevent transmission.  For example, in August 2021, JP was housebound because he was worried about a local outbreak.  I asked about his vaccine status and his reply indicated that there would have been little consolation in having a second jab if he could still spread it.  A month later he was claiming that the “initial focus was on preventing spread”.

The problem is that the issue is very complicated.  I know that I am going to overly simplify things here, but I do so with the intent of getting past an apparent blockage on the part of some of the more conspiracy minded among us.

For a virus-based disease, there is sequence of events somewhat like this:

When thought of like this, it is clear that having a vaccine cannot help with certain stages.  You are either exposed or you are not.  With infection, that’s more a question of whether you ingested the virus or not.  Here things are a bit blurry because there is you and there are your cells.  There is also the virus and there are virions.  It’s possible that a virion (one particle of the virus) got into you, but did not enter a cell (thus infecting it) before being excreted or destroyed.  Did you (the human) get infected by the virus?  You certainly got closer than if you were merely exposed to the virus (ie sitting in a room in which virions were floating around in the air that you breathed, but you didn’t happen to breathe in one).

What about if one or a few of your cells did get infected, but your immune system immediately identified the threat and destroyed the infected cells before they could set up their virus replication process?  You didn’t contract the disease, your body as a whole didn’t get infected, but you were partially infected.

What about if you did get widespread infection of cells by the virus, your immune system swung into gear mounting an effective response, but you never got any symptoms – meaning that, strictly speaking, you never developed the associated disease?  This is non-symptomatic infection, which in hindsight appears to have happened with considerable frequency.  Usually, being non-symptomatic means you are not contagious.  But not always (as the Typhoid Mary case demonstrates).

I am going to just highlight a grey area between infection by the virus and development (or contraction) of the disease.  For the purposes of this argument, I am counting disease as including the non-symptomatic who produce enough virions to be contagious.

If viruses didn’t cause disease, we probably wouldn’t care about them.  It is worth noting though that not all the symptoms of an infection are due to the pathogen (virus or bacteria) per se – some of them are the immune system fighting against the infection (fevers for example).

The job of a vaccine is to prepare the immune system for fighting a specific pathogen (or suite of pathogens).  The better prepared the immune system is, the less likely it is that the disease will take hold.  This can range from preventing symptoms entirely, making the symptoms less severe and reducing the time that it takes for the immune system to eliminate the disease.

Viruses are particularly nasty because they take over the cells of hosts and redeploy them to replicate virions.  It’s rarely a friendly take-over, with the replication machinery set to keep working until the cell bursts, releasing thousands of virions which go on to infect new cells.  Quickly, the body is riddled with virions which then get into various liquids in the body, including those in the lungs, meaning that when an infected person breathes out, there are virions lurking in droplets that we inevitably spread about us.

This is transmission in the schema above.  The virus effectively uses us to spread itself around us in a fog of about 1.5-2 metres (as is most visibly noticeable on a cold day).  But note that transmission does not mean reception (exposure or infection).

If you have a viral disease, the only way to prevent transmission is to prevent droplets getting out and to another person.  The right sort of mask, when worn properly, can do that.  Or keeping away from others (social distancing).  Or not going out in public (isolating).  The vaccine will not help you, if you already have the disease.  Your having been vaccinated will also not help you if it is not you who has the disease, it won't stop stop someone else transmitting.

What the vaccine will do is increase the likelihood, if you get virions into your body, that your immune system will prevent an infection progressing to disease, reduce the seriousness of the disease if you can't prevent it (and possibly reduce the number of virions you produce that can then be transmitted to someone else) and shorten the period in which you have the disease (and are contagious).

In that sense, the vaccine can certainly minimise spread of the disease.

But it will never prevent contagious people from transmitting the virus, nor will it necessarily prevent you developing some form of the disease if you are infected (although it's much more likely to be mild, or even asymptomatic, rather than severe).

That’s not to say that there aren’t sterilising vaccines or other treatments –that are hugely effective and prevent you from producing virions if treated.  It’s simply that the covid vaccines were never advertised as those.  The effort was all about preventing severe disease, which is why they are described as COVID-19 vaccines not SARS-CoV-2 vaccines.