If you think you may have had Covid-19 earlier than most it is of course entirely possible, even going back to January of this year, prior to that though you may well have encountered a different virus but of the same coronavirus family.
Given the evidence that even if we haven’t had Covid-19 half of us may still have some protection provided by T cells is in fact somewhat reassuring. The question that remains though is where might that come from. It was suggested that it might come from exposure at levels to low to infect but sufficient to prompt our bodies to respond with T cells. The fact is we don’t yet know the mechanism but it could be that having had a previous coronavirus infection but not the current one, might also trigger T cell production.
Are there any candidates for this and is it likely we have already been infected?
The answer seems to be that most of us could well have ‘bumped into’ a corona virus. There are four HCoVs that fit the bill; HCoV 229E, NL63, OC43, and HKU1 these are all viruses that are endemic worldwide and in fact account for 10% to 30% of upper respiratory tract infections in humans.
Of these 4 coronavirus 229E and OC43 are the most common with OC43 most likely to invoke hospitalisation causing about 15% of patients to be admitted.
Which coronavirus warrants a vaccine?
Of the types of virus circulating the one most likely to cause a serious one is probably OC43. A serious case of this can cause pneumonia. It is found in both cattle and humans but its lethality is low so it has never caused us a big population. In fact that is why Covid-19 is such a problem for us globally at the moment. SARS (2003) was a far more dangerous disease if caught. That very fact that it was lethal meant that once isolated it was unable to propagate as it destroyed the host as a result the outbreak died out.
Using OC43 as an example it persists because it does not cause a big health problem, as a result developing a vaccine is low priority. On the other hand Sars Cov-2 the virus that causes Covid-19 can exist symptomless in some patients yet cause viral pneumonia and attack multiple human organs in others. In that respect it has found a perfect method of survival. This makes it a perfect candidate for a vaccine. There are currently approximately 70 different laboratories searching for one around the world.
If we inadvertently have some Covid-19 immunity it seems that OC43 or 229E are most likely to have been the virus that triggered out T cell production given that they are the most common globally.
We have seen how of several viral epidemic the current Sars Cov-2 virus is the virus that has prompted us to urgently seek a vaccine. The earliest candidate for this is the Oxford Vaccine Group we await trials to see if it is both safe and effective.