A Cautionary Tale
We are people—and people understand and remember stories far better than they remember (or understand) statistics, however reliable the statistics may be. What follows may serve as an instructive anecdote.
A friend and his wife, we’ll call them John and Marti, had breakfast at a picnic table outside about two weeks ago with another couple. All four of them were fully vaccinated (two doses) early this year (about six months ago). Husband sat opposite husband and wife opposite wife. The husband of the second couple has trouble hearing, so some of the conversation was carried on fairly close face-to-face between the two men. Five days later the husband of the second couple called John to report that he had just tested positive for Covid-19 on a test performed preventively in anticipation of visiting a vulnerable relative. John and Marti promptly got tested (with a sensitive hospital-based PCR test). John’s test was positive for evidence of Covid-19 virus, Marti’s was negative. John went into quarantine, concerned that he might pass the virus on to someone vulnerable.
The upshot? Both men (and their test-negative wives) remain entirely asymptomatic, both men have quarantined. Both, were it not for the initial requested test, might have spread Covid-19 to people vulnerable to becoming gravely ill or dying from the disease (unvaccinated people being much more vulnerable).
Clearly, the virus that causes Covid-19 can be spread under some circumstances, even outdoors, from one fully vaccinated individual to another. But there’s more. John is an retired physician with an inquisitive scientific mind. He had acquired a box of home antibody tests months ago. John and Marti, soon after their second shot early this year, tested themselves for anti-Covid-19 antibodies. Both tests showed that John and Marti had made IgG antibodies in response to vaccination. John and Marti did another antibody test right after they found out their friend had tested positive. Marti’s test still was strongly positive for IgG antibodies to Covid-19; John’s test was only very weakly positive. (Bear this in mind, though: waning IgG does NOT mean that John’s immune system has no memory of vaccination. The immune system typically retains a biochemical memory of the immune response it once mounted and is able to ramp up antibody production much faster than a “virgin” immune system. Immune memory is like having the factory still there, but sitting idle, as opposed to having to build a whole new factory.)
Like all good scientific data, this story raises more questions. Was John’s immune system just a bit less robust than Marti’s in maintaining IgG expression or had Marti gotten a “booster exposure” of virus since her vaccination to which her immune system ramped up IgG expression? Was John’s relative lack of IgG the reason the virus (presumably transmitted by his breakfast friend) could replicate in John’s nose? (We don’t really know whether or not there was sufficient virus replication in John’s nose to actually transmit the virus to someone else.)
The take home message is clear, however: At least some totally asymptomatic individuals vaccinated more than six months ago can carry and transmit the virus that causes Covid-19 (now most likely the delta variant). If John’s immune system hadn’t been forewarned by vaccination (i.e. his immune system were “virgin” to the virus) this unmasked, outdoor breakfast encounter might have had a grievous result.
If you’re vaccinated you still need to be careful for the sake of others (and, at a lower statistical likelihood of severe disease, for your own sake). Wear a mask indoors and in selected outdoor settings. If you’re not vaccinated, GET IT DONE. If you think you’ve had or actually had a test-positive Covid infection already, get a vaccination anyway. There are increasing reports that vaccination offers much better protection against the delta variant than does natural infection with one of the earlier strains.
Keep to the high ground,
P.S. Booster vaccination is a topic for another day.