Herd Immunity-Covid19 update 10-16-20
In the last 2 weeks there have been several Covid related stories. One of these stories is the argument that society should seek to get herd immunity by isolating the most vulnerable individuals and letting the rest of the population resume normal activities without restrictions. Specifically, face masks and social distancing would not be encouraged. Hand washing and staying home when ill would be the only recommended actions.
The proponents of this plan like to point to Sweden as a model. Specifically, Sweden did not shut down like the rest of the world back in March, and they assert that Sweden did as well or better than any other country in terms of infections and deaths while not suffering as much economically.
However, the data does not support the Swedish model. As of late September, Sweden had 57 deaths per 100,000 people, while neighboring countries who did take actions to limit activities had far fewer deaths. Denmark only had 11 deaths per 100,000, Finland 6 deaths per 100,000 and Norway 5 deaths per 100,000. Sweden also suffered through an economic downturn. In addition, the percent of Swedes who have antibodies to Covid19 remains low, and nowhere near the numbers needed to assure herd immunity.
It is estimated that up to 22% of New Yorkers have antibodies to Covid19, yet the number needed for herd immunity is most likely 70% or higher. Furthermore, many millions of people would need to get infected in New York City to achieve herd immunity and the death rate would range between 15,000-30,000 additional people. So far New York City has had just under 24,000 deaths.
Another equally distressing factor is the unknown duration of immunity from a Covid19 infection. While thankfully case reports of recurrent infections with Covid 19 are relatively uncommon, no one knows how long someone will remain protected. Only time will tell.
More problematic is figuring out who is truly vulnerable. Older adults are not necessarily more likely to get Covid19, yet they are more susceptible to get seriously ill if they do become infected. In addition, it is estimated that about 45% of the US population has some preexisting health condition that may increase the risk of a serious infection, and this includes people of all ages.
Clearly, shutting everything down is not the answer, yet going to the other extreme and opening everything up without restriction is also not an acceptable solution. Until we have a vaccine, prudent interventions and restrictions in areas with Covid 19 activity make the most sense. These include mask wearing and social distancing and when case numbers go above a certain threshold, selective closures and restrictions to contain the outbreak. We saw this done successfully at the University of Arizona last month
Finally, not everyone has a full and complete recovery from Covid 19, and residual neurological, pulmonary, and cardiac issues do affect a significant minority of individuals. I will discuss these more in my next message. Take care and have a good week.
Jeff Mayer, MD