DR. WALKER

HERD IMMUNITY

The concept of herd immunity has assisted mankind in the past with eradication of several diseases to include smallpox, and polio. Measles was another virus on the path of being eradicated by herd immunity until the recent outbreaks in places like sub-Saharan Africa and American Samoa.

There is some discussion now as to the utility of herd immunity protecting people from COVID-19. But first what is herd immunity? Herd immunity happens in one of two ways; when enough people get a disease, recovers and then are unable to transmit disease or if there is a vaccine available to offer protection and therefore protects the vulnerable from getting it.

Essentially, once vaccinated or recovered from the disease the thought is that individuals who are now immunized act as a shield for those who have weakened immune systems or are otherwise medically vulnerable. The problem with herd immunity and Covid-19 is that there is still a myriad of unanswered questions; importantly is the question of long-term protection after COVID-19 infection.

One model suggests that for herd immunity to be protective approximately 1/2 to 2/3 of the United States population must be immune. That essentially means that between 165 and 220 million Americans must acquire the disease, recover then become immune against the virus.

One method of determining this is the R-nought/R0 formula which essentially is the basic reproduction rate of a virus. Essentially this represents the average number of people that is infected by one infectious person.

If R0 is larger than 1, then the number of infected people will likely rise exponentially. Conversely, if that number is less than 1, then there is no outbreak and the virus will likely be terminated. One model for the R0 for COVID-19 is that each infected person can infect another 2 to 3 people. But there are models that predict that the R0 is as high as 4.

The higher the R0 the greater the exponential rise of the disease, and the pandemic ensues. Essentially, it would require enough people to be protected against the virus that the viral transmission rate would be reduced enough that the virus could no longer spread to others. The other concern is that we truly do not currently understand the mutation rate of this virus.

It was only after years of people contracting the common cold and flu that we currently understand that herd immunity is ineffective against viruses with high mutation rates. That being said, we are still uncertain whether or not COVID-19 has a high mutation rate. Currently there is one new strand of COVID-19 which appears to be more contractible than the initial disease.

Additionally, the mortality rate of COVID-19 is approximately 1% but some researchers suggest the mortality rate closer to 3%, which would require more than 2 million people could succumb prior to achieving herd immunity. According to the CDC, 8 out of 10 deaths in the US from COVID-19 are people 65 and older.

People 85 years old who get the disease, have a staggering 6 to 29% ICU admission ICU. According to one article “Black people account for 25 percent of those who have tested positive and 39 percent of the COVID-related deaths, while making up just 15 percent of the general population.” In the end, the question comes down to who among us determines which 2 million people should die for us to achieve Herd immunity?