COVID-19 Herd Immunity



Day 123: Stay Safe Minnesota

Research experts say that establishing covid-19 herd immunity should not be the ultimate goal but the byproduct of vaccines & other measures.

The term Herd immunity is defined as “the indirect protection from infection conferred to susceptible individuals when a sufficiently large proportion of immune individuals exist in a population.”

More than 4 million peoples are infected with covid-19 virus, according to the Johns Hopkins database. This makes us wonder whether we have achieved some level of herd immunity to help reduce the spread of the pandemic. But some experts told to the Healthline that “we’re not even close. To get there, we would need 60 to 70 percent of the population to get an infection”.

What we do know is that the majority of Americans have not been infected. We’re very, very far from the majority. There are hot spots where the outbreak has been heavier, but even in the most heavily exposed places we know about so far, nowhere, no city has gotten anywhere close to herd immunity.

Gypsyamber D’Souza, professor of epidemiology and international health at the Johns Hopkins Bloomberg School of Public Health in Maryland (source: Healthline)

Concepts of Heard Immunity

In a recent study Herd Immunity: Understanding COVID-19 published in journal Immunity, researchers Haley E. Randolph and Luis B. Barreiro explain the basic concepts of herd immunity and discuss its implications in the context of COVID-19. The study authors write:

“Acquired immunity is established at the level of the individual, either through natural infection with a pathogen or through immunization with a vaccine. Herd immunity stems from the effects of individual immunity scaled to the level of the population. It refers to the indirect protection from infection conferred to susceptible individuals when a sufficiently large proportion of immune individuals exist in a population. This population-level effect is often considered in the context of vaccination programs, which aim to establish herd immunity so that those who cannot be vaccinated, including the very young and immunocompromised, are still protected against disease. Depending on the prevalence of existing immunity to a pathogen in a population, the introduction of an infected individual will lead to different outcomes (Figure 1 ).”

Herd Immunity SIR (susceptible, infectious, recovered) model for a completely immunizing infection. (source: NCBI Resources)

Approaches to COVID-19 Immunity

The study authors suggests the following two methods to build widespread immunity to covid-19:

  • “a mass vaccination campaign, which requires the development of an effective and safe vaccine, or”
  • “natural immunization of global populations with the virus over time.”

In the absence of a vaccination program, establishing herd immunity should not be the ultimate goal. Instead, an emphasis should be placed on policies that protect the most vulnerable groups in the hopes that herd immunity will eventually be achieved as a byproduct of such measures, although not the primary objective itself.

Haley E. Randolph and Luis B. Barreiro in Immunity
Coronavirus Pandemic Watch

According to the MDH latest tally (as of July 27, 11 a.m.) the confirmed COVID-19 cases in Minnesota are 51,803 (out of 970,726 tested) with 1,576 deaths. According to Johns Hopkins database (as of July 27, 2:35 p.m.) there are 4,271,095 confirmed covid19 infection with 147,253 deaths. Globally the covid19 virus has infected 16,340,152 with 650,157 deaths.