Those Who Believe in Herd Immunity Cannot Do the Math

Current data are placing the final nails in the coffin of herd immunity. The first study which prompted hopes that wide-scale herd immunity may have been obtained was published on September 2, 2021. The study analyzed 1,443,519 blood donation samples between July 2020 and May 2021. In May 2021, 83.3% of the individuals had antibodies to SARS-CoV-2. However, blood donors may be composed of health-conscious individuals who are more likely to be vaccinated. In the article, 20.2% of the specimens had infection-induced antibodies. This means that 63.1% of the individuals had antibodies from vaccination. As of May 15, 2021, 49.7% of the United States population had received at least one dose of a SARS-CoV-2 vaccine.

Thus, in the study’s population, 20.2% of the patients who donated blood in May 2021 had had an infection. Of those donating blood, a total of 63.1% were vaccinated, but one would expect just 49.7%. By adding 49.7% and 20.2%, one can estimate that 69.9% of the population had at least some immunity to SARS-CoV-2 in May of 2021.

Source: Our World in Data. Accessed January 26, 2022. https://ourworldindata.org/covid-vaccinations?country=USA https://github.com/owid/covid-19-data/blob/master/public/data/vaccinations/vaccinations.csv

Recently another study was published in JAMA Network which found that 72% of residents in Los Angeles County had protective immunity to SARS-CoV-2 in April 2021. On viewing this data, many felt that a degree of herd immunity had been reached and if outbreaks were to occur, they would be regionalized and confined to areas with lower vaccination rates.

However, this did not happen. The United States endured another large surge from the Delta and Omicron variants.

The Delta variant is about 50% more transmissible than the wild type of virus and the Omicron variant has been found to be 2.7 to 3.7 times more infections than the Delta variant. Both variants have infected a large number of individuals.

Source: Worldometers. Jan 26, 2022. http://worldometers.info

Source: Worldometers. Jan 26, 2022. http://worldometers.info

Since the May 15, 2021 survey of SARS-CoV-2 seropositivity in the United States, we have had more than double (2.17 times) the number of cases of SARS-CoV-2. Of course, some of these may well be reinfections and breakthrough infections. The United Kingdom is reporting that with Omicron cases, at least 9.5% these are reinfections. The Omicron peak so far comprises about 22 million cases (December 15 to January 25) in the United States, so it can be assumed that reinfections and breakthrough infections will produce some decrease in the estimates of the total number of unique cases.

Kevin Kavanagh, MD

If we now assume an infection rate of 2.0 times, then 40% of our population has been infected with SARS-CoV-2. (Double the May 15, 2021, estimate of 20%). We may well have over 90% of the United States population with some immunity. But we are still at the height of a severe surge, with a new variant, the stealth Omicron, looming; and this variant’s infectious potential appears to be even greater, as it is outcompeting Omicron. It is unclear if this potential is due to an ability of the stealth Omicron to escape immunity or if the variant is finding the last remnants of immune-naive individuals.

As the pandemic continues to progress, reinfections and outbreak infections are causing the ‘vaccinate and all will be well’ advocates and the ‘herd immunity’ advocates to change their narratives.

The original goal of both groups was to prevent disease and end the pandemic. In the summer of 2020, a goal for vaccine approval was to “prevent disease or decrease its severity in at least 50% of people who are vaccinated.” However, the prevention of disease has been emphasized, with the initial Phase III trial for Moderna having its primary end point as “the efficacy of the mRNA-1273 vaccine in preventing a first occurrence of symptomatic COVID-19” and Pfizer announcing its vaccine prevented 100% of symptomatic cases in adolescents age 12 to 15.

According to the United Kingdom’s Imperial College COVID-19 response team, a two-dose vaccine (AstraZeneca and Pfizer) provides a vaccine effectiveness in the prevention of symptomatic disease between 0% and 20% with the Omicron Variant, and a previous infection gave a protection of 19%. However, unlike infections, you can safely receive a booster with an mRNA vaccine. Three-dose vaccinations provide a vaccine effectiveness for the prevention of symptomatic disease from Omicron of between 55% and 80%.

Now both advocacy groups are stating the primary goal for vaccines and herd immunity is the prevention of severe disease, as defined by hospitalizations and deaths.

Preventing hospitalizations and deaths in those who are infected is an important goal. Although hospitalizations are surging from the Omicron variant, the system no longer has redundancy in staffing and large number of workers are becoming infected and off of work because of COVID-19 infections. Thus, even outpatient infections which occur en masse can cause great disruptions in critical services, resulting in patients with non-COVID illnesses having difficulty obtaining treatment. Even patients with true emergencies may be waiting hours, which can greatly affect treatment and survival for those with cardiovascular diseases.

COVID-19 mutations are evading our immunity and at the same time our immunity is waning.Herd immunity to disease and the eradication of SARS-CoV-2 is no longer possible.SARS-CoV-2 is becoming endemic. Endemic means we have lost the fight to eradicate this virus.Whether we live or die with SARS-CoV-2 now depends upon how rigorously we adopt and implement public health mitigation strategies.