Is Reaching Herd Immunity a Reality or a Dream?
With the emergence of the B.1.1.7, B.1.351, and now the P.1 (Brazilian) SARS-CoV-2 variants, will the U.S. ever reach herd immunity?
With a COVID-19-free world on the horizon, the emergence of the B.1.1.7 and B.1.351 SARS-CoV-2 variants has raised concerns from scientists about the likelihood of reaching herd immunity in the United States.
What is Herd Immunity?
Scientists use the term, Herd Immunity, to describe the act of protecting a population of individuals from a disease, by immunizing the majority of the population. This mass of immune people “protect” the few who are not immune to the disease.
Epidemiologists and statisticians calculate the “basic reproduction number,” or “R0” of a disease in order to determine the threshold - the minimum percentage of individuals that must be immune to an infectious disease for herd immunity to be reached. The value of R0 indicates the number of people in an unprotected population that one infected person can transmit the disease to. This number varies based on the rate of infection of different diseases. For example, according to the World Health Organization (WHO), the measles is “one of the world's most contagious diseases,” with a R0 range of 12-18 and a threshold of 93-95%. In comparison, the R0 of COVID-19 is estimated to be 2-4 with a rough threshold estimate of 65-70%.
The emergence of B.1.1.7 (UK) and B.1.351 (South Africa), significantly more infectious variants, has increased the R0 of COVID-19, and thus increased the threshold of herd immunity. This new development raises concerns from scientists and public health officials about the impact of the variants on the ability for the US to reach herd immunity; even with the ongoing administration of COVID-19 vaccines from Pfizer BioNTech, Moderna, and Johnson & Johnson.
Addressing the elephant in the room: will these vaccines protect us against the COVID-19 variants?
Dr. Michael Diamond, a Washington University in St. Louis Professor of Medicine and infectious disease expert, is skeptical. He states in a WUSTL news release, “We’re concerned that people whom we’d expect to have a protective level of antibodies because they have had COVID-19 or been vaccinated against it, might not be protected against the new variants.” Dr. Diamond is concerned that, “Some people, especially older and immunocompromised people, may not make such high levels of antibodies. … The concern is that the people who need protection the most are the ones least likely to have it.”
The COVID-19 variants all have a different mutation, or genetic alteration, that affects their spike protein; the protein that studs the outside of the SARS-CoV-2 virus and helps it infect cells. The problem? The current COVID-19 vaccines all use the “original” spike protein template - so will these vaccines prepare our immune systems for COVID-19 2.0?
“We don’t exactly know what the consequences of these new variants are going to be yet,” Diamond continues. “Antibodies are not the only measure of protection; other elements of the immune system may be able to compensate for increased resistance to antibodies. That’s going to be determined over time, epidemiologically, as we see what happens as these variants spread.”
Dr. Galit Alter, Professor of Medicine at Harvard Medical School, shares a more optimistic perspective in an article by The Harvard Gazette. She explains,“What we’re seeing is that these variants don’t seem to affect T-cell immunity all that much and they [the T-cells] seem to be as effective in recognizing these variants as they do the original virus.” Dr. Alter says that the current COVID-19 vaccines not only ramp up neutralizing antibody production, but they also build up T-cell protection. Even if our antibodies are ineffective against these new strains, our T-cells - our immune system’s backup troops - provide protection against the variants; how much protection remains unknown.
According to the US CDC (United States Center for Disease Control and Prevention), as of March 9, 2021, there are 3,283 reported cases of the B.1.1.7 strain, and 91 reported cases of the B.1.351 strain in the US. As vaccine rollout continues, the CDC reports that over 95.0 million doses of COVID-19 vaccines have been administered.
Dr. Alter acknowledges that the emergence of the novel variants raises the COVID-19 herd immunity threshold; however, she remains optimistic that reaching herd immunity in the US, with the help of vaccines, will be achievable.
With the continued rollout of COVID-19 vaccines worldwide and the emergence of the novel SARS-CoV-2 variants, only time will tell whether achieving herd immunity is possible. However, it appears that the majority of the COVID-19 vaccines are protecting the population from repeated breakouts. Dr. Galit Alter is hopeful, “These data give us hope that even with the vaccines that do not confer 95 percent protection against these emerging variants, the light at the end of the tunnel is approaching.”
Clear, informative, excellent writing. Keep up the good work!