Why Fast-Spreading Omicron Won't End COVID Pandemic With Herd Immunity

COVID-19 case numbers in the U.S. appear to be decreasing, according to Centers for Disease Control and Prevention (CDC) data, as scientists continue to discuss the possibility of the virus finally becoming endemic.

The seven-day moving average of new cases has decreased since January 13, CDC data shows, with that figure at just over 700,000 on January 17, down from around 800,000 just a few days prior—though many more hospitalizations and deaths are still expected.

Meanwhile, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), said on Monday this week that it's too early to predict whether or not the Omicron variant would help push the pandemic into a more manageable endemic phase, but he "would hope that that's the case."

An endemic disease is one that is limited within certain regions or between certain populations, and its spread can become more predictable. Influenza, for example, tends to be an endemic virus.

But what of herd immunity—a situation in which enough people become immune to a virus so as to prevent it from reaching new hosts?

Herd immunity has in the past been optimistically proposed as a pandemic-ending method, though it was also often dismissed. Now, multiple scientists have told Newsweek that herd immunity is not going to eradicate COVID-19, and the virus will be with us indefinitely in some way or another.

Will Omicron Cause Herd Immunity?

There are many reasons why herd immunity against COVID-19 is unlikely. One is that the virus evolves variants very quickly, which can weaken immunity build-up as the world has already seen with Omicron, said Erin Mordecai, associate professor of biology at Stanford University.

Another is that antibody immunity against COVID-19 reduces substantially within a few months, "so even though other components of our immune systems like T-cells still provide strong protection against severe disease, our bodies are less quick to fight off infection immediately," Mordecai told Newsweek.

This point was echoed by Caroline Wagner, assistant professor of bioengineering and expert in infectious disease dynamics at McGill University, and Chadi Saad-Roy, an ecology and evolutionary biology PhD student at Princeton University.

They told Newsweek in a joint email: "It appears that immunity against infection with SARS-CoV-2 wanes over time, through a combination of decreasing in-host immunity and antigenic evolution.

"So, it does seem that the idea of achieving a level of immunity where SARS-CoV-2 will no longer circulate is unlikely."

This is in addition to the refusal by some people to get vaccinated and the unequal vaccine distribution around the world, meaning large pockets of the world have less protection than others, giving opportunity for more mutations to arise.

"I don't think it'll be as simple as: we get to a herd immunity threshold and SARS-CoV-2 transmission stops completely," Mordecai said.

It's true that humanity has proven itself capable of eradicating a disease before, with smallpox being the main example. This was made possible through an extensive global vaccination effort.

But there are key differences between SARS-CoV-2 and smallpox that makes the former harder to eliminate, according to Mordecai—it is infectious before people show symptoms; it increases in transmissibility quickly; and it can infect animals, leading to the possibility of a spillover from animals back to humans even if humans were able to prevent transmission.

Will Omicron Make COVID Endemic?

Living with COVID-19 as a permanent virus that circulates and causes mild disease is certainly a possible—but not a definite—outcome, experts said.

"I do think we're likely to see a transition over the next few years to an endemic state where the virus regularly circulates and causes mild disease, but causes fewer cases of severe disease because most vulnerable people, especially older people, have been repeatedly exposed or vaccinated and younger people are exposed earlier in life when the chances of severe disease are much lower," said Mordecai.

However, they added that the world is not yet at that state, and preventative measures like masks, testing, isolation and vaccinations are still needed to keep the virus under control.

"An endemic state may well look like more predictable outbreak timing, for example in the winter for certain regions, and one with much less associated morbidity and mortality," said Wagner and Saad-Roy.

When Might an Endemic State Be Reached?

The time frame for this is uncertain, and it's also unclear whether Omicron will be the variant that leads to an endemic state.

Mordecai thinks COVID-19 becoming endemic is "unlikely to occur in the next few months, but it is likely in the next year or two." Other experts did not propose a time frame.

"It's far too early to say whether Omicron brings us closer to the end of the pandemic," David Robertson, head of viral genomics and bioinformatics, University of Glasgow Centre for Virus Research, told Newsweek at the end of December.

"It's certainly the case that Omicron is appearing to be less harmful at an individual level but how this will play out on a population scale is worrying.

"Importantly there's nothing inevitable about a virus becoming milder—for example a SARS-CoV-2 variant that's as or more transmissible than Omicron could emerge with different properties."

According to Wagner and Saad-Roy, it will depend on how quickly the world can be vaccinated to change viral replication patterns and the emergence of new variants.