If you’re still waiting for herd immunity for COVID-19, it’s time to move on: Experts


If you're still waiting for herd immunity for COVID-19, it's time to move on: Experts

At the beginning of the pandemic, scientists and public health experts drew on their experience with other viruses to make predictions about COVID-19, hoping that if enough people developed immunity, the virus would be stopped.

But in the years that followed, and even after the introduction of highly effective vaccines, vaccine scientists and public health experts interviewed by ABC News noted that COVID-19 is unlikely to go away entirely.

Although herd immunity through widespread vaccination can be a successful strategy for certain viruses, such as B. those that cause smallpox and polio, scientists no longer consider them an appropriate management strategy for the virus that causes COVID-19, these experts said.

Herd immunity refers to a situation in which a virus cannot spread because it repeatedly encounters people who are resistant to it. As a result, a small number of people who lack resistance can still be protected from the “herd” of resistant people around them, as they are less likely to spread the virus to them.

But herd immunity depends on some hidden assumptions. First, that resistant people remain resistant. Second, that resistant (or vaccinated) people cannot transmit the virus. Scientists have learned over the past two years that these assumptions do not apply to COVID-19.

PHOTO: A registered nurse administers a dose of COVID-19 vaccine to an 85-year-old woman at a state immunization center at the Allen Senior Citizens Housing Complex in Queens, New York, on February 20, 2021.

A registered nurse administers a dose of COVID-19 vaccine to an 85-year-old woman at a state immunization center at the Allen Senior Citizens Housing Complex in Queens, New York, February 20, 2021.

Anthony Behar/Sipa USA via AP, FILE

Vaccination scientists and public health experts said herd immunity for COVID-19 is not realistic based on what we have learned about the virus itself.

Most importantly, immunity wears off relatively quickly, and vaccinated individuals can still transmit the virus, especially when confronted with rapidly evolving new variants. Meanwhile, human behavior has been hard to predict as vaccine rollouts have been slower than hoped and constant changes in social distancing are affecting scientists’ ability to predict and prepare for the future.

Insights into the virus itself

Rarely does a vaccine offer total and complete protection against infection. On the one hand, tetanus shots can last for over 30 years. But with COVID-19, both infection- and vaccine-induced immunity wanes over time.

“When you get a vaccine, it triggers two types of immune responses,” said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, told ABC News. “One answer is to produce antibodies that last three to six months. Antibodies can even protect against mild diseases.”

Antibodies are proteins that bind to viral particles to inactivate them. They also help prevent people from spreading the active virus to others because they can bind the virus before it gets to anyone else.

Antibody-based immunity to mild illness wears off after three to six months. However, immunity against severe disease is maintained due to the second immune response.

PHOTO: Pedestrians in Times Square in New York, May 22, 2022.

Pedestrians in Times Square in New York, May 22, 2022.

Bloomberg via Getty Images

“The second response is to make memory B and T cells, which are more long-lived,” Offit said.

Memory cells tend to remain dormant and need a trigger before they start making antibodies.

The virus that causes COVID-19 has a short incubation period. Most infected people become contagious within the first few days, well before memory cells are activated to make antibodies.

Because memory cells eventually work after about two weeks, infections usually don’t progress beyond mild illness. But by then, many people will have spread the virus to others.

“All vaccines still offer robust protection against serious diseases,” said Dr. Dan Barouch, a virologist and immunologist at Harvard Medical School, told ABC News. “None of the vaccines do a very good job of preventing infection.”

insights into human behavior

Less than 70% of Americans are fully vaccinated two years after vaccines become available. Many countries around the world have even worse vaccination coverage.

Leaving reservoirs of unvaccinated people is like leaving combustible material around a forest fire. With plenty of fuel to feed it, the fire keeps burning. Each new infection is a chance for the virus to grow and mutate. Some mutations could confer resistance to vaccines.

“Currently, the vaccine and boosters are free […] and accessible through public mass vaccination sites,” Azra Behlim, PharmD, MBA, Associate Vice President of Pharmacy Sourcing & Program Services at Vicient, a healthcare services company, to ABC News.

In the future, things could shift towards a fee, like other vaccines.

“[Federal] decisions […] whether or not the provisions of the COVID Relief Act are extended will impact whether this postponement occurs now or at a later date,” Behlim said.

Experts speculate that if vaccines were received every three to six months so that antibodies never waned, true herd immunity could occur. But the logistics of launching vaccines and concerns about booster fatigue make that impossible.

“The only reasonable goal of this vaccine is to prevent serious disease,” Offit said, noting the significantly lower death and hospitalization rates now that more Americans are vaccinated.

As experts shift from herd immunity to preventing serious diseases, social distancing measures need to be established at the local level, they say.

But social distancing guidelines use assumptions about human behavior, not just virus behavior, experts said.

“We have a snapshot of what happened over time, but as people’s behavior changes, those assumptions become less valid and the models tend to erode,” said Dr. John Brownstein, ABC News contributor and chief innovation officer at Boston Children’s Hospital.

As more virulent and contagious variants emerge, epidemiological models must change rapidly.

Genevieve Yang, MD, Ph.D., is a New York City psychiatrist and a fellow at the ABC News Medical Unit.

You May Also Like