Herd immunity. That has been the longed-for goal since the COVID pandemic began. Once we reach herd immunity, we’ll rein in the coronavirus and life can get back to normal.

Now, almost half a year into the vaccination rollout, health experts are questioning whether the United States can actually reach herd immunity.

Herd immunity is the idea that if you get enough people vaccinated, the virus will have nowhere to go. When you reduce the number of potential hosts, the virus has a harder time jumping person to person. And eventually, the virus dies out or becomes isolated and easily containable.

So why do experts now think herd immunity is unlikely? Because of rapidly evolving COVID variants and vaccine hesitancy.

The vaccination campaign is a race against the COVID variants. You want to get as many people vaccinated before the virus evolves to a point where the vaccinations lose their effectiveness.

Even though half of Americans have received at least one dose, demand for vaccines has dropped recently. Most of those eager to get vaccinated have already done so. That leaves people who are hesitant to get the vaccine and those who are harder to reach through traditional vaccine outlets.

This may lead some to think: Why bother getting vaccinated at all?

Because vaccinations are crucial to limiting the spread of COVID. With enough vaccinations, the pandemic could transform into a manageable threat. COVID would continue to circulate but with far fewer hospitalizations and deaths.