Herd Immunity and COVID-19

After more than a year of living with monstrous pandemic COVID-19, the United States is beginning to see a hope. More than 3 million shots are administered every day. With over 86.3 million people fully vaccinated — more than 26% of the population — the nation is steadily moving towards building its immunity to COVID-19.

Today, herd immunity is commonly mentioned as the ultimate goal of vaccination drive, but what exactly does it mean, and when will it be attained in the United States?

What Is Herd Immunity?

When enough people have immunity to a contagious disease — whether through previous infection or vaccination — it becomes difficult for the disease to continue spreading. This provides an indirect protection throughout a group (herd), even for the people without immunity at individual level.

Source: MDPI

As per the health experts an estimated minimum percentage of a population that needs to be immune is called herd immunity threshold. The more infectious the disease, higher the threshold.

For example, a person suffering can infect 12 to 18 unvaccinated people and for such contagiousness about 95 percent of the population must attain immunity to prevent the disease from spreading. But even when the population as a whole has herd immunity, local outbreaks are still possible.

What Is the Threshold for COVID-19?

Experts have estimated that 70 to 90 percent of the population needs to be vaccinated to stop COVID-19 from spreading however there is still much to learn about this novel virus.

So far, the three approved vaccines in the United States have been effective against more transmissible and deadly variants of COVID-19, though slightly less than against the original virus.

However, if a new strain dodges the body’s immune response, that will nullify the nation’s efforts of achieving herd immunity.

Does Herd Immunity Mean a Return to Normal?

Although vaccinations are meant to contain the virus, “immunity is only one part of the equation. It’s not like an on-off switch,” the experts said. 

The virus is likely to circulate even after attaining the herd immunity threshold. It’s like taking your foot off the gas of a moving car: The car will eventually stop but at first it will cover some distance. So, those with COVID-19 will still infect others, and more infections are bound to occur downstream. 

For example, in a scenario where herd immunity is achieved and on average one infected individual spreads it to 0.8 other people. If 100,000 people have the virus, this number would be 80,000 or more. Those 80,000 will transmit the disease to 64,000 more people, and so on.