What is herd immunity?

As the number of COVID-19 cases continues to increase worldwide, scientists around the world are working hard to find the best way to protect everyone from COVID-19 infection. Herd immunity is one possible way to control the spread of COVID-19.

The following knowledge about herd immunity can help us understand how herd immunity will slow the spread of the new coronavirus.

Herd immunity, or community immunity, is when a large portion of a population is immune to a disease. If enough people are resistant to a virus or bacteria, it can't spread.

Although not every individual is immune, the herd as a whole is immune because there are fewer people at risk overall. As the infection rate decreases, the disease gradually dies out.

Herd immunity protects high-risk groups, including infants and those with weakened immune systems who cannot develop resistance to pathogens on their own.

How to achieve herd immunity? There are two ways to achieve herd immunity.

1. Resistance develops after natural infection. When an individual is exposed to a virus or bacteria, they produce antibodies to fight the infection. When the individual recovers, they retain those antibodies. The individual is protected against the next infection. This is how the Zika outbreak was stopped in Brazil. Two years after the outbreak, 63% of the population had been exposed to the virus. Researchers believe the region has fully reached herd immunity.

2. Through vaccination. Vaccines also create resistance. Vaccines cause the body's immune system to think the recipient is infected with a virus or bacteria and initiate the synthesis and secretion of antibodies. Although the recipient is not sick at this time, the immune system still produces protective antibodies. The next time the recipient's body encounters the previous bacteria or virus, it is ready to fight it. This is how polio was eliminated in the United States.

When does a population reach herd immunity?

This depends on the basic reproduction number, or R0. R0 refers to the average number of people that a virus carrier can infect. The higher the R0, the more people need to be resistant to achieve herd immunity.

Researchers believe that the R0 for COVID-19 is between 2 and 3, meaning that one infected person can infect two to three others. This also means that between 50% and 67% of the population would need to be resistant before herd immunity kicks in and infection rates start to drop.

What are the challenges in achieving herd immunity against COVID-19?

The main obstacle to herd immunity against COVID-19 right now is that the virus that causes the disease is new. This means it has not infected humans before, no one has immunity to fight it before, and everyone is at risk of being infected.

Without COVID-19 vaccination, a large number of people will need to be infected and sick, and enough patients will need to recover to achieve herd immunity. And those infected with low immunity will pay the price with their lives. This is the biggest challenge facing humanity.

Currently, many countries are gradually carrying out large-scale vaccination of the new crown vaccine. According to the latest reports, the global vaccination volume has exceeded 100 million doses, which has exceeded the total number of confirmed cases of the new crown. The cumulative number of vaccinations in my country has also exceeded 30 million doses. Large-scale vaccination is the only correct way for humans to achieve herd immunity against the new crown.