COVID: Why experts say herd immunity is still out of reach

Berlin: Despite vaccination, cases of coronavirus continue to increase worldwide, from the United Kingdom, India, Russia to Malaysia. Now that German experts are talking about the imminent fourth wave, many want to know only once. When will this end?

Since the beginning of the pandemic, the term “herd immunity” has been used by enough people to immunize against the coronavirus, hug them again, release overburdened healthcare workers, and say goodbye to COVID-19. It has come to symbolize the points that can be told. ..

But what exactly is this vague Holy Grail, and why does it seem to be forever out of reach?

Herd immunity: explanation

Adam Kleczkowski, a professor of mathematics at the University of Strathclyde in Scotland, likens “herd immunity” to a wildfire that depletes dry trees. When the amount of fire is exhausted, the fire runs out of fuel and goes out. If enough people are resistant to the coronavirus by infection or vaccination, the virus cannot spread and the pandemic stops growing and begins to decline.

The percentage of the immune population required to achieve this level of community tolerance is based on reproductive (R) numbers. This is the average number of infected people who pass the disease at a particular point in time. If the R number is less than 1, that is, if one infected person is unlikely to infect multiple people, the disease begins to run out of fuel and is fatal.

“This can be achieved by waiting long enough for most people in society to become infected, socially distant and forever blocked, or by vaccination of enough people,” Kleczkowski said. “The important thing to understand is that not everyone needs to be immune. A sufficient number of people are immune and the fire no longer spreads,” he told DW. There is, “he said.

So what are the important “points” of the coronavirus?

At the beginning of the pandemic, scientists estimated this figure to be around 60-70%. But over the last year and a half, that goal post has changed. Recently, experts say that percentage is close to 80% or 90%. There are several reasons for this.

Variants cause problems

One of the problems is that this important number depends on the infectivity of the virus, the rate of spread. For highly contagious measles, this percentage is 95%, but for influenza, it can drop to 35%.

At the onset of the outbreak, the R number of coronavirus was estimated to be between 2.5 and 3.

The first confirmed Delta subspecies in India is about 64% more infectious than the first confirmed Alpha (Kent) subspecies in the United Kingdom and already 50% more infectious than the original coronavirus subspecies spread from China. The infectivity was strong.

The faster the virus spreads, the more immunity is needed to reduce the infection rate. “It shifts this number up. Slowing down the Delta variant can require as much as 85% immunity,” said Kleczkowski.

But he points out that such percentages are only estimates. “They are based on limited data. It’s not entirely clear what percentage you need to reach,” he said.

Vaccination important for herd immunity

Vaccination is the key to achieving herd immunity, said Kaja Abbas, an assistant professor of disease modeling at the London School of Economics and Tropical Medicine.

“Herd immunity by vaccination is the preferred route,” he told DW. “Herd immunity from natural infections will cost a great deal of human life and suffering,” he said.

According to a recent study conducted in Israel, the vaccine has not only prevented the vaccinated individuals from becoming seriously ill, but has also succeeded in significantly reducing the transmission of the virus.

“To get that level of immunity, a significant portion of the population needs to be vaccinated,” Abbas said, which ensures that the vaccine is evenly distributed around the world. It also means: “We are not safe until everyone is safe everywhere.”

In the United Kingdom and the United States, 50% of the population is close to full vaccination, in Israel it is close to 60%, in India over 3% and in Brazil 11% of the population are both vaccinated. People died of COVID.

In addition, you may need to re-vaccine a third or fourth dose to protect yourself from new virus variants.

New normality

Mathematical herd immunity calculations also cannot take into account the complexity of human behavior. Once a certain level of immunity is achieved, control measures such as wearing masks, physical distances, and border closures are relaxed, resulting in new outbreaks and the loss of herd immunity.

For these reasons, defining herd immunity with concrete numbers is “useless,” says Kleczkowski.

Kleczkowski says it is more useful to think of herd immunity as the process of eradicating and ultimately eliminating the virus, rather than focusing on whether herd immunity has reached 70% or 80%.

That doesn’t mean you need to allow the virus to spread to the community. Alternatively, he adds, he is in a strict, endless blockade. Instead, he recommends maintaining a combination of control measures such as ongoing testing and wearing a mask in areas of high infection.

Even if the world cannot completely eradicate the coronavirus, experts such as Abbas and Krechikovsky have said that if the infection continues to occur, the vaccine will almost remove people from the worst effects of COVID-19. It says it will protect.