Saturday , September 18 2021

Vaccine efficacy for delta: immune system explained

There has been a lot of news about New York University research suggesting that the Johnson & Johnson Covid vaccine is less effective against the delta variant because it elicits fewer antibodies. And many are wondering if people’s antibody levels will decrease and need a booster shot for several months.

Antibody levels are one piece of the puzzle when it comes to fighting Covid, but they do not tell the whole story when it comes to immunity.

Here’s what you need to know:

There is more to the immune system than antibodies

The recent NYU study, which has not yet been peer-reviewed, focuses on measurements of antibodies (in a lab environment), but that is just one of many aspects of the immune system that contribute to protection against Covid, according to Shane Crotty, professor at the La Jolla Institute of Immunology who studies how the immune system remembers infections and vaccines.

“Your immune system is complex, and does not have just one weapon,” Crotty says. “You have neutralized antibodies, other types of antibodies, you have memory B cells and T cells.”

Think of your immune system as a football team, Crotty suggests. “If you just pay attention to the wide receiver’s stats, those are useful numbers, but you miss all the things the other teammates are doing that actually affect the outcome,” he says.

(Johnson & Johnson told CNBC that their own data show that the vaccine “generated strong, sustained activity against the delta variant and other very common variants.”)

What are B and T cells?

Antibodies are important – they bind to and essentially determine the surface of the virus to prevent it from invading a cell, although it is not yet clear how long Covid antibodies will last or to what extent they will protect you, according to the Centers for Disease Control and Prevention,

But there are other important players in Covid immunity, namely B cells and T cells. These cells are special white blood cells (called lymphocytes) that work together to fight off an infection and can quickly remember how they can fight it in the future.

There are several types of B cells and T cells that work in complex ways (memory B cells, for example, are a subset of B cells that develop after an infection). But in essence, B and T cells are long-lived and can survive antibodies.

“B cells and T cells live, therefore [they] can divide and change into memory cells and other cell types that can last for many years and react when an infection is found again, “says Kaul. Antibodies produced by B cells are unable to reproduce, so levels tend to go down with time if the infection does not counteract, he says.

B cells, on the other hand, will maintain a high level of circulating antibodies for an extended period of time, Kaul says. That, just because there is no specific level of antibodies in a person’s blood, does not mean that immunity is lost.

Faxes essentially deliver B and T cells (in different ways). “This memory response is what makes second infection, third infection with the same viruses much easier [to fight], and in many cases we will not even get sick because our immune system recognizes the virus so quickly, “said Dr. Shira Weingarten-Gabbay, a scientist in the Sabeti Lab at the Broad Institute of MIT and Harvard, during a interview with the YouTube channel “Science IRL.”

Fortunately, research suggests that B and T cell levels initially rise (from one to six months after infection, B cells actually increase) and then, over time, remain constant, according to research by Crotty that was published in early 2021. Antibodies tend to shrink after an infection subsides.

Your immune system continues to learn

In addition to the various “weapons” of the immune system, its evolving nature is important.

“The immune system is a kind of plastic in the sense that it ‘stays in the classroom,'” says Dr. Dan Kaul, Professor of Infectious Diseases at the University of Michigan. In other words, the immune system always learns how they adapt to bacteria and viruses and how they react.

For example, a study by the National Institutes of Health published in March found that a type of T cell responsible for destroying cells infected with SARS-Cov-2 could recognize three Covid-19 variants: alpha, beta and gamma. (Delta was not prevalent in the US at the time.)

When you receive a vaccine, it requires your body to generate an immune response that is very specific to the particular variant that the vaccine is designed to emulate. But “over time, our immune system intentionally makes some mistakes and broadens that response type, so that over time, you may actually see better responses to variants than you do at first,” says Kaul. This can take months, he adds.

One thing that is noteworthy about the recent study of the J&J vaccine is that it was done fairly early after vaccination. Other studies on the J&J vaccine that later looked at vaccination after immune responses have seen better responses to variants, Kaul says.

Faxes are still working

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