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How Long Do Covid-19 Vaccines Provide Immunity?

logo de La Nouvelle Tribune La Nouvelle Tribune 13/04/2021 WSJ

Pfizer, Moderna and Johnson & Johnson vaccines provide good protection against the virus that causes Covid. But how long does that last? Will you need a booster shot? Here’s what we know.

By Sumathi Reddy – The Wall Street Journal.

How long does protection from Covid vaccines last? It’s a question that’s becoming more important as some of the first people to be vaccinated approach four months post-inoculation.

The short answer is: We don’t fully know yet. But more data is coming in that provides clues. Here’s what we know so far.

How long are we protected from getting Covid-19? Does the efficacy decline over time?

Recent data from Pfizer, the manufacturer of one of the three vaccines available in the U.S., indicates that protection lasts at least six months. The results showed minimal antibody decline. Recipients of the Moderna vaccine also had robust levels of antibodies more than six months later, according to a recent study published in NEJM.

Some people have incorrectly concluded that means that those vaccines offer only six months of protection, says Scott Hensley, a professor of microbiology at the University of Pennsylvania. “That’s false,” says Dr. Hensley. “We only have six months of data…Six months from now it’s likely we’ll learn we have one year of protection.”

How does protection provided by these vaccines work?

The vaccines will likely provide at least some degree of protection for a long time because there are so many layers of immunity, says Deepta Bhattacharya, an associate professor of immunobiology at the University of Arizona in Tucson.

The first shots of the two-shot Pfizer and Moderna vaccines provide reasonable protection. Then the second shot bumps up the level of antibodies and T cells produced by the body, he says. T cells are white blood cells that destroy cells infected by viruses. There’s “a lot of room to decline and still be protected,” he says.

Will the protection provided by the Johnson & Johnson vaccine last as long as Pfizer and Moderna’s?

Johnson & Johnson uses a different platform for its vaccine, and hasn’t been around long enough to have data out as far.

The level of antibodies in people who receive the Johnson & Johnson vaccine appears to keep increasing between two weeks and 70 days post-vaccination. So even though J&J’s reported efficacy is lower than Pfizer and Moderna’s, Dr. Bhattacharya says it may be similar at a later point in time.

Could the vaccines provide lifelong immunity?

It’s possible some level of protection could last for years or even decades, some scientists say, but we don’t know.

A 2020 Nature study found that patients who got SARS—a similar coronavirus to the one that causes Covid-19—still had T cell immunity 17 years later, says Monica Gandhi, an infectious disease physician and professor of medicine at the University of California, San Francisco.

Dr. Gandhi notes that even if antibody levels wane, there is evidence from a new preprint that memory B cells are generated by the Pfizer vaccine seven weeks after vaccination. Memory B cells are white blood cells that can be stimulated to produce new antibodies decades later. A 2008 Nature study found that survivors of the 1918 influenza pandemic were able to produce antibodies from memory B cells when exposed to the same influenza strain nine decades later.

Will emerging variants affect how long protection from vaccines lasts?

It’s hard to predict.

So far, the vaccines appear to provide good protection against most of the known variants. But as the virus continues to mutate, more problematic variants may emerge that are better able to skirt vaccine-induced defenses. Such variants might already exist but just haven’t been sequenced and discovered, says Dr. Bhattacharya. “If they exist already, there will be selective pressure for these variants to increase in prevalence as we get closer to herd immunity,” he notes.

This is where antibody levels become very important, says Dr. Hensley. The mRNA vaccines elicit antibody levels that are generally higher than a natural infection. Even if a variant prevents some antibodies from binding to the virus, the vaccines create so many antibodies that they should still offer some protection, says Dr. Hensley. But we don’t know how much, and for how long.

What happens if a variant makes a vaccine less effective?

The immune system is not all or nothing, notes Ann Sheehy, an immunologist and virologist at College of the Holy Cross in Worcester, Mass. It’s possible for a variant to reduce a vaccine’s protection but not entirely eliminate it.

If someone does get Covid-19 despite being vaccinated, the illness would likely be less severe. “The immune system is very clever. The second time you see something you often do better with it,” says Dr. Sheehy.

What about boosters?

Drug companies are scrambling to test booster shots for some of the new variants.

Boosters will likely be needed for at least a few years “out of an abundance of caution, knowing that immunity does wane in some individuals more than others,” says David Topham, a professor of microbiology and immunology at the University of Rochester Medical Center.

Some experts say boosters may continue to be needed for longer, particularly if the virus changes a lot.

One big difference between the coronavirus that causes Covid-19 and the other seasonal coronaviruses like the one that causes the common cold is that the Covid-19 virus can replicate anywhere in the body. The seasonal coronaviruses generally replicate only in the respiratory tract, says Dr. Topham. It’s unclear whether the Covid-19 virus may eventually become like the other common coronaviruses that cause only mild illness, or whether it will retain its ability to cause severe disease without annual booster doses.

I had no side effects from my second vaccine. My husband did. Does that mean he has more protection than me?

No. In general, scientists say side effects are a good thing. They are a signal that your immune system is at work, says Dr. Sheehy.

“Your immune system has been driven to know that you got exposed to something foreign,” says Dr. Sheehy. “If someone feels very ill they’ve generated a robust immune response.”

The converse is not true, however. “Just because you don’t feel sick does not mean you didn’t generate a robust immune response,” she says.

What about protection from a natural infection?

The Centers for Disease Control and Prevention recommend getting the Covid-19 vaccine even if you’ve already had an infection. Evidence suggests that protection via natural infection can be strong but differs by person.

A Lancet Microbe study found that the immune response was variable with some people losing antibodies within three months and others having very high levels eight months later.

“I think in reality it’s going to vary from person to person,” says Dr. Topham. “Making a good initial immune response is key.”

Featured article licensed from the Wall Street Journal.

The post How Long Do Covid-19 Vaccines Provide Immunity? appeared first on La Nouvelle Tribune.


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