How long do vaccines protect against coronavirus?

Exclusive tour inside the Pfizer vaccine factory 3:50

(CNN) – Ian Haydon helped test Moderna’s coronavirus vaccine last year. Now he is helping to test the modified version of that vaccine designed to combat a new and more contagious variant.

“A year ago I tested the Moderna vaccine to see if it was safe. (Spoiler: It is!) Now on my #COVIDvaccine anniversary, I’m happy to share that I just got a third dose. This booster experiment will reveal (1) whether the strain-tailored vaccines increase immunity and (2) whether they are safe, ”Haydon, a communications specialist at the University of Washington, said via Twitter on Saturday.

“It is not clear if this new modified version will be necessary,” Haydon told CNN in a telephone interview.

“But it is being developed and tested right now so that we have it on hand.”

Doctors are concerned that the coronavirus could end up being like influenza, requiring a new vaccine every year, both because circulating strains mutate quickly and because the vaccine’s immunity wears off quickly.

Although initial evidence suggests that immunity from coronavirus vaccination provides long-lasting protection, vaccine manufacturers have begun manufacturing and testing versions of their vaccines that protect against worrisome variants of the virus. That includes version B.1.351 first identified in South Africa, which carries a mutation that, in laboratory experiments, appears to allow it to slightly evade the human immune response.

The latest report from vaccine maker Pfizer shows that people in South Africa who received their coronavirus vaccine after B.1.351 became the dominant circulating virus were still heavily protected from infection, something that supports laboratory experiments. They have shown that the vaccine causes such a strong response that it provides a cushion against the effects of virus mutations.

“It’s still close enough that we have good protection,” said Scott Hensley, an immunologist and vaccine expert at the University of Pennsylvania.

But vaccine manufacturers are taking no chances. The trial in which Haydon participates tests not only a third dose of Moderna’s vaccine adjusted to specifically protect against B.1.351 – that’s what he got – but also a third dose of the original vaccine in some volunteers, to see if the enhanced immune response is safe and offers an advantage.

A report published last month by Pfizer suggests that people who receive both doses maintain strong immunity for at least six months. Experts have taken pains to point out that this does not mean that immunity stops after six months. It means that the trial volunteers have been followed longer to see what their immunity is. It’s likely to last much longer, according to Hensley.

“I wouldn’t be surprised if we learned a year from now that these vaccines still produce a strong immune response,” Hensley told CNN.

“I wouldn’t be surprised if this is a vaccine that we only get once.”

That would make the vaccine look more like measles vaccines than flu vaccines. Measles vaccination protects against lifetime infection in 96% of people.

Protection from Pfizer’s two-dose vaccine remains above 91% even at six months, according to the company. It has released the details in a statement, not a formal scientific publication, and the data covers only a few thousand people. But if it holds up, it’s an indication that both the Pfizer and Moderna vaccines elicit a long-lasting immune response, experts say.

Hensley explains that the technology used by both vaccines, the delivery of genetic material known as messenger RNA from mRNA, is especially powerful.

‘The antibody responses elicited by these mRNA vaccines are incredibly high. What we know in animal models with other mRNA vaccines that have been tested before is that these antibody responses are incredibly long-lasting and don’t diminish over time, ”said Hensley, whose lab has tested experimental mRNA vaccines for years.

While coronavirus vaccines are, of course, new (the virus has only been around since late 2019), mRNA technology has been studied for several years and has been used to make vaccines against influenza, Ebola, and the virus. of Zika.

Several studies have indicated this with the coronavirus vaccine.

In January, a team led by Dr. Alicia Widge at the National Institute of Allergy and Infectious Diseases wrote in the New England Journal of Medicine that their research showed that two doses of Moderna’s vaccine produced many antibodies that decreased very slightly with the weather. The vaccine also caused the body to produce immune cells known as T cells and B cells, which can keep defenses active for years. They found that the immune response induced by the vaccine was stronger and less variable than the immune response that follows a natural infection.

Pfizer confirms the protection time of its vaccine 1:01

Another study in the New England Journal of Medicine in February revealed that blood drawn from people who received the Pfizer / BioNTech covid-19 vaccine continued to produce an immune response against the B.1.351 variant.

“Although we do not yet know exactly what level of neutralization is required for protection against COVID-19 disease or infection, our experience with other vaccines tells us that the Pfizer vaccine is likely to offer relatively good protection against this new variant,” Scott Weaver, director of the Human Immunity and Infections Institute at the University of Texas Medical Branch, told CNN at the time.

However, last month, South African virologists argued that there is mounting evidence that the vaccines being developed do not work as well against B.1.351 and urged vaccine manufacturers to start adjusting their formulas.

And even though Haydon participates in clinical trials that require regular blood draws to test his immunity, he has no idea how well he is protected against the virus.

“I know that at the beginning of the trial, all the participants and I developed neutralizing antibodies, the kind you are looking for. That was clear many, many months ago, ”Haydon said. “But the level of those antibodies, and how the levels have changed over time, is not something they tell me. That is one of the main things that will be evaluated during the study.

He had a strong reaction to the first round of vaccination and said that the third dose he had just received caused some effects as well.

“Like a cold, it’s the correct way to describe my symptoms,” he said. “I ended up with a fever, chills, a little nausea, a headache,” he added.

Immunologists say it is a sign that the immune system is responding to the vaccine, although people who do not report symptoms also develop an immune response, so the symptoms do not seem to suggest that someone has a better response than someone who does not have a fever. .

Haydon doesn’t know if his answer this time says anything about the level of immunity he still had from the first dose he gave a year ago.

What you do know is that you cannot behave as if you are completely immune. So he still wears a mask every time he goes out and has avoided almost every trip.

“We live in a world where most people are not vaccinated. Just because you’re vaccinated doesn’t change everything for you, ”Haydon said.

“We still have to take many of the same precautions as an unvaccinated person.” Although the risk of going to the hospital is greatly reduced, the spread of the virus is a major concern. It’s not until recently that we started collecting data (showing) that vaccinated people also transmit much less of the virus. This is a recent discovery and a very good sign.