While getting two doses of vaccine creates a strong immune response that reduces the risk of severe disease by more than 90%, the protection against milder and asymptomatic infections drops off gradually.
That’s why Pfizer has asked for and received US Food and Drug Administration authorization to add boosters for many people who are six months out from vaccination.
“I think that we expect that immunity will slowly wane, over time, but it’s not a reason for people to panic,” said Dr. Ann Falsey, a specialist in viral respiratory diseases at the University of Rochester School of Medicine.
“It’s not like suddenly one day you’re completely susceptible, like you were before you were vaccinated,” added Falsey, who is helping lead clinical trials of Covid-19 vaccines.
“The vaccines are all standing up pretty well — Pfizer, Moderna and Johnson & Johnson — for severe disease,” Falsey told CNN. “Now, that’s not to say that we might not eventually get to a point where we really need people to get boosters to prevent more severe illness. But, really, the majority of the breakthrough infections are colds, maybe flu-like illness — not the scary illnesses that we were facing before. So my main message is, don’t panic. You’re going to be okay.”
That hasn’t stopped Americans from flocking to get boosters. This past week more people were getting booster shots that were getting their first round of a coronavirus vaccine. By Friday, more than seven million Americans had received either booster shots of the third round of vaccines authorized for people with immunocompromising conditions who likely did not get adequate responses to the first two shots.
One study from Israel covered 4,800 health care workers and showed antibody levels wane rapidly after two doses of vaccine, “especially among men, among persons 65 years of age or older, and among persons with immunosuppression.”
A second study from Qatar showed protection from the Pfizer vaccine peaked in the first month after vaccination and then begins to wane.
“These findings suggest that a large proportion of the vaccinated population could lose its protection against infection in the coming months, perhaps increasing the potential for new epidemic waves,” the team wrote in a report published in the New England Journal of Medicine.
How can protection wane against mild or asymptomatic infection while staying strong against severe disease?
It’s because the human immune system is complex.
Antibodies form the first line of defense, stopping a virus from getting into some cells in the body. This is the protection that starts to wear off after time.
But there’s a second line of defense — cell-based immunity. Cells called B cells and T cells can take longer to generate than antibodies, but they provide a longer-lived, broader defense against infection and are responsible for decreases in severe infections.
So while people may be susceptible to mild illness after they’ve been vaccinated, they’re much less likely to get really sick, end up in the hospital or die.
“But there’s a lot of reasons people don’t want to get sick. They don’t want to pass it to loved ones. People don’t want to pass it to young children that can’t get vaccinated yet,” Falsey said.
The US Centers for Disease Control and Prevention has been saying for months that’s why even fully vaccinated people need to continue taking precautions against infection — wearing masks when around a lot of other people who may or may not be vaccinated, especially indoors, and making sure rooms are well ventilated.
“They just don’t need to storm the pharmacies and panic.”
The people getting boosters now should have been among the first to have been vaccinated — in January, February and March. They include people 65 and older, adults with conditions putting them at risk of severe disease and people in occupations or living conditions that put them at higher than average risk of infection.
Everyone else should cool it for now.
“They just don’t need to storm the pharmacies and panic,” Falsey said.
People should not go ahead and get booster doses if it hasn’t been six months since their last dose of Pfizer vaccine, because they will not get the best immune response, Fauci said in a White House briefing last month.
“There will be temptations, for example, for people who recently got vaccinated to not wait for the six month period of time,” Fauci said. But waiting for several months after the initial immunization to boost helps produce a stronger response. Immune system cells that help restore waning immunity respond more robustly if they are allowed to go into a resting state after the first round of vaccination.
That said, most people should eventually plan on getting boosters, Falsey said.
“Probably it’s going to be true of any of the vaccines, not just Pfizer — we’ll benefit from boosting immunity. That’s not the same thing as saying it’s critically necessary,” she said.
While people who have recovered from an infection have some protection, they’re even more protected if they get vaccinated, too.
“I think that, depending on your own natural immunity because you feel like you’re a strong person is like playing Russian roulette,” Falsey said.
Even young, seemingly healthy people have become seriously ill from Covid-19 and have died from it.
“I would never depend only on my natural immunity to weather this virus. It’s a very, very bad actor,” Falsey said.