Although two doses of vaccine create a strong immune response that reduces the risk of serious illness by more than 90%, protection against mild and asymptomatic infections gradually decreases.
Therefore, Pfizer has requested and received permission from the U.S. Food and Drug Administration to add boosters to many people who are six months from vaccination.
“I think we expect immunity to slowly decline over time, but that’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 you ‘one day are suddenly as susceptible as you were before you were vaccinated,'” added Falsey, who helps lead clinical trials on Covid-19 vaccines.
“The vaccines are all doing pretty well – Pfizer, Moderna and Johnson & Johnson – for serious illness,” Falsey told CNN. “Now that’s not to say that we may not eventually get to a point where we really need people to get boosters to prevent more serious illness. But really, the majority of the breakthrough infections are colds, maybe flu-like illness- not the scary diseases we faced before. So my main message is, do not panic. You’ll be okay. “
That has not stopped Americans from flocking to get boosters. In the past week, several people got booster shots that got their first round of a coronavirus vaccine. By Friday, more than seven million Americans had received either booster shots of the third-round vaccine approved for people with immune-compromising conditions, who probably did not get adequate responses to the first two shots.
A study by Israel covered 4,800 healthcare professionals and showed that antibody levels decreased rapidly after two doses of vaccine, “especially among men, among people 65 years or older and among people with immunosuppression.”
Another study from Qatar showed that protection against the Pfizer vaccine peaked in the first month after vaccination and then began to decline.
“These findings suggest that a large portion of the vaccinated population may lose their protection against infection in the coming months, which may increase the potential for new epidemic waves,” the team wrote in a report published in the New England Journal of Medicine.
How can protection against mild or asymptomatic infection diminish while remaining strong against serious illness?
This is because the human immune system is complex.
Antibodies form the first line of defense that stops a virus from entering some cells in the body. This is the protection that starts to wear off over time.
But there is another line of defense — cell-based immunity. Cells called B cells and T cells may take longer to generate than antibodies, but they provide a longer lifespan, broader defenses against infection, and are responsible for decreases in serious infections.
So while people may be susceptible to mild illness after being vaccinated, they are much less likely to get really sick, end up in the hospital or die.
“But there are many reasons why people do not want to get sick. They will not give it to loved ones. People will not give it to young children who cannot be vaccinated yet,” Falsey said.
The US Centers for Disease Control and Prevention has been saying for months that this is why even fully vaccinated people should continue to take precautions against infection – wearing masks when they are around many other people who may or may not be vaccinated , especially indoors, and make sure the rooms are well ventilated.
“They just do not have to storm the pharmacies and panic.”
The people who got boosters now should have been among the first to be vaccinated – in January, February and March. They include people 65 years and older, adults with conditions that put them at risk of serious illness and people in occupations or living conditions that put them at a higher-than-average risk of infection.
Everyone else should cool it down for now.
“They just don’t have to storm the pharmacies and panic,” Falsey said.
People should not go ahead and get booster doses if it is not six months since their last dose of Pfizer vaccine because they will not get the best immune response, Fauci said in a briefing at the White House last month.
“For example, there will be temptations for people who have recently been vaccinated not to wait for a period of six months,” Fauci said. But waiting several months after the first immunization to increase helps produce a stronger response. Immune system cells that help restore weakened immunity respond more robustly if allowed to go into dormancy after the first round of vaccinations.
That said, most people should eventually plan on getting boosters, Falsey said.
“Probably that will be the case for any of the vaccines, not just Pfizer – we will benefit from boosting immunity. It is not the same as saying it is critically necessary,” she said.
While people who have recovered from an infection have some protection, they are even more protected if they are also vaccinated.
“I think depending on your own natural immunity, because you feel like you’re a strong person, it’s 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 just depend on my natural immunity to this virus. It’s a very, very bad actor,” Falsey said.