The idea of lowering immunity has picked up steam in recent weeks, with some countries using it to justify rolling out third-dose COVID-19 vaccine boosters to their populations. But immunologists say the concept is largely misunderstood.
While antibodies — proteins made after infection or vaccination that help prevent future invasion from the pathogen — level off over time, experts say this should happen.
And that doesn’t mean we’re not safe from COVID-19.
Jennifer Gommerman, an immunologist at the University of Toronto, said the term “coming down immunity” has given people a wrong understanding of how the immune system works.
“Wanning means that something is wrong and something is not,” she said. “It is very normal for the immune system to mount a response where a ton of antibodies are made and a lot of immune cells expand. And at the moment, that’s kind of occupied.
“But it has to be contracted, otherwise you won’t have room for subsequent immune responses.”
“When your immune system is charged up and ready to attack,” said Steven Kerfoot, associate professor of immunology at Western University, “antibody levels increase in the “primary response” phase after vaccination or infection.
Then they fall short of that “emergency phase,” he said. But the pathogen’s memory and the body’s ability to respond to it remain.
Kerfoot said B-cells, which make antibodies, and T-cells, which limit the virus’s ability to cause serious damage, continue to work together to ward off severe disease long after a vaccine has been administered. Huh. While T-cells cannot directly recognize the virus, they do determine which cells are infected and kill them quickly.
Recent studies have suggested that the T-cell response is still strong even several months after a COVID-19 vaccination.
“You might have a minor infection … (but) all those cells are still there, which is why we’re still seeing very stable effectiveness for preventing serious disease,” Kerfoot said.
A pre-print study released this week by Public Health England suggested that protection against hospitalization and death far outweighs protection against infection, even among older adults.
So the concept of reduced immunity depends on whether you’re measuring protection against infection or serious illness, Kerfoot said.
Ontario reported 43 hospitalization success cases on Friday among those fully vaccinated, compared to 256 hospitalized infections. A total of 795 new cases were reported in the province that day, of which 582 were among those who had not been fully vaccinated or had unknown vaccination status.
Meanwhile, British Columbia saw 53 fully vaccinated COVID-19 patients, compared to 318 uninfected patients hospitalized in the past two weeks.
“You’ll hear people say that vaccines aren’t designed to protect against infection, they’re designed to prevent serious disease,” Kerfoot said. “I wouldn’t necessarily say it’s the vaccine that’s designed to do one or the other… that’s just how the immune system works.”
Moderna released real-world data this week saying its vaccine was 96 percent effective at preventing hospitalizations, even among the more permeable Delta variant, and 87 percent at preventing infections. was effective – years below the 94 percent efficacy seen in previous clinical trials.
Moderna CEO Stephen Bunsell said the dip “reflects the impact of reduced immunity and supports the need for boosters to maintain a high level of protection.”
Pfizer-BioNtech has made the same argument with its own data, and an advisory panel from the US-based Food and Drug Administration recommended it for people age 65 and older or at high risk for serious disease. Voted on Friday to support the third dose.
However, the panel rejected the boosters for the general population, saying the drug company had provided little safety data on additional jabs.
Gommerman said the efficacy data presented by Moderna do not indicate a need for a third dose.
“The fact that it protects 87 percent against infection is unbelievable,” she said. “Most vaccines can’t achieve this.”
Bansel said Moderna’s research, which has yet to be reviewed, suggested that even a booster dose could increase the duration of an immune response by neutralizing antibody levels.
But Dr. Suman Chakraborty, an infectious disease physician in Mississauga, Ont., said just looking at the antibody response is misleading, and could be used incorrectly as a justification for an infinite number of boosters.
Israel, which has opened up a third dose to its citizens, recently spoke of a fourth dose in the near future.
“This idea of lowering immunity is being exploited and it’s really worth a look,” Chakraborty said. “There’s the idea that antibodies mean immunity, and that’s true… but the background level of immunity, the durable T-cell stuff, isn’t stressed enough.”
While some experts say that boosters for the general population are premature, they believe that some individuals will benefit from a third time.
The National Advisory Committee on Immunization recommends boosters for individuals who do not mount a strong immune response from a two-dose series.
Other experts have argued long-term care residents, who were given priority when the rollout began last December, may also need a third dose soon. The English study suggests that immunity may be lower in older groups, but not much – if at all – in people under 65.