‘Original antigenic sin’
Premature boosting could even be a handicap in the competition between immune response and virus, said Dr. Radbruch. This is due to the principle of “original antigenic sin.” If the immune system has already come into contact with a virus, contact with a new virus variant will cause it to form antibodies predominantly against those epitopes that were already present in the original virus. As a result of this, too many boosters can weaken protection against different variants.
“We have not actually observed this with SARS-CoV-2, however,” said Dr. Radbruch. “Immunity is always extremely broad. With a double or triple vaccination, all previously existing variants are covered by an affinity-matured immune system.”
Dr. Neumann-Haefelin confirmed this and added that all virus mutations, including Omicron, have different epitopes that affect the antibody response, but the T-cell response does not differ.
Dr. Radbruch said that the vaccine protection probably lasts for decades. Following an infection or vaccination, the antibody concentration in the bone marrow is similar to that achieved after a measles or tetanus vaccination. “The vaccination is already extremely efficient. You have protection at the same magnitude as for other infectious diseases or vaccinations, which is expected to last decades,” said Dr. Radbruch.
He clarified that the decrease in antibodies after vaccination and infection is normal and does not indicate a drop in protection. “Quantity and quality must not be confused here. There is simply less mass, but the grade of remaining antibody increases.”
In the competition around the virus antigens (referred to as affinity maturation), antibodies develop that bind 10 to 100 times better and are particularly protective against the virus. The immune system is thereby sustainably effective.
For whom and when?
Since the immune response is age dependent, it makes more sense to administer an additional booster to elderly people than to young people. Also included in this group, however, are people whose immune system still does not provide the same level of protection after the second or even third vaccination as that of younger, healthy people.
Dr. Radbruch noted that 4% of people older than 70 years exhibited autoantibodies against interferons. The effects are huge. “That is 20% of patients in an intensive care unit – and they all have a very poor prognosis,” said Dr. Radbruch. These people are extremely threatened by the virus. Multiple vaccinations are sensible for them.
Even people with a weak immune response benefit from multiple vaccinations, confirmed Dr. Neumann-Haefelin. “We are not seeing the antibody responses here that we see in young people with healthy immune systems until the third or fourth vaccination sometimes.”
Although for young healthy people, it is particularly important to ensure a sufficient period between vaccinations so that the affinity maturation is not impaired, those with a weak immune response can be vaccinated again as soon as after 3 months.
The “optimum minimum period of time” for people with healthy immune systems is 6 months, according to Dr. Neumann-Haefelin. “This is true for everyone in whom a proper response is expected.” The vaccine protection probably lasts significantly longer, and therefore, frequent boosting may not be necessary in the future, he said. The time separation also applies for medical personnel, for whom the Robert Koch Institute also recommends a second booster.