Second COVID booster: Who should receive it and when?


The more boosters the better? Data from Israel show that immune protection in elderly people is strengthened even further after a fourth dose. Karl Lauterbach, MD, German minister of health, recently pleaded for a second booster for those aged 18 years and older, and he pushed for a European Union–wide recommendation. He has not been able to implement this yet.

Just as before, Germany’s Standing Committee on Vaccination (STIKO) is only recommending the second booster for people aged 70 years and older, the European Medicines Agency (EMA) is recommending the fourth vaccination for everyone aged 80 years and older, and the United States has set the general age limit at 50 years.

Specialists remain skeptical about expanding the availability of the second booster. “From an immunologic perspective, people under the age of 70 with a healthy immune system do not need this fourth vaccination,” said Christiane Falk, PhD, head of the Institute for Transplantation Immunology of the Hannover Medical School (Germany) and member of the German Federal Government COVID Expert Panel, at a Science Media Center press briefing.

After the second vaccination, young healthy people are sufficiently protected against a severe course of the disease. Dr. Falk sees the STIKO recommendation as feasible, since it can be worked with. People in nursing facilities or those with additional underlying conditions would be considered for a fourth vaccination, explained Dr. Falk.

Complete protection unrealistic

Achieving complete protection against infection through multiple boosters is not realistic, said Christoph Neumann-Haefelin, MD, head of the Working Group for Translational Virus Immunology at the Clinic for Internal Medicine II, University Hospital Freiburg, Germany. Therefore, this should not be pursued when discussing boosters. “The aim of the booster vaccination should be to protect different groups of people against severe courses of the disease,” said Dr. Neumann-Haefelin.

Neutralizing antibodies that are only present in high concentrations for a few weeks after infection or vaccination are sometimes able to prevent the infection on their own. The immunologic memory of B cells and T cells, which ensures long-lasting protection against severe courses of the disease, is at a high level after two doses, and a third dose increases the protection more.

While people with a weak immune system need significantly more vaccinations in a shorter period to receive the same protection, too many booster vaccinations against SARS-CoV-2 are not sensible for young healthy people.

Immune saturation effect

A recent study in macaques showed that an adjusted Omicron booster did not lead to higher antibody titers, compared with a usual booster. In January 2022, the EMA warned against frequent consecutive boosters that may no longer produce the desired immune response.

If someone receives a booster too early, a saturation effect can occur, warned Andreas Radbruch, PhD, scientific director of the German Rheumatism Research Center Berlin. “We know this from lots of experimental studies but also from lots of other vaccinations. For example, you cannot be vaccinated against tetanus twice at 3- or 4-week intervals. Nothing at all will happen the second time,” explained Dr. Radbruch.

If the same antigen is applied again and again at the same dose, the immune system is made so active that the antigen is directly intercepted and cannot have any new effect on the immune system. This mechanism has been known for a long time, said Dr. Radbruch.


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