A year ago, only two doses of Covid-19 vaccine - or only one in the case of the Johnson & Johnson vaccine - were considered enough for high protection against coronavirus.
But then came Omicron. Most countries moved to a booster dose, with Israel becoming the first country to give a fourth dose.
Will this practice continue? Will we roll up our sleeves for a new dose every few months?
More than ten experts told the New York Times that, however the pandemic unfolds, revaccination every few months is not a practically realistic scenario, nor does it have a scientific basis.
"It is certainly not unheard of to give a vaccine periodically, but I think there are better solutions than booster doses every six months," said Akiko Ivashaki, an immunologist at Yale University."
Fading protection
A first problem is that many would be reluctant to stand in line for vaccinations so often. In the US, about 73% of adults have received the first two doses, yet only a third have chosen to receive a booster dose as well. In other countries, a significant proportion of the population has not even completed the initial vaccination.
So far, moreover, there is no data demonstrating the effectiveness of a fourth dose, at least in people with healthy immune systems.
Booster doses certainly boost antibody levels, but this boost is temporary. According to preliminary findings, antibodies begin to drop only a few weeks after the third dose. And, even when antibodies are at peak levels, the booster dose does not always prevent infection.
"Even with these antibody levels, it's very difficult to control the virus for very long," said virologist Shane Crotty of the La Jolla Institute of Immunology in La Jolla, California. "Perhaps an Omicron-specific vaccine would do a better job."
Allie Elbedy, an immunologist at the University of Washington in St. Louis, agreed with that assessment. "If you want to add another dose after three, I would certainly wait until an Omicron-based vaccine comes out," he said."
Other experts agreed that repeated use of a vaccine designed for the original pandemic strain doesn't make sense. A better solution would be a vaccine that targets stable parts of the virus and prevents all coronaviruses. Also under development are vaccines administered through the nose and mouth, which may prove more effective because they arm the tissues that first come into contact with the virus with antibodies.
Adequate protection against hospitalization
All experts who spoke to the New York Times agreed that a third dose is essential. But the fourth dose probably doesn't make sense since, despite the drop in antibodies, the immune system's T and B cells offer adequate protection against severe disease and hospitalization.
Repeated booster doses might make sense if the vaccination prevented even asymptomatic infection to limit the spread of the virus. Omicron, however, has shown that this is not the case. The goal is no longer to prevent all infections but to prevent hospitalizations, which the first three doses seem to accomplish.
In addition, booster doses make sense to be given at the right time, when new strains appear. Many people who received the third dose in the autumn, before the onset of Omicron, are now vulnerable to the new variant because protection levels have declined.
In the case of influenza, vaccination is recommended immediately before the start of the seasonal flu season. If the coronavirus eventually stabilizes in a similar seasonal pattern, "then you can imagine a scenario in which we give booster doses before winter every year," says Scott Hensley, a University of Pennsylvania immunologist.
Moreover, there are experts who are concerned that frequent vaccinations may even be harmful due to the phenomenon of "paternal antigenic sin." In such a case, the immune system reacts well to the original strain, but not to subsequent variants.
"We already have enough evidence that this could be a problem," said Dr. Amy Sherman of Harvard University.
"We have certainly seen significant evolutionary steps in a short period of time."
Source: in.gr
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