One in a hundred Dutch people has received a booster shot – considerably less than in our neighboring countries. The rate of injection is a subject of much discussion, especially now that the Health Council is advising all over 18s to get such a shot. What does a booster do, what’s in it, how often is it needed? Five questions and answers.
1 What exactly is a booster and why is an additional injection necessary?
In fact, the booster shot is a regular vaccination. He signals the immune system again to make antibodies against the virus. The antibodies bind to virus particles that enter the body and thus prevent an infection. A booster also stimulates other parts of the immune system, which develops further as a result.
It is now clear that the concentration of antibodies in the blood decreases within six months after the last corona vaccination. Protection against infection decreases from 88 percent to 47 percent in four to five months, according to research among 3.5 million Americans. The protection against hospitalization was still 93 percent after six months.
The Health Council therefore recommends the booster for all adults, starting with the elderly. Such a third injection brings the amount of antibodies in the blood back to the level immediately after the second vaccination. As a result, the vaccinated person is optimally protected again: on average, the vaccines protect 60 to 90 percent against infection immediately after vaccination, 94 percent against hospitalization and 97 percent against ICU admission. according to the latest figures from the RIVM.
2 Does a booster only help individuals, or does it also prevent spread?
Vaccinated people can still contract and spread the virus, even if they do not become ill themselves. Because they eliminate the virus more quickly, they are probably less contagious, but how much less is not yet clear. Recent American research suggests that vaccinated people who contract the virus have an equally high peak of virus particles, but that it lasts on average two days shorter. This suggests that they are also contagious for a shorter period of time. In that case, vaccination – and therefore also a booster shot – would not only protect individuals against disease, but also help contain the virus in society.
3 What is in such a booster shot?
The boosters are ‘regular’ corona vaccinations from Pfizer or Moderna. The Health Council recommends giving one of these two vaccinations, whatever someone’s previous vaccine was. From various studies, including an unpublished Dutch study, it appears that a booster shot with a different vaccine than the one someone has already been vaccinated with, also strengthens the immune response.
Protection against infection decreases from 88 percent to 47 percent in four to five months
In the Dutch study, more than 400 health workers who were fully vaccinated with Janssen (one shot), were given a booster with Janssen, Pfizer, Moderna or a placebo. Those who had received an mRNA booster (Pfizer or Moderna) had significantly higher concentrations of antibodies in their blood. Many people in healthcare institutions have been vaccinated with Janssen, and they can now be given extra protection with a booster containing one of the mRNA vaccines.
4 Have the booster shots already been adapted to the new virus variants?
New. All manufacturers are testing vaccines adapted to different combinations of variants, including Beta and Delta. But those adjustments are not yet included in the vaccines that are currently being administered. As far as we know, this is not necessary either: the current vaccines still work well enough, even against other variants.
Whether this also applies to Omikron is not yet known. All manufacturers are now investigating how effective their existing vaccines are against it. That is expected to become clear in the coming weeks.
Also read: Scientists are trying to unravel the Omikron variant in the lab
5 How often should people get a booster shot?
That’s not clear yet. For Dutch people who now receive a booster, there is half a year to a year between the previous and this vaccination. It is expected that the amount of antibodies will also gradually decrease after the booster vaccination. But it is not yet possible to say how bad that is. Not only the defense system thanks to antibodies is important, but also the functioning of white blood cells. That cellular defense is “trained” by the vaccine to fight the coronavirus. So-called B cells produce large amounts of antibodies as soon as a corona infection occurs. In addition, there are different types of T cells that recognize infected cells and quickly clear them.
A fully vaccinated person may therefore have fewer antibodies after a few months, but that does not mean that all immunity has disappeared: the trained immune cells can effectively fight an invading virus.
So it may well be that boosting every six months is not necessary. Perhaps an annual shot can help, just like the flu shot, or even that is not necessary, because our immune system is sufficiently trained after three vaccinations. This will become apparent in the coming years.
With the cooperation of Sander Voormolen and Niki Korteweg
A version of this article also appeared in NRC Handelsblad on 4 December 2021
A version of this article also appeared in NRC on the morning of December 4, 2021
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