Americans with a weakened immune system who have received a third corona shot are recommended to get a fourth vaccination six months later.
The US health service CDC writes in the vaccination guidelines that the fourth vaccination can be of all approved vaccines.
In the United States, people with a weakened immune system already received the third shot in August. Because their immune system does not work properly, they did not build up sufficient resistance against the coronavirus with the first two injections. Therefore, the CDC does not see that shot as a booster but as part of the first vaccinations because the vaccine only provides sufficient protection after three shots.
According to the CDC, the shot can be given with the vaccines from Pfizer/BioNTech, Moderna or Janssen. It does not matter which drug is given the first three times. For example, if the first vaccination is done with Janssen, then it is the third shot. This is because that drug already provides more protection after one vaccination than the other drugs; a single dose is needed in normal situations.
A fourth shot is currently very unusual. A number of countries, including the Netherlands, have approved the third vaccination against the coronavirus. However, in the Netherlands, this booster is only for certain risk groups; not everyone can get the vaccination.