"the booster jab necessary for the Omicron variant in The Netherlands"
The booster jab is not mandatory in the Netherlands; it was not advertised as related to Omicron but was launched when Israeli studies revealed that the vaccine protection was waning after 6 months for all group ages but more dramatically for elderly populations (which NL has). This study was published in Israel last summer and it provoked their Booster campaign (not the 4th jab).
The US is still dealing with Delta, even though Omicron is now prevalent but the speed of diffusion in the US is much slower than in EU countries, due to size. During the first wave it followed the highways out of NY.