I know the video. I've seen it. That's a load of old pony as well.
Here's his theory:
We have innate immunity including IgM antibodies that are non-specific and can neutralize all coronaviruses.
These antibodies are depleted as we get older.
They protect against symptomatic infection in young and healthy people, forming complexes with the virus while it is confined to the upper respiratory tract; these complexes are phagocytosed by antigen presenting cells, such as macrophages. Infected cells are destroyed by natural killer cells, also part of the innate immune system.
That is why some people test positive but only have mild symptoms.
While this is happening, the adaptive part of the immune system is making IgG antibodies, which are antigen-specific. In asymptomatically or mildly infected people, these are short-lived and are present in low quantities.
From what I can tell, these IgG antibodies help someone whose innate immune system can't deal with the infection. Someone who becomes severely sick but recovers, has these antibodies in larger quantities for much longer (6-8 months?).
During the first wave, the virus mainly infects people with low innate protection.
When this 'reservoir' of hosts is depleted, there is a period where infection is low. The virus needs to find a new reservoir and so infects younger and fitter people. These peoples' innate antibodies and NK cells can deal with the virus on first exposure. However, these fit and younger people also start mounting a short-lived adaptive response of IgG antibodies which, on second exposure, suppress their innate antibodies. This is because, being antigen-specific, they have higher affinity than the IgM for binding to the virus. So if a person's second exposure happens at a time when they still have a weak adaptive response from their first exposure, the innate IgM antibodies, having lower affinity than the antigen specific antibodies, can't bind to the virus and neutralize it. But because the adaptive response is weak, the IgG antibodies are not able to neutralize it either. And so the virus is able to infect and cause disease in these people. This is the second wave.
This wave continues while there are enough people whose short-lived adaptive response is suppressing their innate response. When this reservoir is depleted, the virus then turns back to the previously infected, elderly and vulnerable group whose long-lived antibody response from their first infection has by now waned. Since their innate immunity is also weak, the virus can use this reservoir for a third wave of infection.
After this, there is sufficient innate and adaptive immunity in the population for the virus to be suppressed to the extent that local outbreaks no longer spread throughout the population.
So that's the pandemic where no human intervention occurs.
Lockdown measures lead to low infection levels, but the virus can still spread in asymptomatic carriers and can therefore still mutate. Because these peoples' innate immunity is temporarily suppressed by their short-lived adaptive response, any mutations that overcome this response will out-survive the original strain and become dominant.
This enables the virus to compensate for the pressure caused by the lockdown. Soon infections rise, and you have a stronger second wave than would otherwise have occurred.
If we add vaccination to the picture, what happens is that the virus starts to encounter more short-lived antibodies in people after their first jab. Because it has increased its infectiousness due to the lockdown, it is able to escape these antibodies and continue to infect, so that it still has the chance to increase its infectiousness further through mutation. Potentially therefore it can mutate enough to evade the vaccinal antibodies completely.
Enter the booster jabs - but again, possibly too late to counter variants that have by that time evolved to evade them also.
So this is Geert Vanden Bossche's theory, as I understand it. I'm not qualified to say whether what he says about innate immunity suppression and immune escape is correct, and it doesn't much affect my choice on taking vaccination and boosters.
Video
here
