Can you explain why Fauci said with the vaccines we will have a lowered immunity against variations of the virus?
A) Fauci is an idiot. I really wouldn’t pay much attention to him
B) Without context, I’m going to assume he’s referring to the fact that certain variants (e.g. the Brazil variant P.1) have slight changes in their S protein which make antibodies that were produced against the April 2020 variant or original Wuhan SARS-CoV-2 virus less effective.
Think of the S proteins as little keys that normally fit into the locks on your cell membranes. Antibodies locks that bind to the keys on SARS-CoV-2 virions so they can’t gain access to cells (and also to make it easier for the immune system to clean them up). A slight change to that key means that the antibodies no longer fit quite as well. If you throw enough of them at it, eventually one will “click” into place (i.e. bind), but it takes more chances before it works.
This applies to both the vaccines and the antibodies produced following COVID-19 infection. The city of Manaus had been hit hard by the April 2020 variant of SARS-CoV-2 with something like 70% of the city having been infected. Then the P.1 variant came along and slammed the same city all over again. Why? The antibodies those recovered patients had didn’t quite fit the modified S protein, so they weren’t as effective. There’s an article on it here: https://www.thelancet.com/article/S0140-6736(21)00183-5/fulltext
It’s worth noting that the levels of antibodies in vaccinated people are very high, like with those who recovered from a severe COVID-19 infection. Those who had a mild or asymptomatic case of COVID-19 have been shown to have much lower levels of antibodies. That’s why the guidance is there to get vaccinated even if you’ve had COVID-19 already: it can provide additional protection against the other variants.
While the change to the S protein can make the antibodies less effective at binding, high enough levels can still provide a lot of protection. So if that vaccine is 95% effective against the April 2020 variant, it might be more like 83% or 87% effective against the Brazil or South Africa or India variants. But that’s still very good.