What about those B cells and T cells?

All this talk about waning immunity from COVID-19 and the need for booster shots seems to me to be ignoring one important element. 

The talk is that the number of antibodies in vaccinated people is dropping drastically 6 or 7 months after vaccination. But, wait, isn't that exactly what we would expect? Isn't that what happens with pretty much all vaccinations? Well, yes, it is. But short-term antibodies are just one plank of the body's defences against infections.

While the effectiveness of neutralizing antibodies is starting to wane, the second line of defence - longer-term memory B cells and T cells - continues to be effective and even to strengthen. Memory B cells can rapidly deploy more antibodies in case of later exposure to the virus, and even to variants. T cells, on the other hand, can attack already-infected cells. This, not antibodies, is what will protect us against the coronavirus in the longer term.

All the indications are that the cellular immunity from the COVID-19 vaccines is pretty stable and robust at least six months after vaccination, and should provide good long-term protection against the virus and its variants, whatever the level of antibodies. Furthermore, a third booster dose of the vaccines may top up antibody levels temporarily (which may be useful during a resurgence in cases), but it will do little to increase our longer term B and T cell protection.

So, in that case, why are we seeing a rebound in cases in Europe, Asia and America? Well, that's partly because not everyone is vaccinated, partly because no vaccine us 100% effective, and partly because many countries have let their guards down in terms of masking, distancing, congregating, etc. As the experts have been telling us all along, the vaccines are a great boon but they are not a silver bullet, and other public health measures continue to be equally important (are you listening Alberta, UK, etc, etc?).