The trajectory of cases attributed to the delta variant of SARS-CoV-2 suggests that the available vaccines do provide some protection against infection, but that the protection is time-dependent and wanes significantly. This observation is supported by the recent observation that anti-body levels in patients who had received the Sinovac injection are not durable. Here are a couple of thoughts related to this:
It is possible that because corona viruses are ubiquitous that the body's immunologic response to them as a class is not durable. Immunologic protection possibly wanes over time regardless of viral mutation or antigenic drift because that is how the human body is adapted to deal with ubiquitous viruses. Again, the data suggest although, of course do not prove, that the protection provided by vaccines has a half-life; hence the consideration of the need for "boosters" and perhaps yearly inoculations.
Measuring antibody levels as a marker of immunity is possibly a flawed strategy. It is perhaps the case that immunological protection depends more on T-cell response time rather the level of circulating antibodies at any one time.
Taking the above two conjectures together, it is quite possible that immunity provided by vaccines is enhanced by repeated exposure to circulating virus, and that vaccinated people would be better off foregoing any strategies, such as masking, that are intended to avoid contact with coronaviruses. For example, if a person receives a vaccine and has the desired immune response, but the protection afforded by the vaccine begins to wane in a few months (assuming that this is because that is the evolved response to coronaviruses), the immune response is likely to be enhanced by exposure to the virus that current immunity is sufficient to prevent active infection. This is possibly why epidemics peter out on their own, and why the avoidance strategies do not seem to work well at the population level. The vaccinate-and-avoid strategy may be counterproductive.
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