Much of the information , recommendations, observations opinions etc. regarding COVID is conflicting and confusing. One reason for this is that the certain subjects, such as immunity, are spoken of in vague and ambiguous terms. When someone speaks of immunity in one sense, such as herd immunity, it is countered by a counter-example which actually addresses a separate issue. To avoid this, it would perhaps be useful to define certain types of immunity. He are some suggestions:
1. Epidemic-limiting immunity. This type of immunity would limit and eventually end the epidemic. It is a population-level phenomenon, rather than an individual one. Vaccinations would be relevant to this type of immunity if the vaccines were highly effective in preventing both clinical disease and spread of coronavirus. Herd immunity would be the theoretical end point, although our understanding of herd immunity is likely an over-simplification. Our current experience with vaccines, re-infections, "breakthrough infections," "surges," and so forth suggest that the current batch of available vaccines have little effect on establishing this type of immunity.
2. Symptom-limiting immunity. This type of immunity is individual immunity that has the effect of decreasing the severity of disease in clinically apparent infections. The reason that it might be a useful distinction is because of the possibility that a person may have this type of immunity and still be able to transmit the infection. The current crop of vaccines do seem to provide temporary immunity of this type.
3. Mortality-limiting immunity. This is related to symptom-limiting immunity, but is potentially a meaningful distinction because different coronavirus variants may have different different mechanisms of causing death, or have disproportionate effects in different patient groups. For example, certain populations may be at increased risk of mortality if infected with COVID because of an increased risk of thrombotic complications. Others may be at greater risk of pulmonary or cardiovascular or renal complications. Furthermore, if the baseline mortality from COVID drops below a certain level, e.g. a case fatality rate of 0.5%, then this would affect the risk-benefit analysis of vaccination. It is difficult to tell if the current vaccines have significant effect on this type of mortality, although current data suggest that they do.
4. Infectivity-limiting immunity. This is similar to epidemic-limiting immunity, but is an individual phenomenon. It is worth considering separately because even if a vaccine were perfect at limiting symptoms and mortality, the individual immune response may be insufficient to limit viral replication and shedding. Thus, people could be asymptomatic spreaders, even if vaccinated, and vaccination would be an ineffective or relatively ineffective means of limiting the spread of disease. The current data seem to suggest that current vaccines, that target only the spike protein of the virus, do not provide this type of immunity.
Using the above a a guide, and referring to the earlier post on interpreting COVID data, it would appear that:
1. Current COVID vaccines provide temporary symptom limiting and mortality limiting immunity in the general population. It appears that these vaccines provide peak protection after approximately 5- 6 weeks, and that the immune protection is not durable; it begins to wane with a half-life of approximately 5 months, thus requiring booster vaccines, or ongoing exposure to live virus to maintain levels of immunity. The significance of this is that immunity of whatever type is time-dependent, and it is quite possible that people who had asymptomatic exposure to COVID have symptom, mortality and infectivity limiting immunity that is superior to someone who was vaccinated, but whose immunity has waned.
2. The current vaccines do not appear to be effective at limiting the spread of COVID, likely because they do not provide a sufficient immune response to suppress viral replication in infected individuals. The surge in cases in highly vaccinated populations such as the United Kingdom and Israel seem to be consistent with this hypothesis.
3. There is likely much more environmental influence on the behavior of the virus than the current mask and vaccinate strategies acknowledge. This would explain for example the different experiences between South Dakota and other states. It also makes fallacious the idea that case numbers are primarily influenced by policy interventions. Masking for example likely has very little influence on the number of hospitalizations due to COVID.
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