Vaccination against Covid reduces both the chance of catching Covid and the severity. Both provide arguments for vaccination, but different arguments. The first has so far been the main argument for pressuring people to get vaccinated, to reduce the infection rate and, hopefully, get us to herd immunity.
Unfortunately, protection against infections has turned out to be weaker than expected and diminishes substantially over time, which may help explain* why widespread vaccination has not led to a pattern of lower infection rates. Part of the reason may be behavioral. Vaccinated individuals are at much less risk of death or hospitalization, which may, probably does, lead them to be less careful to avoid contagion. And, because their cases are more likely to be asymptomatic, they are less likely to know they are contagious and take precautions against infecting others.
The most recent U.S. data on the new Omicron variety of Covid suggests that vaccination may provide no protection against it at all. Of cases identified so far, 79% were in fully vaccinated individuals, 21% in individuals who had also received booster shots more than two weeks before. For the U.S. population as a whole, about 60% are fully vaccinated, 15% have had booster shots. Judging by those numbers, vaccinated people, with or without booster shots, are more likely to get the disease, not less. The numbers are small enough so that could be chance variation and a more careful analysis should allow for different probabilities of a detected infection at different ages — children are both less likely to be vaccinated and less likely to get an infection serious enough to be detected than adults. But the numbers so far still suggest that vaccination provides little if any protection against catching the new variant. If so, the main argument for vaccine mandates is becoming increasingly irrelevant as Omicron spreads.
Whether or not vaccination provides protection against getting the virus, it provides substantial protection against hospitalization or death. While protection against infection seems to be down to something like 50% after a few months, protection against severe cases remains high; that is the main reason that death rates have been substantially lower, relative to infection rates, than before. That is a good reason for me to get vaccinated and get a booster, and I have. It is a much weaker reason for me to insist on other people getting vaccinated.
A weaker reason, but still a reason. Under our present medical system, part of the cost of hospitalization from Covid is born by the patient or his insurance company but not all. Especially if hospitalization for Covid gets high enough to crowd hospitals, as it has in a few parts of the U.S. but not yet most, my hospitalization imposes a significant cost on other people. As people become increasingly skeptical of claims that herd immunity is reachable if we just vaccinate enough people, the argument for vaccine mandates shifts to keeping the hospitals from filling up.
That is an argument for requiring the vulnerable elderly to be vaccinated — but most of them already are. It is a very weak argument for universal vaccination, especially for requiring children to get vaccinated. According to CDC figures, ages 0-17 have so far accounted for about one percent of all Covid associated hospitalizations. Protection against infection is an argument for requiring children to be vaccinated, since they can pass infection on to their much more vulnerable elders. Protection against hospitalization is not.
*The other explanation being the spread of the more contagious Delta variant.
A commenter on the version of this post on FaceBook points at a study that found no relation between level of vaccination and infection rates across both countries and US counties as of seven days before September 3rd, which suggests that the behavioral effect of vaccination may be strong enough to balance the vaccine's protection, at least that long after vaccination.