As yet another wave of increased COVID-19 cases, hospitalizations, and deaths rolls on, this one fueled by the newer Omicron subvariants BA.4 and especially BA.5, public health authorities are largely eschewing earlier measures such as mask mandates, stay-at-home orders, improvements to ventilation in buildings, and even continuing to track the disease, instead relying heavily on repeated doses of mRNA vaccines.
Indeed, while some low-income countries still haven’t been able to deliver primary vaccinations to high-priority individuals such as healthcare workers, roughly a dozen countries have rolled out a second booster—that is, a fourth dose—of the mRNA vaccines developed by Moderna or Pfizer/BioNTech to at-risk groups, including older people. Preliminary data from those countries has shown that this second booster is highly effective at preventing severe illness and death among those groups.
But questions remain about how and the extent to which the second booster fortifies the immune system against the ...
