Chasing Elusive Virus

The XBB variant of the Omicron COVID virus lineage was the dominant cause of disease for most of 2023, and the new mRNA vaccines from Pfizer and Moderna released in September targeted this variant. Those of us that got one of these vaccines should be protected against serious consequence of COVID infection this winter.


A new report from Sweden (published in the British Medical Journal; BMJ 2023;383:e076990) examined the impact of prior vaccination on the incidence of long COVID in almost 300,000 vaccinated individuals compared with the same number of unvaccinated study participants. Protection against long COVID was dependent upon how many vaccine shots those in the vaccinated group had received. Protection was 21% for one dose, 59% for two doses, and 73% for three doses. Overall incidence of long COVID was 0.4% (1201/299,692) in the vaccinated cohort, a 70% reduction in risk compared to unvaccinated individuals. This is not a surprising result since prior vaccination reduces the risk of other serious consequences of COVID infection, but it is the first large study (required because of the low incidence of long COVID in this population) to document the level of protection. Yet another reason to keep getting new COVID vaccines (you did get at least 3 shots, right?).


The Omicron COVID virus lineage continues to evolve as it randomly mutates to evade immune responses. Much of the generation of new, immune evasive strains seems to take place during prolonged infection of individuals with some degree of impaired immune response. This was the origin of the original Omicron variant in South Africa in November of 2021 in a population with untreated or poorly treated HIV-1 infection. The XBB variant followed in late 2022, and now new COVID virus variants are appearing, as reported in a recent NY Times article (Carl Zimmer, NY Times, Nov. 21, 2023)


“In August, a variant called BA.2.86 emerged with a host of new mutations — likely the result, once again, of evolution taking place in an immunocompromised person. Over the past few months, however, the BA.2.86 lineage seems to have kicked into high gear, gaining a mutation that allows it to evade even more antibodies. JN.1, as this mutated form is known, has become the most resistant version of the coronavirus. It appears to be growing quickly in France, and it may soon spread to other countries.”


Because there are so many unvaccinated or immunocompromised hosts susceptible to new virus variants, continued evolution of the COVID virus is a certainty. Whether it will be JN.1 or a newer variant is uncertain, but it clear that COVID is here to stay and that a new vaccine formulation will be needed to protect against this ever changing virus.