Potential Resurgence of COVID-19 Pandemic with the Emergence of Omicron Variant
Hitting Omicron Where it Counts: A Comparison with Delta
In a preprint study published on MedRxiv, researchers used blood samples from individuals who had received AstraZeneca or Pfizer vaccines and live virus isolates. The findings suggest that the Omicron variant may pose a higher risk of infection, even for vaccinated individuals.
The study shows a significant drop in neutralizing titers, a measure of neutralizing antibodies generated in response to vaccination or COVID-19 infection. This raises concerns about the infection risk among previously infected or vaccinated people.
Despite the potential increase in infection rates, recent data indicates that Omicron may be less severe than the Delta strain. Scientists have found that Omicron replicates quickly in the upper airways but struggles to penetrate deep lung tissue. As a result, rates of severe pneumonia, hospitalization, and death among vaccinated populations could be lower compared to the Delta strain [5].
In some regions, such as southern California, Omicron infections are associated with a 51% lower risk of hospitalization and 91% lower risk of death compared to Delta [5]. However, in other regions, such as England, the reduction in hospitalization risk after excluding reinfections may be smaller (0–30%) [5].
ъThe latest variants, like XEC and NB.1.8.1, are not associated with increased severity. Hospitalization rates are dramatically lower for these variants, even across both vaccinated and previously infected populations [1]. This is likely due to widespread immunity from vaccination and prior infections, further reducing the risk of severe outcomes with the Omicron lineage variants [1].
It's worth noting that vaccinated individuals have higher overall antibody levels following infection with both Delta and Omicron compared to unvaccinated individuals [3]. However, Omicron-specific antibody and memory B cell responses are weaker, making Omicron more competent at immune evasion. Despite this, vaccinated individuals still retain some protection against severe disease [3].
Current booster vaccines, especially those updated to target Omicron subvariants (e.g., JN.1), provide substantial protection against severe illness. However, protection against symptomatic infection is lower (19%–49% in recent data) [1][4].
Additionally, Delta infections can still trigger new immune responses in vaccinated individuals, but Omicron infections do not elicit as strong a variant-specific response. This complicates long-term protective immunity [3].
To summarize, Omicron and its subvariants pose a reduced risk of severe illness, hospitalization, and death compared to Delta in vaccinated populations, mainly due to both reduced pathogenicity and broad population immunity [1][5][3]. It's crucial to note that, while the risk of severe disease is decreased, vaccinated individuals are still significantly less likely to experience severe illness or death [1][3]. Immunity from prior infection and vaccination has also helped to blunt the severity of current variants, with most infections being mild [1].
Scientists are exploring how the US medical community may address the lower risk of severe illness with Omicron, considering recent evidence suggests that vaccinated individuals could experience less severe symptoms compared to the Delta strain. In health-and-wellness discussions, it's important to consider additional measures for mitigating the spread of Omicron within vaccinated and previously infected populations, particularly in light of this variant's higher infectiousness.
