Omicron infection also produced immunity against Delta. This means someone who has been infected with delta is largely immune to subsequent delta infection. Therefore delta will soon have no one to infect, therefore will go away.
Omicron infection enhances neutralizing immunity against the Delta variantOmicron infection enhances neutralizing immunity against the Delta variant
https://www.ahri.org/wp-content/uploads/2021/12/MEDRXIV-2021-268439v1-Sigal_corr.pdf
Africa Health Research Institute, Durban, South Africa
School of Laboratory Medicine and Medical Sciences, University of KwaZulu-Natal
Omicron has been shown to be highly transmissible
Omicron has extensive evasion of neutralizing antibody immunity,
elicited by vaccination and previous SARS-CoV-2 infection.
Omicron infections are rapidly expanding worldwide often in the face of high levels of Delta infections.
Question
Do omicron antibodies neutralise delta virus variant?
Does neutralizing immunity elicited by Omicron also enhances neutralizing immunity against the Delta variant?
Method
Isolated the omicron and delta virus
Tested these against the plasma of 15 confirmed omicron cases
Used a live virus neutralization assay
(Vero E6 cells were propagated in complete growth medium)
Calculated the focus reduction neutralization test (FRNT50)
Volunteers
Previously vaccinated
Unvaccinated individuals who were infected with SARS-CoV-2 in the Omicron infection wave
Recruited soon after symptom onset
We then measured their ability to neutralize both Omicron and Delta virus at enrolment,
versus a median of 14 days after enrolment.
Neutralization of Omicron increased 14-fold over this time,
showing a developing antibody response to omicron
Also
Enhancement of Delta virus neutralization, increased 4.4-fold.
Therefore
The increase in Delta variant neutralization in individuals infected with Omicron may result in decreased ability of Delta to re-infect
Also
Emerging data indicating that Omicron is less pathogenic than Delta
Therefore
Cross immunity from omicron to delta may have positive implications in terms of decreasing the Covid-burden of severe disease.
More science
The ability of one variant to elicit immunity which can cross-neutralize another variant varies by variant
Immunity elicited by Delta infection
Does not cross-neutralize Beta virus
Immunity elicited by Beta infection
Does not cross-neutralize Delta well
Participants in this study
Many probably previously infected
More than half were vaccinated
Therefore activation of antibody immunity from previous infection and/or vaccination is possible
Implications
These results are consistent with Omicron displacing the Delta variant
As cross immunity makes re-infection with Delta less likely
(But previous delta exposure will not protect from symptomatic omicron infection)
If indeed Omicron is less pathogenic than Delta
The incidence of Covid-19 severe disease would be reduced
Infection may shift to become less disruptive to individuals and society
Source