Thread by @vipintukur

Delta & Omicron strains are the most globally relevant VOCs. While individuals infected with Delta are at risk to develop severe lung disease, Omicron infection causes less severe disease, mostly URT symptoms. 1/

The question arises whether rampant spread of #Omicron could lead to mass immunization, accelerating the end of the pandemic. 2/

A new study shows that infection with Delta, but not Omicron, induces broad immunity in mice. While sera from Omicron-infected mice only neutralize Omicron, sera from Delta-infected mice are broadly effective against Delta and other VOCs, including Omicron. 3/

This is not observed with the WA1 ancestral strain, although both WA1 & Delta elicited a highly pro-inflammatory cytokine response & replicated to similar titers in the respiratory tracts & lungs of infected mice as well as in human airway organoids. 4/

Pulmonary viral replication, pro-inflammatory cytokine expression, & overall disease progression are markedly reduced with Omicron infection. 5/

Analysis of human sera from Omicron & Delta breakthrough cases reveals effective cross-variant neutralization induced by both viruses in vaccinated individuals. 6/

Conclusions:

1-The study shows that while the Omicron virus is immunogenic, infection with this variant in unvaccinated individuals may not elicit effective cross-neutralizing antibodies against other variants. 7/

2-In vaccinated individuals, however, Omicron infection effectively induces immunity against itself & enhances protection against other variants. 8/

3-Delta infection is broadly immunogenic in mice, supports the inclusion of Omicron-and Delta-based immunogens in future multivalent vaccination strategies for broad protection against variants 9/

The above findings indicate that Delta may survive along with Omicron & we may have outbreaks of both!

Here is the preprint of the study👇 10/

medrxiv.org/content/10.110…

Earlier @sigallab confirms that an Omicron infection protects well against reinfection by Delta in previously vaxxed, but not so well in those that have not been previously vaccinated.
In unvaccinated people an Omicron infection only protects well against Omicron reinfection

https://twitter.com/sigallab/status/1483123897654517762

In a new study by @sigallab, they investigated whether neutralizing immunity elicited by Omicron infection would also neutralize the Delta variant & the role of prior vaccination. 1/

They enrolled South African participants infected with Omicron a median of 5 days post-symptoms onset (study baseline) with a last follow-up sample taken a median of 23 days post-symptoms onset. 2/

Some participants were unvaccinated while others were breakthrough cases vaccinated with Pfizer BNT162b2 or Johnson and Johnson Ad26.CoV2.S.

In vaccinated participants, neutralization of Omicron increased 13.7-fold over baseline. This compared to a 4.4-fold increase in unvaccinated individuals. 4/

Over the same period, Delta virus neutralization was enhanced 6.6-fold in vaccinated but only 2.5-fold in unvaccinated participants. 5/

Moreover, vaccinated participants were able to mount a stronger neutralization response against Delta relative to Omicron virus. 6/

This was not the case in unvaccinated individuals, some of whom continued to show low Delta neutralization, and contrasted sharply with poor cross-neutralization of Omicron in Delta infected persons. 7/

Higher Omicron neutralization in vaccinated individuals may enable a more effective immune response to Omicron, while enhancement of Delta neutralization should lead to lower Delta reinfections. 8/

Given emerging data indicating Omicron is less pathogenic than Delta, such an outcome may have implications in terms of decreasing Covid-19 severe disease. 9/

Here is the preprint of their new study👇
secureservercdn.net/50.62.198.70/1…