Thread by @sailorrooscout

A recent study out of South Africa 🇿🇦 shows:

Unvaccinated + Omicron = Immunity to Omicron ONLY

Vaccinated + Omicron = Immunity to Omicron, Delta, Beta, C.1.2, AND D614G!

Source for information above:
•medrxiv.org/content/10.110…

Researchers found Omicron-triggered neutralization is NOT extensively cross-reactive to VOCs, with 20 to 43-fold reductions in titer. In contrast, vaccination followed by “breakthrough” Omicron infection improved cross-neutralization of VOCs, with titers EXCEEDING 1:2900.

Details:
•Sera from hospitalized patients with mild to severe disease as per WHO definitions
•20 unvaccinated individuals, 7 vaccinated individuals (2 Johnson & Johnson, 5 Pfizer)
•No previous history of SARS-CoV-2 infection
•Most in the study were aged 50+

In the absence of vaccination, Omicron-elicited humoral responses, while potent against the matched Omicron spike, showed significantly LESS activity against VOCs. Thus, while highly immunogenic, Omicron does NOT elicit cross-neutralizing responses.

This is consistent with a decrease in the ability of plasma from unvaccinated individuals to neutralize Delta compared to Omicron following Omicron infection (see study linked below). This may result in risk of reinfection in this unvaccinated

https://twitter.com/sailorrooscout/status/1475831490655178756?s=21

group with other variants that continued to circulate and evolve in South Africa at the time of this study, albeit at low levels including Beta, Delta and C.1.2.

Further, while Omicron-based immunogens may be adequate boosters, they are UNLIKELY to be superior to existing vaccines for priming in SARS-CoV-2 naïve individuals.

On a not so separate topic. In regards to BA.2, those who recover from BA.1 will likely have strong cross protection against BA.2. If you’re interested in a study on this see: medrxiv.org/content/10.110…