Many media reports point to locations where health systems are being stretched by very high numbers of Omicron cases, in some cases partly because of health staff being either infected or isolated as contacts. However, there are a number of countries where despite case numbers surging, hospitalisation rates are lower during the Omicron wave.
Omicron reduces vaccine effectiveness overall but reduces to a much smaller extent against hospitalisation; boosters increase protection and T cell responses appear to be maintained. This figure shows hospitalisation ratios (proportion of confirmed cases hospitalised – Source: Airfinity).
The UK Health Security Agency analysis showed 89% effectiveness of boosters at protecting against hospitalisation.
Tseng et al pre-print: https://www.medrxiv.org/content/10.1101/2022.01.07.22268919v1.full.pdf
“…this study of mRNA-1273 found waning 2-dose VE against delta infection, high VE 3-dose VE against delta infection, and low 2-dose and 3-dose VE against omicron infection. Protection against omicron infection wanes within 3 months after dose 2, suggesting a need for a shorter interval between second and booster doses.”
A further article on neutralisation of Omicron (reduced, but significantly increased by boosting or by history of infection as well as full vaccination) here – Schmidt et al: https://www.nejm.org/doi/full/10.1056/NEJMc2119641
And a pre-print looking at T cell response to spike protein provides encouraging results – Keeton et al: https://www.medrxiv.org/content/10.1101/2021.12.26.21268380v1.full.pdf
“We assessed the ability of T cells to react with Omicron spike in participants who were vaccinated with Ad26.CoV2.S or BNT162b2, and in unvaccinated convalescent COVID-19 patients (n = 70). We found that 70-80% of the CD4 and CD8 T cell response to spike was maintained across study groups. Moreover, the magnitude of Omicron cross-reactive T cells was similar to that of the Beta and Delta variants, despite Omicron harbouring considerably more mutations…”
Also with some similar findings Tarke et al: https://www.biorxiv.org/content/10.1101/2021.12.28.474333v1.full.pdf
Very interesting on asymptomatic infection from Garrett et al: https://www.medrxiv.org/content/10.1101/2021.12.20.21268130v1.full.pdf
“…findings strongly suggest that Omicron has a much higher rate of asymptomatic carriage than other VOC and this high prevalence of asymptomatic infection is likely a major factor in the widespread, rapid dissemination of the variant globally.”
More on Omicron’s reduced colonisation of the lungs, quoting a number of animal studies all showing less severe illness with Omicron: https://www.nature.com/articles/d41586-022-00007-8
A pre-print study from Qatar on immune protection against Omicron from previous infection- Altarawneh et al: https://www.medrxiv.org/content/10.1101/2022.01.05.22268782v1.full.pdf
“Protection afforded by prior infection in preventing symptomatic reinfection with Alpha, Beta, or Delta is robust, at about 90%. While such protection against reinfection with Omicron is lower, it is still considerable at nearly 60%. Prior-infection protection against hospitalization or death at reinfection appears robust, regardless of variant.”
And an Israel study with real world case data showing effectiveness of third (booster) mRNA vaccine doses (but with more data required to asses longevity of protection) – Spitzer et al: https://jamanetwork.com/journals/jama/fullarticle/2788104
The requirement for a pre-departure test to arrive in England was to be scrapped from 7 January, as with the rules requiring visitors to self-isolate on arrival until they receive a negative PCR result. ”We will be… returning instead to the system we had in October last year, where those arriving in England will need to take a lateral flow test no later than the end of day two and, if positive, a further PCR test to help us identify any new variants at the border,”
Best wishes to all. The WHO Emergency Committee on COVID-19 meets again in a couple of days. I expect to update after that.
IATA Medical Advisor