Protection against hospitalisation from COVID-19 vaccines is "good" against the Omicron variant of SARS-CoV-2, an analysis has found.
The risk for adults of being admitted to hospital with Omicron was approximately one third (Hazard Ratio 0.33, 95% CI 0.30 to 0.37) of that for the Delta variant, the UK Health Security Agency (UKHSA) said in a technical briefing.
The analysis also found that the risk of presentation to emergency care, or being admitted to hospital, with Omicron – whether testing for symptomatic or asymptomatic infection – was approximately half of that for Delta (Hazard Ratio 0.53, 95% CI 0.50 to 0.57).
Latest Government figures showed there were 14,210 patients in hospital in England with confirmed COVID-19 by January 3, the highest since February 20 last year, but lower than the peak of 34,336 recorded on January 2021.
Vaccine Effectiveness
The latest UKHSA data confirmed that the effectiveness of all COVID vaccines against symptomatic infection continued to be lower against Omicron compared with Delta.
No protection against Omicron was seen in people who had received the AstraZeneca vaccine from 20 weeks after their second dose.
Among those who had received two doses of the Pfizer/BioNTech or Moderna vaccines, effectiveness dropped from around 65-70% down to around 10% by 20 weeks after the second dose.
Two to 4 weeks after a booster dose, vaccine effectiveness ranged from around 65-75%, dropping to 55-70% at 5 to 9 weeks, and 40-50% from at 10 weeks or more after a booster dose.
The UKHSA worked with Cambridge University MRC Biostatistics unit to analyse 528,176 Omicron cases and 573,012 Delta cases up until 26 December.
The data suggested that three doses of vaccine were associated with an estimated 68% (95% CI 42% to 82%) reduction in the risk of being hospitalised with Omicron compared with people who were unvaccinated.
One dose of any vaccine was associated with a 35% reduced risk of hospitalisation among symptomatic cases with the Omicron variant, two doses with a 67% reduction up to 24 weeks after the second dose, and a 51% reduced risk 25 or more weeks after the second dose when compared to people who had not received a vaccine.
When the reduced risk of hospitalisation was combined with vaccine effectiveness against symptomatic disease, vaccine effectiveness against hospitalisation was estimated as:
- 88% (95% CI 78% to 93%) 2 weeks after a third 'booster' dose
- 52% at 25 or more weeks after dose 2
- 72% at 2 to 24 weeks after a second dose
- 52% after one dose
Preliminary analysis also suggested a lower risk of hospitalisation with the Omicron variant for school-age children, compared with Delta (Hazard Ratio 0.42, 95% CI 0.28 to 0.63).
Significant Pressure on the NHS 'Highly Likely'
Susan Hopkins, chief medical adviser at UKHSA, said: "The latest set of analysis is in keeping with the encouraging signs we have already seen.
"However, it remains too early to draw any definitive conclusions on hospital severity, and the increased transmissibility of Omicron, and the rising cases in the over 60s population in England, means it remains highly likely that there will be significant pressure on the NHS in [the] coming weeks."
Penny Ward, visiting professor in pharmaceutical medicine at King's College London, said that "we will need to wait until later in the New Year for this additional data, which, alongside case hospitalisation rate, will be critical to healthcare service planning over the early months of 2022".
Peter Openshaw, professor of experimental medicine at Imperial College London, commented: "This is really important new data that again confirms the vital importance of getting third dose – booster – vaccines. Omicron is a very highly infectious variant, and even if you think you can keep yourself safe by reducing contacts with others, it's now very unlikely that you can escape infection forever.
"This study adds to the now overwhelming evidence that three doses of vaccine provides good protection against severe COVID-19 caused by Omicron. It's a bit early to be sure, but it seems possible that some additional boosters will be needed."
