An analysis from the UK Health Security Agency has found that vaccine effectiveness against hospitalisation with the Omicron variant of COVID-19 is significantly lower than that against the Delta variant, and wanes rapidly

COVID-19 illustration

The protection against hospitalisation provided by COVID-19 vaccination is ‘good’ against the Omicron variant, an analysis has found.

In a technical briefing, the UK Health Security Agency (UKHSA) said that the risk for adults of being admitted to hospital with Omicron was approximately one-third (hazard ratio [HR] 0.33, 95% confidence interval [CI] 0.30–0.37) of that of the Delta variant.

The analysis also found that the risk of presentation to emergency care or admission to hospital with Omicron—whether for symptomatic or asymptomatic infection—was approximately half of that for Delta (HR 0.53, 95% CI 0.50–0.57).

The latest Government figures show that there were 14,210 patients in hospital in England with confirmed COVID-19 on 3 January 2022, the highest since 20 February 2021, but lower than the peak of 34,336 recorded in January 2021.

Vaccine effectiveness 

The UKHSA data confirm that the effectiveness of all COVID-19 vaccines against symptomatic infection continues to be lower against Omicron than against Delta.

No protection against Omicron was seen in people who had received the Oxford University–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% 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 5–9 weeks and 40–50% at 10 weeks or more after a booster dose.

The UKHSA worked with the University of Cambridge Medical Research Council Biostatistics Unit to analyse 528,176 Omicron cases and 573,012 Delta cases up until 26 December 2021.

The data suggested that three doses of a vaccine were associated with an estimated 68% (95% CI 42–82%) 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 with 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 at:

  • 88% (95% CI 78–93%) 2 weeks after a third, ‘booster’ dose
  • 52% at 25 or more weeks after a second dose
  • 72% at 2–24 weeks after a second dose
  • 52% after one dose.

A preliminary analysis also suggested a lower risk of hospitalisation with the Omicron variant for school-age children compared with Delta (HR 0.42, 95% CI 0.28–0.63).

Significant pressure on the NHS ‘highly likely’ 

Dr Susan Hopkins, Chief Medical Adviser at the UKHSA, said: ‘The latest … 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.’

Professor 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’.

Professor 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.’

This article originally appeared on Medscape, part of the Medscape Professional Network.

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