Third vaccine dose can boost effectiveness against Omicron to 88%, UK studies show

A third dose of COVID-19 vaccine can provide up to 88 per cent protection against hospitalisation from infection by the Omicron variant of coronavirus, according to early results from studies conducted in the UK. The findings compiled in a report by the UK Health Security Agency (UKSHA) show significantly higher protection provided by third vaccine dose against the highly mutated variant first identified in Botswana and South Africa in November, compared to two doses.

Eric Topol, professor of molecular medicine, and director of the Scripps Research Translational Institute in the US noted that vaccine effectiveness drops to 52 per cent against Omicron around six months after taking the second shot of a COVID-19 vaccine.

However, a booster dose substantially increases immunity and lowers the odds of being hospitalised with COVID-19 infection.

“That’s a big boost of protection for 3rd dose vaccine vs hospitalisation from Omicron infection. Vaccine effectiveness increased from 52 per cent (due to 2-dose waning after 6 months) to 88 per cent after the 3rd dose,” Topol tweeted on Sunday.

“It’s pretty impressive that vaccines directed to the ancestral strain spike from 2 years ago, with the virus that’s evolved through more than 290 million confirmed cases, and now to the hyper-mutated Omicron, have preserved efficacy of near 90 per cent vs severe disease with a 3rd shot,” he said in another tweet.

The UKHSA report cited two studies which examined the association between both variant and vaccination status and risk of hospitalisation.

The first study is based on approximately half a million Omicron cases, and includes all age groups while the second one uses a smaller dataset and is restricted to ages 18 and over.

The first study confirms the previous finding of reduced overall risk of hospitalisation for Omicron compared to Delta variant.

Both the studies found a substantial reduction in risk of hospitalisation for Omicron cases after three doses of vaccine compared to those who are unvaccinated.

Despite the estimated reduction in hospitalisation risk and preserved vaccine effectiveness against hospitalisation, the study authors noted that there may still be large numbers of admissions to hospital.

The risk of hospital admission from emergency departments with Omicron was approximately one-third of that for Delta.

The report shows that vaccine effectiveness against symptomatic disease continues to be lower for Omicron than for Delta with waning by 10 weeks after dose 3.

After three doses of vaccine, the risk of hospitalisation for a symptomatic case identified with Omicron through community testing was estimated to be reduced by 68 per cent when compared to similar individuals with the variant who were not vaccinated.

“Combined with the protection against becoming a symptomatic case, this gives a vaccine effectiveness against hospitalisation of 88 per cent (78 to 93 per cent) for Omicron after three doses of vaccine,” the UKHSA report added.