Third Dose Of Vaccine Can Boost Immunity Against Omicron By 88%: Study

Third dose builds a significantly stronger protective shield against the mutated strain when compared to the second dose, the effectiveness of which starts to wear off after six months.

Third Dose Of Vaccine Can Boost Immunity Against Omicron By 88%, Shows Study. (Representative Image/ Getty)

New Delhi: New studies in the UK have found that a third dose of the Covid-19 vaccine can boost a person’s immunity against the virulent Omicron variant by as much as 88%.

According to the studies, the third dose builds a significantly stronger protective shield against the mutated strain when compared to the second dose, the effectiveness of which starts to wear off after six months.

Sharing the report put together by the UK Health Security Agency (UKHSA) on the basis of the findings of these studies, Dr Eric Topol, professor of molecular medicine and director of the Scripps Research Translational Institute, said the vaccine effectiveness drops to 52% against Omicron around 6 months after the second dose.

However, a booster dose strengthens immunity by a significant margin, lowering the risks of contracting a fresh infection with severe symptoms that could result in hospitalisation.

“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,” Dr Eric Topol said in a tweet.

That's a big boost of protection for 3rd dose vaccine vs hospitalization from Omicron infectionhttps://t.co/gVl5c5o9nl
Vaccine effectiveness increased from 52% (due to 2-dose waning after 6 months) to 88% after the 3rd dose pic.twitter.com/c63Mpx8ClA

— Eric Topol (@EricTopol) January 2, 2022

The UKHSA report mentions studies pointing to a lower vaccine effectiveness against the Omicron variant as compared to the Delta strain. However, it indicates that the risk of emergency care or hospitalisation in the Omicron cases was significantly lower than Delta.

Moreover, the risk of hospitalisation is lower for the Omicron cases after a second and third dose of vaccine, with an average of 81% drop in hospitalisation risk after three doses as compared to unvaccinated patients.

A preliminary analysis further suggests that vaccinated school-aged children (between 5 and 17 years of age), who are infected with Omicron, have a lower risk of hospitalisation compared to the Delta cases.

With regard to symptomatic cases, the report says that the risk of hospitalisation in Omicron cases reduces by an average of 68% for those who have taken a third dose as compared to those 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 said.

The studies have also revealed that those who had received two doses of AstraZeneca (Covishield in India), did not show any effect against the Omicron five months after taking the second dose.

However, for those receiving two doses of Pfizer or Moderna, the vaccine effectiveness dropped from around 65% to 70% down to around 10% six months after the second dose.

"Two to four weeks after a booster dose, vaccine effectiveness ranged from around 65 to 75 per cent, dropping to 55 to 70 per cent at 5 to 9 weeks and 40 to 50 per cent from 10+ weeks after the booster," the report said.