Early evidence has shown that two doses of COVID vaccines are less effective against the Omicron variant than against previous variants like Delta. As a result, many countries have rolled out the booster doses. India will also begin the rollout of the third dose for health workers and the elderly from today (January 10).
The study, led by the UK Health Security Agency (UKHSA), estimates the effectiveness of three doses of either of Pfizer, Moderna and AstraZeneca's COVID-19 vaccines against mild and severe disease in adults aged 65 years or older. The study included individuals who reported symptoms and tested in community testing between November 27 and December 31, 2021. Vaccination rates in PCR positive cases were compared to vaccination rates in those who test negative.
The estimates suggest that effectiveness against symptomatic disease with the Omicron variant is significantly lower than compared to the Delta variant and wanes rapidly in those aged 65 years or older. But 2 to 9 weeks post the third dose of a COVID vaccine was associated with an 89 percent reduced risk of hospitalization among symptomatic cases with the Omicron variant among those aged 65 years or older.