The Department of Medical Sciences has found that administering an mRNA-based vaccine such as Pfizer or Moderna as a booster after initial doses of other vaccines like Sinovac and/or AstraZeneca produces a high level of immunity against both the Delta and Omicron coronavirus variants.
Department chief Dr Supakit Sirilak said data from a test involving 80 people showed that all Covid-19 vaccines produced low levels of immunity against Omicron when compared to Delta.
But immunity levels significantly increased after a booster dose from a different type of vaccine, especially an mRNA-based vaccine, Dr Supakit said during a press conference.
"The study shows we do need to get a booster vaccine for fighting against the Omicron variant," he said.
"I would like to recommend all people, especially those considered at high risk from the disease, to get a booster dose as soon as possible."
The study looked at immunity levels against both variants two weeks after test participants got a booster shot. The test was done under the Plaque Reduction Neutralisation Test (PRNT) method.
Results showed a very high level of immunity against the two variants.
According to the study, the level of immunity increased to 282.5 and 729.3 for Omicron and Delta respectively from two full doses of Sinovac followed by a booster shot -- using a smaller quantity -- of Pfizer.
A similarly effective result -- 222.9 and 691.1 -- was produced by two full doses of AstraZeneca followed by a booster dose of Pfizer.
In contrast, two shots of the same vaccine produced low levels of immunity against the Omicron strain -- 23.81 for AstraZeneca and 19.17 for Pfizer. Combining two shots of vaccines like Sinovac (inactivated virus) and AstraZeneca (viral vector) produced a level of just 11.63. No information on the efficacy of two shots of Sinovac was provided.
Dr Supaporn Phumiamorn, director of the Institute of Biological Products who conducted the study, said laboratory tests found Omicron would reproduce quite slowly compared with Delta, lowering its impact on the health of those infected with the new variant.
The Department of Medical Sciences is next going to study the length of valid immunity after vaccination, which will take some time to produce results.