Intramuscular jabs prove more potent, study finds


New research has found that a third booster shot of the Covid-19 vaccine using the intramuscular injection (IM) technique induces a higher immune response than the previous intradermal (ID) technique, even though ID injections cause less severe side effects, a study by Siriraj Institute of Clinical Research has found.

IM shots directly penetrate the muscle, while the ID technique involves a more superficial injection into the skin.

Only one-fifth of the usual amount of the Covid-19 vaccine was used in ID injections in this study, which explained why it induced less robust immune responses and consequently fewer antibodies, according to the research team.

The study consisted of 210 people aged 65 and older who had previously received two shots of the AstraZeneca Covid-19 vaccine before receiving either the Pfizer or the Moderna vaccine as their third.

The Moderna vaccine induced a stronger antibody response against Omicron variants of the virus than Pfizer, according to the study.

Overall, the level of antibodies induced by ID injections of a third booster shot, especially of the Moderna vaccine, was found to be high enough to protect against severe symptoms and death.

Meanwhile, Dr Yong Poovorawan, head of the Centre of Excellence in Clinical Virology at Chulalongkorn University, has revealed that Thailand now has a new type of vaccine at its disposal.

Previously, Thailand has been using only inactivated, viral vector and mRNA vaccines, he said.

Now Thailand has the protein subunit vaccine Covovax from India, which has been patented and is produced using a similar approach to the US’s Novavax.

Covavax is produced by the Serum Institute of India under licence from Novavax and is part of the Covid-19 Vaccines Global Access (Covax) facility portfolio, giving a much-needed boost to ongoing efforts to vaccinate more people in lower-income countries, said the World Health Organization in a recent statement.

Another new vaccine in the pipeline is Covifenz, a plant-based virus-like particle Covid-19 vaccine which is made of tobacco leaves and produced by Medicago Inc in Canada, he said.