6 June 2024

In a move to reduce side effects from mRNA booster shots, the Public Health Ministry has given recipients three different COVID-19 vaccination options. The first is the full 30-microgram dose via intramuscular injection. The second is a half dose (15mcg) via the same method. And the third is a 10mcg dose via intradermal injection into the skin.

The three options are available from February 1, enabling people to choose the method they believe will have the least after-effects.

Common side effects of mRNA vaccines (Pfizer and Moderna) are redness and swelling around the injection site. Many recipients have also reported tiredness, headaches, muscle pain, chills, fever, and nausea.

A tiny proportion has developed serious side effects such as limb weakness, difficulty breathing, heart inflammation and even death.

Since May last year, the National Health Security Office (NHSO) has received more than 14,000 applications for compensation over COVID-19 vaccine side effects. More than 10,000 of the requests have already been approved, resulting in the NHSO paying out Bt1.22 billion so far.

Other than the mRNA types, there are also inactivated vaccines (Sinopharm and Sinovac), viral-vector vaccine (AstraZeneca) in Thailand.

What should you pick?

Virologist Dr. Yong Poovorawan, a prominent voice in Thailand’s COVID-19 vaccination drive, has advised that people can make an informed decision on their booster shot.

While the further study may be needed to identify which option is best for each individual, some information is already available.

A booster shot of Moderna contains just 50mcg or half the normal 100mcg dose in many countries. Research, including a study by the Yong-led Center of Excellence in Clinical Virology at Chulalongkorn University, shows 50mcg offers almost the same level of protection as 100mcg.

In Yong’s view, a higher dose may be more suitable for older people whose immune protection is generally lower than in youngsters.

Benefits of skin injections

Prof Dr. Thiravat Hemachudha, who heads the Thai Red Cross Emerging Infectious Diseases Health Science Centre, said it was good that Thais were being offered intradermal boosters since this method was safer and provided the same level of efficacy yet required less vaccine per shot compared to an intramuscular injection.

Side effects caused by an intradermal jab are generally 10 times lower than those caused by intramuscular injection. In most cases, recipients who opt for an intradermal shot will see swelling or redness at the injection site for just a few days.

Thiravat has been recommending intradermal injection since last year.

Thailand’s history with intradermal jabs

The COVID-19 vaccine is not the first jab to be administered into the skin or dermis. Three decades ago, hit by a shortage of rabies vaccine, Thailand became the first country in the world to administer the intradermal Rabies vaccine (IDRV). Records indicate IDRV was first studied as early as 1984. In 1992, the World Health Organization approved it for use in developing countries that were facing a shortage of rabies vaccines, including Thailand.

A study on intradermal injections of AstraZeneca vaccine in Phuket showed their efficacy was no lower than that of intramuscular injections, Medical Sciences Department director-general Dr. Supakit Sirilak said.

“But it will take more time before we can tell whether the protection lasts as long,” he added.

As such, Thailand has so far offered the intradermal option only for mRNA vaccines. This may change after more research on intradermal viral-vector AstraZeneca vaccine, and Sinovac and Sinopharm inactivated vaccines.

The race against Omicron

Thailand’s vaccination drive has made significant progress since its launch in March last year.

As of February 6, over 52 million people had received their first shot and 48.9 million had been jabbed at least twice. Meanwhile 15.4 million have already received their third shot.

Millions more will roll up their sleeves for the booster dose in the coming weeks, as the highly infectious Omicron variant drives a surge in new infections. The daily rate of new COVID-19 cases has soared past 10,000 for two days in a row now – a big jump from the few thousand per day seen in late December.

By Thai PBS World’s General Desk