Philippine President Rodrigo Duterte speaks during a news conference in Davao City, the Philippines, April 9, 2018. File Photo: Xinhua

Chinese experts said that injections of COVID-19 vaccines in the buttocks may not affect the efficacy of the vaccines, but will probably cause muscle abnormalities in the butt, affecting its appearance, after the Philippine media said that their President Rodrigo Duterte will receive COVID-19 vaccines in his buttocks.

Duterte decided to be inoculated in private as he will be injected in his buttocks, the Inquirer reported, which made Chinese netizens wonder whether injections in the buttocks can be as effective as injections on upper arms, and why normally vaccines are injected on upper arms.

Chinese disease control and prevention authority previously said that the COVID-19 vaccines should be injected into the muscles on the upper arms where there are no wounds. 

Intramuscular injection on the upper arms is a normal method for drug or vaccine injection. 

A Chinese vaccine expert Zhuang Shilihe told the Global Times on Wednesday that the method has been widely used to inject common vaccines like hepatitis B vaccine as well as Diphtheria and Tetanus vaccines.

Zhuang noted that as previous clinical trials on COVID-19 vaccine candidates are all conducted through upper arm injection, no data is available to show how injection on buttocks would affect the efficacy of the vaccines.

"Buttock injection probably would not change the effect of the vaccine, but cause some risk of muscle abnormalities in the buttocks, affecting the appearance of the buttocks," Zhuang said, adding that another difference is the place that hurts would be the buttock rather than upper arm. 

COVID-19 vaccines can be injected on buttocks, but it's not as convenient as getting the shot in the upper arm and if not operated well, injections on buttocks probably would lead to muscle abnormalities, said a Beijing-based immunologist who asked for anonymity. 

The risk of muscle abnormalities is especially high on children, according to the anonymous expert.

Some experts said that injection on buttocks are barely used as there is a lot of fat at the buttocks, so blood circulation at the buttocks is not good and vaccines won't be absorbed well. 

"The big challenge is to convince the public to get vaccinated. It's unfortunate President Duterte has chosen his buttocks to be site for vaccination instead of the deltoid area like US [President] Joe Biden, Indonesian President Joko Widodo Singapore PM Lee Hsien Loong. It would be very inspiring!" Tony Leachon, former special adviser to the Philippines's National Task Force against COVID-19, said on Twitter on Tuesday.