MANILA (REUTERS) - Delivery to the Philippines of the first batches of a promised 17 million doses of Thai-made AstraZeneca vaccines has been delayed by several weeks and reduced in size, a Philippine presidential adviser said on Tuesday (June 1).

The delay raises questions about AstraZeneca's vaccine distribution plan in South-east Asia that depends on 200 million doses made in Thailand by Siam Bioscience, a company owned by the country's king that is making vaccines for the first time.

It was not immediately clear if other countries slated to received Thai vaccine exports would be affected by similar delays.

AstraZeneca and Siam Bioscience did not immediately reply to questions about production at the Thai plant.

Inside Thailand, questions about Siam Bioscience meeting production targets are extremely sensitive because King Maha Vajiralongkorn is the sole owner of the company.

Insulting Thailand's monarchy is a crime punishable by up to 15 years in prison.

Philippine presidential adviser Joey Concepcion, who has been coordinating vaccine procurement with the Philippine government and private sector, told Reuters that AstraZeneca had informed him that delivery of the first batch of 1.3 million doses would have to be pushed back from the third week of this month to mid-July and also reduced to 1.17 million doses.

Mr Concepcion said he was in touch daily with AstraZeneca and was told there were delays in Thai production.

"It is a new plant they are running... that is how it is when you start a new plant," he said.

He added that delivery of the Philippines' second batch of 1.3 million doses would also be reduced to 1.17 million and has been moved from next month to August.

Nearly four million people in the Philippines have received a first dose of a Covid-19 vaccine.

The Philippines is one of the worst-hit countries in Asia, with more than 1.2 million coronavirus cases and 21,000 deaths.

It aims to inoculate at least 50 million of its 110 million population this year.

Thailand's Siam Bioscience last year signed a technology transfer agreement with AstraZeneca to produce 200 million doses per year, with 61 million doses going to Thailand this year and the rest to other South-east Asian countries.

Thailand's mass vaccination campaign will kick off next week with no clear indication about Siam Bioscience's production volume.

Public concern about vaccine access has grown in recent weeks as Thailand suffers its most severe Covid-19 outbreak yet.

Thai Health Minister Anutin Charnvirakul on Tuesday said the six million AstraZeneca doses due for this month would be delivered on time, but did not specify how many would be from Siam Bioscience as originally planned.

Thai police earlier this year laid criminal royal insult charges against opposition figure Thanathorn Juangroongruangkit, saying he had defamed the monarchy in a Facebook live stream when he accused the government of mishandling the vaccine campaign and of giving an unfair advantage to Siam Bioscience.

Thanathorn's case is pending trial.