LONDON, Dec. 30 (Xinhua) -- All secondary schools and some primary schools in England will face delayed return when the new school term begins next week, the United Kingdom (UK) government said on Wednesday.

Education Secretary Gavin Williamson told the House of Commons that most primary schools will open as planned on Monday, Jan. 4, while all secondary pupils in exam years are to return during the week beginning Jan. 11.

Primary schools in a small number of areas with the highest infection rates will remain closed temporarily.

All secondary and college students will return to school full time on Jan. 18, he said.

According to the plan, during the first week of the new term, secondary schools and colleges will test as many staff and students as possible for coronavirus, and will only be open to vulnerable children or the children of key workers.

The government said a delayed return to schools is meant to "break the chains of transmission that are making infection rates shoot up."

"Because the COVID-19 infection rate is particularly high among this age group, we are going to allow more time so that every school and college is able to fully roll out mass testing of all pupils and students," Williamson said.

The British armed forces will remotely support mass testing of secondary school students in England and be on standby to provide in-person support at short notice if needed, the Ministry of Defence said on Tuesday.

Most of England was put into the toughest Tier 4 restrictions on Wednesday, which means a total of 44 million people will now be in Tier 4, or 78 percent of the population of England.

Meanwhile, the second COVID-19 vaccine has been authorized for use in Britain, allowing a significant expansion of the immunization program with hundreds of more vaccination sites opening in the coming weeks and months.

As the world is struggling to contain the pandemic, vaccination is underway in some countries with the already-authorized coronavirus vaccines.

Meanwhile, 232 candidate vaccines are still being developed worldwide -- 60 of them in clinical trials -- in countries including Germany, China, France, Russia, the United Kingdom and the United States, the World Health Organization reported on Dec. 29.