The EU drug regulator is considering the need for coronavirus booster jabs while pandemic restrictions are tightened in parts of Vietnam and data suggests infection rates are rising in the UK.
The European Medicines Agency said on Monday it had started an expedited evaluation on whether to recommend a booster dose of the vaccine made by Pfizer-BioNTech.
The EMA said it was considering whether a third dose of the vaccine should be given six months after people 16 and older have received two doses, "to restore protection after it has waned".
EMA's experts are carrying out an "accelerated assessment" of data submitted by Pfizer and BioNTech, including results from an ongoing trial in which about 300 healthy adults received a booster shot about six months after their second dose.
Pfizer has already submitted an application to the US Food and Drug Administer for authorisation of a third dose and the US government said last month boosters would likely be available in late September.
Israel has already started administering booster doses and the plan is under consideration in other countries for vulnerable populations, including France and Germany.
The World Health Organisation has pleaded with rich countries not to use booster doses until at least the end of September, saying there is no scientific data that proves the shots are necessary.
It says COVID-19 vaccines would be put to better use in developing countries, which have received fewer than 2 per cent of the more than 5 billion doses administered.
The Amsterdam-based EMA said it expects to make a decision about whether or not to recommend a third dose of the Pfizer vaccine in the next few weeks.
Vietnam's capital Hanoi extended COVID-19 restrictions on Monday for a further two weeks as authorities launched a plan to conduct tests on the city's eight million people to try to curb a climb in infections that started in late April.
The country dealt successfully with the virus for much of the pandemic but the virulent Delta variant has proved more challenging in recent months.
COVID-19 has infected more than 536,000 people in Vietnam and killed 13,385, the vast majority in the past few months.
Hanoi, which has ordered people to stay home and halted all non-essential activities since July, has divided the city into "red," "orange" and "green" zones based on infection risk.
"People in quarantine camps, isolated areas or in red areas will be tested three times per week," city authorities said in a statement late on Monday, adding that people in other zones would be tested every five to seven days by either a PCR or rapid antigen test.
Barricades on Monday separated red zones from other areas, photographs posted on social media and media outlets showed.
Hanoi authorities are eager to keep the outbreak from reaching the intensity seen in Ho Chi Minh City, which accounts for nearly half of the total infections and 80 per cent of fatalities.
In the southern business hub, where a strict lockdown is in place until September 15, people have been encouraged to test themselves using antigen COVID-19 kits after health services were overwhelmed.
Official statistics indicate England's rate of new cases of coronavirus has started to rise once more.
The data showed 315.3 cases per 100,000 people were recorded in the seven days to September 2, the third day in a row the weekly rate has increased.
It means rates are up in three of the four parts of the United Kingdom, with only Northern Ireland registering a fall in cases.
Scotland is continuing to see a sharp rise in numbers, with 796.3 cases per 100,000 people recorded in the seven days to September 2 - up week-on-week from 644.8.
One month earlier, on August 2, Scotland's rate stood at just 142.8.
The rate for Wales currently stands at 479.6, up week-on-week from 411.8.
with Reuters and PA