British health authorities have urged more pregnant women to get coronavirus jabs after a national study found the Delta variant appeared to increase their risk of severe symptoms.
England's top midwife urged pregnant women to get the jab as new data showed an increase in severe illness among pregnant women hospitalised with virus symptoms.
Jacqueline Dunkley-Bent, chief midwifery officer for England, wrote to GPs and midwives urging them to encourage expectant mothers to get a jab.
She said she was calling on pregnant women to "protect themselves and their babies".
The Royal College of Obstetricians and Gynaecologists (RCOG) and the Royal College of Midwives have also recommended vaccination of pregnant women.
Public Health England has said it recommends pregnant women get Moderna and Pfizer vaccines because they have been given to over 130,000 pregnant women in the US.
A paper based on national data compiled by the UK Obstetric Surveillance System, published online on 25 July, found that the proportion of pregnant women admitted to hospital with moderate to severe infection rose "significantly" after the Delta variant became dominant in May.
The paper by University of Oxford researchers found that pregnant women hospitalised during the Delta wave were more likely to get pneumonia, with a third requiring respiratory support.
"It is very concerning that admissions of pregnant women to hospital with Covid-19 are increasing and that pregnant women appear to be more severely affected by the Delta variant of the disease," said the study's chief investigator Marian Knight, professor of maternal and child population health at the University of Oxford.
None of more than 3,000 pregnant women admitted to hospital with virus symptoms since February was fully vaccinated, the study said.
The study did not look at pregnant women with mild infections who were treated outside hospital.
The UK has recommended vaccination of pregnant women since April but take-up has been very low compared to the general population, the paper said, blaming misinformation fuelled by changing advice early in the vaccine roll-out.
"The findings of this study strongly highlight the urgent need for an international approach to tackle this misinformation and improve uptake of the vaccine during pregnancy," it said.
A survey by the RCOG in May found that 58% of pregnant women offered the vaccine had declined it, with most saying they feared harming the baby or were waiting for more information on safety.
Euro 2020 final 'supercharged' infections
Meanwhile, the joint director of public health for Middlesbrough, Redcar and Cleveland, said the Euro 2020 final helped "supercharge" infections in the northeast of England.
The final saw Italy beat England on penalties at Wembley Stadium in London on 11 July.
Middlesbrough currently has the highest rate of new cases in England, although it is down sharply week-on-week from 1,421.5 cases per 100,000 people to 695.8.
The biggest fall was recorded by Redcar and Cleveland, which is down from 1,520.2 to 668.6.
With the areas to be offered enhanced support by the government to tackle its case rates, Mark Adams told BBC Radio 4's Today programme: "The rates tended to kick off just after the Euros football final - our three highest days were three-to-five days after that final, so I think our momentum was kind of picking up then and that event just supercharged it up to the unfortunate position we found ourselves in.
"But what we have seen over the last week is our rates have more than halved, and so even though everyone else's rates are coming down as well, our rates seem to be coming down very quickly.
"So I think areas like Middlesbrough, Redcar and Cleveland, and places you've seen in the northwest and further north in the northeast, are more susceptible to Covid because of the types of jobs that people do, the inability to work from home.
"Middlesbrough was cited in the ONS survey of being in the bottom 10 of areas where people are able to work from home."
Additional reporting PA