Coronavirus vaccinations have started across the UK, bringing new hope to a country that has spent most of 2020 in fear of the disease.
Margaret Keenan, 90, was the first to receive the jab in the UK, having been given the life-saving vaccine at 6.31am in Coventry.
Since then, the vaccine has been given to several people in 50 hospitals across the country.
The UK government was unable to say how many people were vaccinated yesterday, but said information on numbers would be regularly released in due course.
Like all vaccines, the Covid-19 vaccine can cause side effects, although most are mild and go away within a few days.
The Joint Committee on Vaccination and Immunisation (the JCVI), an independent committee of experts that advises UK health departments on immunisation, set out its guidance ahead of a mass vaccination campaign that began this week as Britain received its first shipment of the Pfizer vaccine.
Children - under the age of 16
Children under the age of 16 won't be offered the Pfizer Covid-19 vaccine.
This is because there is a lack of evidence as to how it affects children - meaning it cannot be proved to be safe.
Unsurprisingly, the vaccine was tested on adults and older people and, as with pregnant women, there is a lack of data on the effects on kids.
Also, the vast majority of children who catch the coronavirus experience mild symptoms or are even asymptomatic - meaning they experience no symptoms.
That's according to the JCVI, who said further research is being carried out to understand the safety of Covid-19 vaccines in pregnancy and children.
It adds: "Following infection, almost all children will have asymptomatic infection or mild disease.
"There are very limited data on vaccination in adolescents, with no data on vaccination in younger children, at this time.
"The Committee advises that only those children at very high risk of exposure and serious outcomes, such as older children with severe neuro-disabilities that require residential care, should be offered vaccination.
"Clinicians should discuss the risks and benefits of vaccination with a person with parental responsibility, who should be told about the paucity of safety data for the vaccine in children aged over 16 years."
It adds: "As trials in children and pregnant women are completed, we will also gain a better understanding of the safety and effectiveness of the vaccines in these persons."
Pregnant women
Pregnant women or women planning a pregnancy should not receive a coronavirus vaccine because any potential risks are still unknown, new guidance says.
The JCVI updated its advice on priority groups for vaccination after the UK approved Pfizer's jab for emergency use this month.
The JCVI recommended pregnant women not come forward to receive the jab, writing: "There are no data as yet on the safety of Covid-19 vaccines in pregnancy, either from human or animal studies.
"Given the lack of evidence, JCVI favours a precautionary approach, and does not currently advise Covid-19 vaccination in pregnancy.
"Women should be advised not to come forward for vaccination if they may be pregnant or are planning a pregnancy within three months of the first dose."
It adds: "Data are anticipated which will inform discussions on vaccination in pregnancy.
"JCVI will review these as soon as they become available."
Women who are breast-feeding should also ask for advice from a doctor or pharmacist before getting the jab.
Deputy chief medical officer for England Professor Jonathan Van-Tam has said none of the vaccine trials deliberately included pregnant women, which is why there is a lack of information on the effects of the jab on this group.
Adam Finn, a professor of paediatrics at the University of Bristol, has told how this is normal practice.
Vaccines are typically not given to pregnant women because of the "very high need to avoid risk to the mother, the baby and the pregnancy."
Pregnant women will only receive vaccines if "there is evidence to support safety".
He added: "Equally there is a need to provide protection to pregnant women against infection – accordingly it is a priority to obtain the necessary information to confirm whether this is safe. But this takes time."
Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, said this does not mean scientists have found any evidence that the vaccine will cause pregnant women harm.
He said: "This is simply a lack of evidence on the balance of benefits and harms; it is not that there is evidence that harms outweigh benefits. If that were so, then there would be a specific contraindication [harmful in some way] against use in those groups."
The Professor explained that vaccines, as well as drugs and medicines, are only authorised for use once evidence of efficacy and safety has been found in groups to which they will be administered.
As there may be women who receive the vaccine while unaware they are pregnant, they will need to be followed up once they inform the NHS of their pregnancy.
Prof Evans added: "When enough have been followed, then the advice on use in pregnant women could be altered in the future when there is evidence that the balance of benefit with any possible harm is favourable, and women with a known pregnancy could then be advised to have a vaccination against Covid-19.
"Studies will have been done in animals and are still ongoing, and were there evidence of harm to a developing foetus, then a contraindication would be introduced".
People with allergies
UK regulators have issued a warning that people who have a history of “significant” allergic reactions should not currently receive the Pfizer/BioNTech Covid-19 vaccine.
The warning comes after two NHS staff members who received the Pfizer/BioNTech vaccine suffered an allergic reaction, the NHS in England has confirmed.
Both are recovering, it is understood.
The NHS in England said all trusts involved with the vaccination programme have been informed.
The Medicines and Healthcare products Regulatory Agency (MHRA) has given precautionary advice to NHS trusts that anyone who has a history of "significant" allergic reactions to medicines, food or vaccines should not receive the vaccine.
Professor Stephen Powis, national medical director for the NHS in England said: "As is common with new vaccines the MHRA have advised on a precautionary basis that people with a significant history of allergic reactions do not receive this vaccination after two people with a history of significant allergic reactions responded adversely yesterday. Both are recovering well."
Speaking to MPs, Dr June Raine, MHRA chief, said: "Even last evening we were looking at two case reports of allergic reactions. We know from the very extensive clinical trials that this wasn’t a feature but if we need to strengthen our advice now that we’ve had this experience in the vulnerable populations, the groups that have been selected as a priority, we get that advice to the field immediately."
Dr Raine said there would be “vigilance” “before, during and after” the vaccine is given.