The government has ramped up its coronavirus booster vaccine programme ahead of Christmas as the Omicron variant soars in the UK.
The window between the second Covid-19 dose and a third booster jab has been halved from six months to three, meaning millions of adults are now eligible for their vaccines.
It comes as an additional 1,691 Omicron cases were identified in the UK, bringing the total number of confirmed Omicron cases to 11,708 as of yesterday (Thursday 16 December), according to the UK Health and Security Agency.
Read more: How effective are the Pfizer and Moderna booster jabs against Omicron variant of Covid?
It's understandable that many will have questions about the booster jabs.
We've answered two common questions about how soon the Pfizer and Moderna boosters offer protection and their side effects below.
How long does it take for booster vaccines to work?
Vaccines expert Professor Adam Finn said protection from the booster vaccine comes relatively quickly because the body already recognises the vaccine.
The University of Bristol scientist predicted that booster shots take effect after around one week, but maximum levels of protection will be seen around two weeks after the vaccine is administered.
Prof Finn, who is also a member of the Joint Committee on Vaccination and Immunisation (JCVI), told BBC Breakfast: “It does come through very fast because you’ve got immunological memory, you’ve seen the antigen before from your previous doses, so the level of protection goes up pretty quick."
He added: “We generally look for the level of protection around two weeks, because that’s probably when you get to pretty much maximum levels, but already at a week your antibody levels will be much higher than they were before you had the booster. So it does get going pretty quick.”
Meanwhile, according to Pfizer’s own trial, receiving the Pfizer-BioNTech jab as a booster should provide strong protection against illness from Covid from seven days after it is administered.
The Moderna jab also uses molecular RNA (mRNA) technology like that of the Pfizer jab, which means it will work in similar ways.
What are the booster side effects?
How your body reacts can vary from person to person and vaccine to vaccine - but some side effects can be more severe than others.
Those who are thought to be experiencing side effects are encouraged to log them on the Coronavirus Yellow Card reporting site.
Below is the government data on the most to least common side effects.
Side effects of the Pfizer booster jab
Very common side effects of the Pfizer vaccine, which may affect more than one in 10 people, include pain or swelling of the injection site, tiredness, headache, muscle pain, chills, joint pain, diarrhoea and a fever.
Common side effects, which may affect up to one in 10 people, include redness at the injection site, nausea and vomiting.
Uncommon side effects, potentially affecting up to one in 100 people, include enlarged lymph nodes, feeling unwell, arm pain, insomnia, injection site itching, allergic reactions such as rash or itching, feeling weak or lack of energy/sleepy, decreased appetite, excessive sweating and night sweats.
Rare side effects, which could affect up to one in 1,000 people include temporary one sided facial drooping and allergic reactions such as hives or swelling of the face.
Side effects for which the frequencies cannot be estimated with the available data include severe allergic reaction, inflammation of the heart (myocarditis or pericarditis), extensive swelling of the vaccinated limb and swelling of the face (swelling of the face may occur in patients who have had facial dermatological fillers).
Side effects of the Moderna booster jab
Very common side effects of the Moderna vaccine, which could affect more than one in 10 people, include swelling/tenderness of the underarm glands on the same side as the injection site, headache, nausea, vomiting, muscle ache, joint ache and stiffness, pain or swelling at the injection site, feeling very tired, chills and fever.
Common side effects, which could occur in up to one in 10 people, include diarrhoea, rash on the body and rash, redness or hives at the injection site (some of which may occur at four to 11 days after the injection).
Uncommon side effects, which could affect up to one in 100 people, include itchiness at the injection site.
Rare side effects, potentially affecting up to 1 in 1000 people, include temporary one sided facial drooping (Bell’s palsy), swelling of the face (may occur in patients who have had facial cosmetic injections), dizziness and decreased sense of touch or sensation.
Side effects for which the frequencies cannot be estimated with the available data include severe allergic reactions with breathing difficulties (anaphylaxis), reaction of increased sensitivity or intolerance by the immune system (hypersensitivity) and inflammation of the heart muscle (myocarditis) or inflammation of the lining outside the heart (pericarditis) which can result in breathlessness, palpitations or chest pain.
When to call 111
For either booster vaccine, the NHS advises you to call 111 immediately if you experience any of the following symptoms around for days to four weeks after being vaccinated:
A severe headache that is not relieved with painkillers or is getting worse, a headache that feels worse when you lie down or bend over, a headache that's unusual for you along with blurred vision, feeling or being sick, problems speaking, weakness, drowsiness or seizures (fits), a rash that looks like small bruises or bleeding under the skin or shortness of breath, chest pain, leg swelling or persistent abdominal (tummy) pain.
If you're worried about receiving the booster jab, it's recommended to talk to your doctor - especially if you've previously had an allergic reaction to a vaccine, have a compromised immune system or have any other illness that may affect taking the vaccine.
