Four Covid-19 vaccines – those from Pfizer, Moderna, AstraZeneca and Johnson & Johnson – are currently available for use in Ireland, following their authorisation by the European Medicines Agency.

(The EU has also put in place purchase agreements with Sanofi-GSK and Curevac for vaccines currently in development, and is also in talks with two other vaccine producers, Novavax and Valneva, for potential supplies of Covid-19 vaccines in the future.)

Decisions about how to incorporate each inoculation in Ireland’s vaccine rollout have changed since the programme began, in January. So which one is best for you? The advice from public-health doctors and scientists is that “the best vaccine is the one that you are offered”.

Hospital Report

Pfizer–BioNTech vaccine, aka Comirnaty

Developed with the German company BioNTech, this is a messenger RNA, or mRNA, vaccine, which means it carries genetic instructions to produce a protein from Sars-CoV-2, the scientific name for the coronavirus that causes Covid-19. Your immune system recognises the protein as a foreign body and produces antibodies and activates T-cells (white blood cells) to attack it, giving you immunity to Covid-19.

Dose Two jabs, 21-28 days apart.

Efficacy 95 per cent. This means that clinical trials showed a 95 per cent drop in the number of symptomatic Covid-19 cases in people who received the vaccine compared with people who received a dummy injection.

Patient groups Patient Groups: The Pfizer vaccine was initially given to all those over 70 but with concerns about very rare side effects of the AstraZeneca and Johnson&Johnson vaccines and extra supplies of Pfizer vaccines now due, it will also be given to people under 50.

Common side effects Pain and swelling at the injection site; tiredness, headache, muscle and joint pains, chills, fever and diarrhoea.

Rare side effects Severe allergic reactions in a very small number of cases. People who already know they have an allergy to one of the components of the vaccine should not receive this jab.

Supplied to date More than a million Pfizer jabs have now been given, according to the Department of Health.

Further supplies Ireland is due to receive about 545,000 extra doses this week. More than 700,000 doses are expected in May, and more than 800,000 in June. A total of 5.4 million doses of this vaccine are expected to arrive for use in Ireland by the end of 2021.

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Moderna vaccine

Developed by Moderna, a Boston-based company, this vaccine is manufactured for EU countries at partner plants in Switzerland, France and Spain. Like the Pfizer jab, it is a messenger RNA, or mRNA, vaccine, which means it carries genetic instructions to produce a protein from Sars-CoV-2, the scientific name for the coronavirus that causes Covid-19. Your immune system recognises the protein as a foreign body and produces antibodies and activates T-cells (white blood cells) to attack it, giving you immunity to Covid-19.

Dose Two jabs, 28 days apart.

Efficacy 94 per cent. This means that clinical trials showed a 94 per cent drop in the number of symptomatic Covid-19 cases in people who received the vaccine compared with people who received a dummy injection.

Patient groups It was also initially given to the over 70s and healthcare workers and is now likely to be offered to those under 50 due to concerns about very rare side effects of both the AstraZeneca and Johnson&Johnson vaccines.   

Common side effects Pain and swelling at the injection site, tiredness, chills, fever, swollen or tender lymph nodes under the arm, headache, muscle and joint pain, nausea and vomiting.

Rare side effects Severe allergic reactions occur in a very small number of cases. People who have a severe allergic reaction when they are given the first dose should not receive the second dose.

Supplies to date About 110,000 doses of the Moderna vaccine were delivered to Ireland at the end of March. About 63,000 doses have been given so far.

Further supplies About 490,000 doses in total of the Moderna vaccine are expected before the end of 2021.

AstraZeneca–University of Oxford vaccine, aka Vaxzevria

Developed with researchers at the University of Oxford, this vaccine is being manufactured on a not-for-profit basis during the pandemic. It is a so-called viral vector vaccine based on a harmless common cold virus, or adenovirus, from a chimpanzee to which genetic material containing instructions for a protein of Sars-CoV-2. Once injected, your body produces this protein, which triggers an immune response that will respond to further attacks by Sars-CoV-2 and prevent you becoming ill with Covid-19.

Dose Two jabs, initially planned for 12 weeks apart and later changed to 16 weeks apart.

Efficacy 76-82 per cent according to AstraZeneca, 60 per cent according to the European Medicines Agency. A recent trial in South Africa showed that it has only 10 per cent efficacy against mild or moderate disease caused by the South African variant of Covid-19, B.1.351., which has halted its use in that country.

Patient groups Initially given to healthcare workers and people with underlying health conditions under 70, evidence of very rare blood clotting side effects resulted in the National Immunisation Advisory Committee (NIAC) recommending its use only for those aged 60 and over but updating this recommendation at the end of April to include those over 50.

Common side effects Tiredness, tenderness, bruising and pain at the vaccination site, headache, muscle and joint pain, nausea, diarrhoea or vomiting, fever.

Rare side effects Rare blood clots mainly in those under 50 (one in 100,000 people). This led to the Niac recommendation of its use only in people aged 60 or over, as other vaccines are available for the younger people. Those aged 60 or over are 85 times more at risk of dying from Covid-19 than getting one of the serious but very rare blood clots after the vaccine. The HSE recommends that anyone aged 60 or over who is on blood-thinning treatment or at risk of a blood clot for other reasons should still get the AstraZeneca vaccine.

At the weekend, the Health Service Executive's vaccine programme lead, Damien McCallion, said that people who refuse the AstraZeneca vaccine will not be eliminated from the rollout, but there are "no guarantees" about vaccine supplies downstream.

Supplies to date About 355,000 doses were delivered to Ireland by mid-April. Just under 285,000 jabs have been given so far.

Further supplies Estimated supplies (subject to change) are 1.4 million doses in May and 1.6 million doses in June.

Johnson & Johnson, aka Janssen vaccine

Also known as the Janssen vaccine because it is produced by the Belgium-based subsidiary of Johnson & Johnson, this is a viral vector vaccine that uses another virus, an adenovirus, that has been modified to contain the gene for the making of the Sars-CoV-2 spike protein. Your cells then produce these spike proteins, which your body in turn produces an immune response to.

Dose One jab.

Efficacy 57-72 per cent, depending on where clinical trials were held. The J&J vaccine had a 72 per cent efficacy in US trials, a 66 per cent efficacy in Latin American trials and a 57 per cent efficacy in South African trials; these results show how vaccine efficacy varies with new variants of Covid-19.

Patient groups Those aged 50 and over. And those under 50 for whom another vaccine is not available or for people in difficult to reach communities such as the homeless.

Common side effects Pain at the injection site, headache, tiredness, muscle pain and nausea.

Rare side effects Rare blood clots – one case per million doses – have been detected among people vaccinated in the United States.

Supplies to date 14,400 doses arrived in mid-April. At that point the company paused its rollout of vaccines to Europe following the detection of those very rare side effects in the US. A further 26,600 doses were initially scheduled to arrive in Ireland at the end of April.

Further supplies Ireland is expected to receive 545,000 more doses before the end of June, and a total of 2.1 million doses have been ordered to arrive by the end of 2021.