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Full info on the Janssen (J&J) COVID-19 vaccine

Posted by Eamonn Brady on

The single shot (Janssen) J&J vaccine against COVID-19

Part 2


Update on Vaccines for 18- to 34-year-olds

Since Monday 5th July, pharmacies including Whelehans Pearse St and Clonmore Mullingar can supply the Janssen single-dose Vaccine to 18 - 34-year-olds as well as over 50’s. You do not need to register on but you need an appointment with the pharmacy. There is currently a limited supply available. As more vaccines become available, we will be able to issue more appointments. Whelehans take bookings on the Whelehans website, but we must temporarily put bookings on hold until we get more supply in the coming weeks. Check our website for details.


Additionally, from Friday July 9th, the HSE vaccine portal at has been open to 30 to 34-year-olds so this age group will be able to register for other vaccines (including Pfizer) at vaccination centres with vaccinations starting in the coming weeks.


How efficacious is the vaccine?

28 days after inoculation Janssen (J&J) vaccine was found to have an efficacy of 85.4% against severe disease and hospitalization.


Does it work against new variants of the COVID-19 virus?

In studies released on July 1st, the Janssen vaccine showed excellent effectiveness against new Covid-19 variants including the Delta (Indian) and B1.351 (Brazilian) variant.


Protection for at least 8 months

New research, also released on July 1st shows the Janssen vaccine protects against serious illness from COVID-19 including new variants for at least 8 months, in fact, this immunity was shown to improve with time rather than wane.


Does it prevent infection and transmission?

There is currently no substantive data available related to the impact of the Janssen (J&J) vaccine on transmission of virus that causes COVID-19 disease.


Common side effects

More than 1 in 10 people may experience:

  • feeling tired
  • pain in the arm at injection site
  • headache
  • muscle pain
  • nausea


More than 1 in 100 people may have:

  • redness or swelling at injection site
  • joint pain
  • cough or a fever (temperature of 38 degrees Celsius or above)


Rare side effects

More than 1 in 1,000 people may have:

  • back pain
  • lack of energy
  • muscle weakness
  • pain in the limbs
  • pain in the throat
  • a rash
  • sneezing
  • sweating
  • a tremor


More than 1 in 10,000 people may have a red, itchy rash.


Very rare side effects

Very rarely, 1 in 300,000 people may develop very unusual blood clots with low platelets. 1 in 10 of these people may die. The risk of this very rare condition is higher in younger people, especially women. This side effect appears more common in people aged 18 to 49 and in women. Hence it was initially limited to over 50’s. Most people who got this very rare side effect got it within 14 days of getting the Janssen vaccine.


Get urgent medical help and mention your recent vaccination if you:

  • are breathless
  • have pain in the chest or stomach
  • have swelling or coldness in a leg
  • get a severe or worsening headache (particularly 3 or more days after the vaccine)
  • have blurred vision
  • feel confused
  • have seizures
  • have persistent bleeding under the skin where there was no previous injury
  • have many small bruises, reddish or purplish spots, or blood blisters under the skin


Serious side effects

Approximately 1 in 100,000 people have serious side effects like a severe allergic reaction after the Janssen vaccine. Your vaccinator is trained to treat serious allergic reactions. If these happen, it is usually soon after your vaccination. Hence you are asked to wait in the vaccination centre for 15 minutes after you have been vaccinated.


Fever after the vaccine

It is common to develop a fever (temperature of 38 degrees Celsius or above) within 48 hours of getting the vaccine. It usually goes away within 2 days. If you feel uncomfortable, take paracetamol or ibuprofen. If your fever lasts more than 48 hours or if you are worried, talk to your pharmacist or GP.


For the list of pharmacies offering COVID-19 Vaccination, check

COVID-19 Vaccines (J&J) are available through Whelehans Pharmacy, 38 Pearse St, Mullingar.  Log on to or dial 04493 34591 (Pearse St) to register your interest.

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