Booster vaccinations for COVID-19

Booster vaccinations for COVID-19 for individuals who have been vaccinated with the Janssen vaccine without a history of previous COVID infection.

The goal of vaccinating individuals 16 years and older against COVID-19, which was set when the vaccination campaign began at the end of December 2020, has been achieved, as almost 90% of individuals of this age in Iceland have been vaccinated. Primary vaccination continues for those who have not already received the vaccination and those who move to the country unvaccinated or reach the age to receive vaccination according to marketing authorisation and the recommendation of the Chief Epidemiologist. The supply of vaccines according to delivery plans based on agreements made on behalf of the nation allows for consideration to be given to enhancing the response of certain groups through booster vaccination.

The first group that the Chief Epidemiologist recommends being offered a booster vaccination is individuals without history of COVID-19/antibodies who were vaccinated with the Janssen vaccine. This group will be offered one dose of Pfizer/BioNTech or Moderna vaccine at least 8 weeks after being vaccinated with the Janssen vaccine. The arguments behind this recommendation are as follows:

  • Protection after a single dose of Janssen vaccine is similar to protection after a single dose of other COVID-19 vaccines used in Iceland, about 66%1 against 74–80%2, 3, 4 protection against infection from the original Wuhan variant of the virus, but Janssen has a marketing authorisation as a single dose vaccine and was therefore used as such.
  • The protection from two doses of vaccines from Pfizer/BioNTech, Moderna or AstraZeneca is better than the protection of one dose.4, 5 The manufacturer of Janssen has tested a two-dose schedule in phase 1 & 2 trials using an 8-week interval. A second dose stimulated antibody response, but studies of the effects on the likelihood of infection are lacking.6 Longer-term studies of primary vaccination with two-dose vaccines for COVID-19 (Pfizer7 and AstraZeneca2 vaccines) have shown that the response is no worse and even better if the period between the first dose and the second dose is longer than originally planned by the manufacturers.
  • Other vaccines based on the same technology usually do not use the same vaccine for the booster dose as for the first dose (Janssen’s Ebola vaccine8 and the Sputnik V9 COVID-19 vaccine).
  • Studies on AstraZeneca’s COVID-19 vaccine’s stimulation, which is based on technology comparable to Janssen’s along mRNA vaccines such as the Pfizer/BioNTech and Moderna vaccines, have shown very good stimulation in terms of antibody production.10, 11
  • Very little information is available on the efficacy of the Janssen vaccine against the Delta variant of the SARS-CoV-2 virus, which has now gained the upper hand in Iceland as well as elsewhere, but information is available on the excellent efficacy of the Pfizer/BioNTech vaccine against this variant.12  
  • So far, during this 4th wave in Iceland, about 40% of those vaccinated who have been diagnosed with SARS-CoV-2 have been vaccinated with the Janssen vaccine. However, this should be interpreted with caution. The age group that is now most prominent in terms of infection, 18–49 years old, was largely vaccinated with Janssen, around 36%, but 21% of all vaccinated received the Janssen vaccine.
  • Many kindergarten and primary school teachers were vaccinated with the Janssen vaccine. As the Delta variant appears to have become widespread in the community, it is urgent to strengthen the protection of these professions before the start of the school year, especially given that children in kindergarten and primary schools have not been vaccinated in general vaccinations yet.


Arrangement: Vaccination appointments will be announced centrally from the vaccination system used for COVID-19 vaccinations based on the timing of the Janssen dose. The implementation will, as before, be carried out by the local healthcare centres.

1 (Janssen phase 3)

2 (AstraZeneca)

3 (Pfizer and Moderna)

4 (Moderna and Pfizer, a readable article with links to good research for both single and two doses)

5 (AstraZeneca)

6 (Janssen phases 1 & 2)

7 (Pfizer, from NHS in the UK)




11 unpublished data from the UK from the same study that the article on side effects was based on


Fyrst birt 10.08.2021

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