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The J&J COVID-19 vaccine: What you need to know

Updated 25 June 2021

The WHO Strategic Advisory Group of Experts (SAGE) on Immunisation has issued Interim recommendations for the use of the Janssen Ad26.CoV2.S vaccine against COVID-19.
Here is what you need to know.
This article provides a summary of the interim recommendations; the interim recommendations and the background document are also available.

Who should be vaccinated first?

While COVID-19 vaccine supplies are limited, health workers at high risk of exposure and older people should be prioritised for vaccination.

Countries can refer to the WHO Prioritization Roadmap and the WHO Values Framework as guidance for their prioritization of target groups.

Who else can take the vaccine?

The vaccine is safe and effective in people with known medical conditions associated with increased risk of severe disease, such as hypertension, chronic lung disease, significant cardiac disease, obesity, and diabetes.

Persons living with human immunodeficiency virus (HIV) are at higher risk of severe COVID-19 disease. This population group was included in clinical trials and no safety concerns were observed. It is recommended that known HIV-positive vaccine recipients be provided with information and counselling prior to vaccination. Further studies are needed to assess vaccine efficacy for persons with HIV; it is possible that the immune response to the vaccine may be reduced which would lower the vaccine’s effectiveness.

The J&J vaccine can be offered to people who have had COVID-19 in the past. But individuals may wish to defer their own COVID-19 vaccination for up to six months from the time of SARS-CoV-2 infection, to allow others who may need the vaccine more urgently to go first.

This vaccine can be offered to a breastfeeding woman who is part of a group recommended for the vaccination (e.g. health workers); discontinuing breastfeeding after vaccination is not currently recommended.

Should pregnant women be vaccinated?

WHO recommends the use of the COVID-19 vaccine in pregnant women only if the benefits of vaccination to the pregnant woman outweigh the potential risks. To help pregnant women make this assessment, they should be provided with information about the risks of COVID-19 in pregnancy, the likely benefits of vaccination in the local epidemiological context, and the current limitations of safety data in pregnant women. WHO does not recommend pregnancy testing prior to vaccination. WHO does not recommend delaying pregnancy or terminating pregnancy because of vaccination. While pregnancy puts women at higher risk of severe COVID-19, very little data are available to assess vaccine safety in pregnancy.

Who is the vaccine not recommended for?

Individuals with a history of anaphylaxis to any component of the vaccine should not take it.

Anyone with a body temperature over 38.5ºC should postpone vaccination until they no longer have a fever.

The vaccine is not recommended for persons younger than 18 years of age pending the results of further studies in that age group.

What’s the recommended dosage?

SAGE recommends the use of Janssen Ad26.CoV2.S as one dose (0.5 ml) given intramuscularly.

There should be a minimum interval of 14 days between the administration of this vaccine and any other vaccine against other health conditions. This recommendation may be amended as data on co-administration with other vaccines become available.

How does this vaccine compare to the dual dose vaccines already in use?

We cannot compare the vaccines head-to-head due to the different approaches taken in designing the respective studies, but overall, all of the vaccines that have achieved WHO Emergency Use Listing are highly effective in preventing severe disease and hospitalization due to COVID-19.

Is it safe?

SAGE has thoroughly assessed the data on quality, safety and efficacy of the vaccine and has recommended its use for people aged 18 and above.

This vaccine has also undergone review by the European Medicines Agency (EMA) and the U.S. Food and Drug Administration (FDA) and found to be safe for use.

How efficacious is the vaccine?

28 days after inoculation Janssen Ad26.CoV2.S was found to have an efficacy of 85.4% against severe disease and 93.1 % against hospitalization.

A single dose of Janssen Ad26.COV2.S was found in clinical trials to have an efficacy of 66.9% against symptomatic moderate and severe SARS-CoV-2 infection.

Does it work against new variants of SARS-CoV-2 virus?

SAGE has reviewed all available data on the performance of the vaccine in the settings of the variants of concern. In clinical trials this vaccine has been tested against a variety of SARS-CoV-2 virus variants, including B1.351 (first identified in South Africa) and P.2 (first identified in Brazil), and found to be efficacious.

SAGE currently recommends using this vaccine, according to the WHO Prioritization Roadmap, even if variants of concern are present in a country. As new data becomes available, WHO will update recommendations accordingly.

Does it prevent infection and transmission?

There is currently no substantive data available related to the impact of Ad26.COV2.S on transmission of virus that causes COVID-19 disease.

In the meantime, we must maintain and strengthen public health measures that work: masking, physical distancing, handwashing, respiratory and cough hygiene, avoiding crowds and ensuring good ventilation.


As of 25 June 2021, the Janssen vaccine is safe and effective at protecting people from the extremely serious risks of COVID-19, including death, hospitalization and severe disease.  More information is available in the updated SAGE interim recommendations which are available here. The 19 May statement of the WHO Global Advisory Committee on Vaccine Safety on the use of the Janssen (Ad26.COV2.S) also covers reports of very rare side effects. The Council for International Organizations of Medical Sciences classifies rates of adverse events or medicines and vaccines as follows:

  •  Very common > 1/10 
  • Common (frequent) > 1/100 and < 1/10 
  • Uncommon (infrequent) >1/1000 and < 1/100 
  • Rare> 1/10000 and <1/1000 
  • Very rare < 1/10000