The Oxford/AstraZeneca (ChAdOx1-S [recombinant] vaccine) COVID … – World Health Organization

Updated on 13 June 2022 to ensure consistency of formatting.
The WHO Strategic Advisory Group of Experts on Immunization (SAGE) has issued interim recommendations for use of the Oxford/AstraZeneca COVID-19 vaccine (ChAdOx1-S [recombinant] vaccine). 
You may access the guidance document here
The vaccine is safe and effective for all individuals aged 18 and above. In line with the WHO Prioritization Roadmap and and the WHO Values Framework older adults, health workers and immunocompromised persons should be prioritised.
The Astra-Zeneca vaccine can be offered to people who have had COVID-19 in the past. But individuals may choose to delay vaccination for 3 months following the infection.
WHO recommends the use of the ChAdOx1-S [recombinant] COVID-19 vaccine in pregnant women only when 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.
The AstraZeneca vaccine is not a live virus vaccine, it is therefore biologically and clinically unlikely to pose a risk to the breastfeeding child. WHO does not recommend discontinuing breastfeeding because of vaccination.
People with a history of severe allergic reaction to any component of the vaccine should not take it.

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

The Global Advisory Committee on Vaccine Safety, a group of experts that provides independent and authoritative guidance to the WHO on the topic of safe vaccine use, receives and assesses reports of suspected safety events of potentially international impact.
A very rare adverse event called Thrombosis with Thrombocytopenia Syndrome (TTS), involving unusual and severe blood clotting events associated with low platelet counts, has been reported after vaccination with this vaccine. In countries with ongoing SARS-CoV-2 transmission, the benefit of vaccination in protecting against COVID-19 far outweighs the risks.
Guillain-Barré syndrome (GBS) has been reported very rarely following vaccination. However, a causal relationship with the vaccine has neither been confirmed nor ruled out and more rigorous studies are needed to fully assess the significance of these events. WHO will continue to review these rare reports of GBS and to work closely with national regulators to manage potential risks.
The AstraZeneca vaccine is safe and effective at protecting people from the extremely serious risks of COVID-19, including death, hospitalization and severe disease. Read the 16 April 2021 statement of the WHO Global Advisory Committee on Vaccine Safety on AstraZeneca COVID-19 vaccine for 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:
The AstraZeneca vaccine has an efficacy of 72% against symptomatic SARS-CoV-2 infection, as shown by the primary analysis of data irrespective of interdose interval from trial participants who received 2 standard doses with an interval varying from about 4 to 12 weeks. Vaccine efficacy tended to be higher when the interval between doses was longer.
The recommended dosage is two doses given intramuscularly (0.5ml each) with an interval of 8 to 12 weeks.
For countries that have not yet achieved high vaccine coverage rates in the high-priority groups and that are experiencing high incidence of COVID-19 cases combined with vaccine supply constraints, longer intervals i.e. up to 16 weeks can be considered. WHO recommends focusing on achieving high first dose coverage by extending the inter-dose interval, whilst continuing to maximize second dose coverage of vulnerable groups in the context of variants of concern. It should be noted that the full two dose regimen of this vaccine is believed to be more protective against variants of concern than a single dose alone.
Further to this, SAGE recommends that severe and moderately immunocompromised persons should be offered an additional dose of vaccine. This is due to the fact that this group is less likely to respond adequately to vaccination following a standard primary vaccination series and are at higher risk of severe COVID-19 disease.
A booster dose may be considered 4 – 6 months after completion of the primary vaccination series, starting with the higher priority-use groups, in accordance with the WHO Prioritization Roadmap.
The benefits of booster vaccination are recognized following increasing evidence of waning vaccine effectiveness against mild and asymptomatic SARS-CoV-2 infection over time.
The need for, and timing of, booster doses for children aged 5-11 years has not yet been determined.
SAGE accepts two heterologous doses of WHO EUL COVID-19 vaccines as a complete primary series.
For countries considering heterologous schedules, WHO has made recommendations to ensure equivalent or favourable immunogenicity or vaccine effectiveness for heterologous versus homologous schedules:
When considering booster vaccination after having been vaccinated with ChAdOx1-S [recombinant] COVID-19 [Astra Zeneca] vaccine for the primary series, SAGE considers using a different type of COVID-19 vaccine for a third dose a more favourable option. However, maintaining a homologous schedule is still acceptable.
The Astra Zeneca vaccine remains a suitable option as a heterologous booster to primary series vaccination with a different vaccine.
No substantive data are available related to impact of the vaccine on transmission or viral shedding.
In the meantime, we must maintain and strengthen public health and social measures that work: masking, physical distancing, handwashing, respiratory and cough hygiene, avoiding crowds, and ensuring good ventilation.
SAGE has reviewed all available data on the performance of the vaccine in the settings of variants of concern. SAGE currently recommends its use according to the WHO Prioritization Roadmap, even if virus variants are present in a country. Countries should assess the risks and benefits taking into consideration their epidemiological situation.
Preliminary findings highlight the urgent need for a coordinated approach for surveillance and evaluation of variants and their potential impact on vaccine effectiveness. As new data become available, WHO will update recommendations accordingly. There are no data yet for Omicron.
This webpage was updated on 13 June 2022 to ensure consistency of formatting.
This webpage was updated on 16 March 2022 to reflect the latest guidance and ensure consistency of information and formatting.
This webpage was updated on 5 January 2022 to update the latest guidance and ensure consistency of information and formatting.
There will be no further updates to this page. For more information on Covid-19 vaccines

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