The World Health Organization (WHO) has updated its interim recommendations for the use of AstraZeneca’s ChAdOx1-S [recombinant] vaccine against SARS-CoV-2 (COVID-19).
Key Messages:
AstraZeneca COVID-19 AZD1222 – Vaxzevria, SII COVISHIELD™ are considered equivalent and interchangeable for both ChAdOx1-S [recombinant] doses.
Based on phase 3 trials, irrespective of inter-dose interval, ChAdOx1-S [recombinant] vaccine against COVID-19 has an efficacy of 72% (95% CI: 63-79%) against symptomatic SARS-CoV-2 infection.
A recent estimate of vaccine effectiveness against hospitalization with the Delta variant (B.1.617.2) was 71% (95% CI: 51-83%) after 1 dose and 92% (95% CI:75-97%) after 2 doses of ChAdOx1[recombinant] vaccine.
Vaccine effectiveness against hospitalization with the Alpha variant was 76% (95% CI: 61-85%) after 1 dose and 86% (95% CI: 53-96%) after 2 doses of ChAdOx1[recombinant] vaccine.
The vaccine is intended for use in people aged 18 years or more.
Phase 3 clinical trials demonstrated an efficacy against symptomatic COVID-19 of 85% (95% CI: 58–94%) in individuals aged 65 years or older. WHO recommends the vaccine for use in persons aged 65 years and older.
Vaccination is recommended for persons with comorbidities that have been identified as increasing the risk of severe COVID-19.
WHO recommends the use of ChAdOx1-S [recombinant] vaccine in pregnant women only if the benefits of vaccination to the pregnant woman outweigh the potential risks.
WHO does not recommend pregnancy testing prior to vaccination, and does not recommend delaying pregnancy or terminating pregnancy because of vaccination.
WHO recommends the use of ChAdOx1-S [recombinant] vaccine in breastfeeding women as in other adults, and does not recommend discontinuing breastfeeding because of vaccination.
Vaccination should be offered regardless of a person’s history of symptomatic or asymptomatic SARS-CoV-2 infection. Viral or serological testing for prior infection is not recommended for the purpose of decision-making about vaccination.
Persons with acute PCR-confirmed COVID-19, including occurrence in-between doses, should not be vaccinated until after they have recovered from acute illness and the criteria for discontinuation of isolation have been met. The optimal minimum interval between a natural infection and vaccination is not yet known.
The recommended schedule is two doses of 0.5 ml each administered intramuscularly into the deltoid muscle. While the manufacturer recommends administering with an interval of 4 to 12 weeks between the first and second doses, WHO recommends an interval of 8 to 12 weeks between the two doses.
If the second dose is inadvertently administered less than 4 weeks after the first, the dose does not need to be repeated.
If administration of the second dose is inadvertently delayed beyond 12 weeks, it should be given at the earliest possible opportunity.
Phase 3 clinical trial data show efficacy against symptomatic COVID-19 starts from 22 days after the first dose and thereafter is about 76% (95% CI: 59–86%) between days 22 and 90, prior to the administration of a second dose. Although binding antibody levels wane slightly by day 362, it is unlikely to be clinically significant.
After administration of the second dose, both vaccine efficacy and antibody titres are higher in individuals who had longer intervals between doses, comparing 8-12 weeks with < 6 weeks.
In vaccinees with the longer between-dose interval (≥12 weeks), efficacy at >14 days after the second dose was 81% (95% CI 60–91%), compared to 55% (95% CI: 33-70%) in those with an interval of <6 weeks.
There is little information on clinical protection beyond 12 weeks after a single dose.
Because ChAdOx1-S [recombinant] vaccines induce both a T cell and B cell response, it is likely that there is some degree of protection against clinical disease conferred by one dose beyond 12 weeks, in particular against hospitalization, severe disease, and death. However, data to confirm this are not currently available.
During an initial period of limited vaccine supply, prioritizing distribution of first doses of vaccine to as many highly vulnerable individuals as possible will avert more deaths than vaccinating fewer such people with two doses – so long as the effectiveness of a single dose against COVID-19 mortality is at least half that of two doses and does not wane below this level before receipt of the second dose.
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, particularly the Delta variant.
The optimal interval before offering second doses depends not only on vaccine effectiveness and waning but also on population vaccine coverage, supply projections, pre-existing naturally acquired immunity and country-specific vaccine prioritization plans.
There is currently no evidence indicating a need for further doses once an individual has received two doses.
With regards to using ChAdOx1-S [recombinant] products with other COVID-19 vaccines, it is currently recommended that the same COVID-19 vaccine products be used for both doses of the two-dose schedule. If different COVID-19 vaccines are
inadvertently administered in the two doses, no additional doses of either vaccine are recommended at this time.
There should be a minimum interval of 14 days between administration of ChAdOx1-S [recombinant] vaccine and any other vaccine against other conditions.
People who have an anaphylactic reaction following the first dose of this vaccine should not receive a second dose of the same vaccine. People who have had thrombosis with thrombocytopenia syndrome (TTS) following the first dose of this vaccine should not receive a second dose of the same vaccine.
In general, persons with an immediate non-anaphylactic allergic reaction to the first dose (i.e., urticaria, angioedema without respiratory signs or symptoms that occur within 4 hours of administration) should not receive additional doses, unless recommended after review by a health professional with specialist expertise.
Anyone with an acute febrile illness (body temperature over 38.5 ºC) should postpone vaccination until they are afebrile.
SARS-CoV-2 tests and vaccination:
Prior receipt of the vaccine will not affect the results of SARS-CoV-2 nucleic acid amplification or antigen tests for diagnosis of acute/current SARS-CoV-2 infection. However, it is important to note that currently available antibody tests for SARS-CoV-2 assess levels of IgM and/or IgG to the spike or the nucleocapsid protein. The vaccine contains the spike protein; thus, a positive test for spike protein IgM or IgG could indicate either prior infection or prior vaccination. To evaluate for evidence of prior infection in an individual who has received the vaccine, a test that specifically evaluates IgM or IgG to the nucleocapsid protein should be used.
A positive nucleocapsid protein-based assay indicates prior infection, while a negative nucleocapsid protein-based assay is expected after vaccination (unless a natural infection has occurred).
Useful Link:
Link to WHO’s updated interim recommendations:
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