Key
messages:
- WHO
has established the Technical Advisory Group on COVID-19 Vaccine Composition
(TAG-CO-VAC) to review and assess the public health implications of emerging
SARS-CoV-2 Variants of Concern (VOC) on the performance of COVID-19 vaccines
and to provide recommendations to WHO on COVID-19 vaccine composition, as
needed.
- In
the context of the circulation of Omicron SARS-CoV-2 Variant of Concern, the
TAG-CO-VAC urges broader access globally to current COVID-19 vaccines for
primary series and booster doses, in the hope that this also mitigates the
emergence and impact of new VOCs.
- The
TAG-CO-VAC is considering the strain composition of COVID-19 vaccines, and
encourages vaccine developers to gather data on a small scale on the breadth
and magnitude of immune response for monovalent and multivalent vaccines
against VOCs ? this data would then be considered in a broader decision-making
framework on vaccine composition by the TAG-CO-VAC.
---
In
September 2021, WHO established the Technical Advisory Group on COVID-19
Vaccine Composition (TAG-CO-VAC). This multidisciplinary group of 18 experts
reviews and assesses the public health implications of emerging VOCs on the
performance of COVID-19 vaccines and provides recommendations on COVID-19
vaccine composition.[1] The work of this group complements that of the
Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE), the Strategic
Advisory Group of Experts on Immunization (SAGE) and its Working Group on
COVID-19 Vaccines, and the working groups of the WHO R&D Blueprint for
Epidemics.
Since
its emergence, the SARS-CoV-2 virus has continued to evolve and WHO has
designated five variants as SARS-CoV-2 Variants of Concern (VOC) to date ?
namely Alpha, Beta, Gamma, Delta and Omicron ? due to their impact on
transmission, disease severity, or capacity for immune escape. While the
Omicron variant is spreading rapidly across the world, the evolution of
SARS-CoV-2 is expected to continue and Omicron is unlikely to be the last VOC.
The
TAG-CO-VAC is developing a framework to analyze the evidence on emerging VOCs
in the context of criteria that would trigger a recommendation to change
COVID-19 vaccine strain composition and will advise WHO on updated vaccine
compositions, as required. This framework considers the global spread and
transmissibility, clinical severity, genetic, antigenic and phenotypic
characteristics of the VOC, including capacity for immune escape and
assessments of vaccine effectiveness.[2]
Since
the WHO classified the Omicron variant as a VOC on 26 November 2021, the
TAG-CO-VAC has met regularly to review the evidence on the characteristics of
the Omicron variant. This statement reflects the current understanding of the
implications of the emergence of the Omicron variant on current COVID-19
vaccines and provides the TAG-CO-VACs current perspective on vaccine options
for the future.
Global
public health goals of COVID-19 vaccines
With
available COVID-19 vaccines, the current focus remains on reducing severe
disease and death, as well as protecting health systems. Vaccines that have
received WHO Emergency Use Listing, across several vaccine platforms, provide a
high level of protection against severe disease and death caused by VOCs. For
the Omicron variant, the mutational profile and preliminary data indicate that
vaccine effectiveness will be reduced against symptomatic disease caused by the
Omicron variant, but protection against severe disease is more likely to be
preserved. However, more data on vaccine effectiveness, particularly against
hospitalization, severe disease, and death are needed, including for each
vaccine platform and for various vaccine dosing and product regimens.
In
alignment with SAGE and its Working Group on COVID-19 Vaccines, the TAG-CO-VAC
therefore supports urgent and broad access to current COVID-19 vaccines for
priority populations worldwide to provide protection against severe disease and
death globally and, in the longer term, to mitigate the emergence and impact of
new VOCs by reducing the burden of infection. In practical terms, while some
countries may recommend booster doses of vaccine, the immediate priority for
the world is accelerating access to the primary vaccination, particularly for
groups at greater risk of developing severe disease.[3]
With
near- and medium-term supply of the available vaccines, the need for equity in
access to vaccines across countries to achieve global public health goals,
programmatic considerations including vaccine demand, and evolution of the
virus, a vaccination strategy based on repeated booster doses of the original
vaccine composition is unlikely to be appropriate or sustainable.
Composition
of current and future COVID-19 vaccines
The
TAG-CO-VAC considers that COVID-19 vaccines that have high impact on prevention
of infection and transmission, in addition to the prevention of severe disease
and death, are needed and should be developed. Until such vaccines are
available, and as the SARS-CoV-2 virus evolves, the composition of current
COVID-19 vaccines may need to be updated, to ensure that COVID-19 vaccines
continue to provide WHO-recommended levels of protection against infection and
disease[4] by VOCs, including Omicron and future variants.
The
TAG-CO-VAC will consider a change in vaccine composition:
- to
ensure that vaccines continue to meet the criteria established in WHO’s Target
Product Profile for COVID-19 vaccines, including protection against severe
disease
- to
improve vaccine-induced protection.
To
that aim, COVID-19 vaccines need to:
- be
based on strains that are genetically and antigenically close to the
circulating SARS-CoV-2 variant(s);
- in
addition to protection against severe disease and death, be more effective in
protection against infection thus lowering community transmission and the need
for stringent and broad-reaching public health and social measures;
- elicit
immune responses that are broad, strong, and long-lasting in order to reduce
the need for successive booster doses.
In
line with this approach, there are many options to consider:
- a
monovalent vaccine that elicits an immune response against the predominant
circulating variant(s), although this option faces the challenge of the rapid
emergence of SARS-CoV-2 variants and the time needed to develop a modified or
new vaccine;
- a
multivalent vaccine containing antigens from different SARS-CoV-2 VOCs;
- a pan SARS-CoV-2 vaccine: a more sustainable long-term option that would effectively be variant-proof.
In
the interim, the TAG-CO-VAC encourages COVID-19 vaccine manufacturers to
generate and provide data on performance of current and Omicron-specific
COVID-19 vaccines, including the breadth, magnitude, and durability of humoral
and cell mediated immune responses to variants through monovalent and/or
multivalent vaccines. These data will be considered in the context of the
framework mentioned above to inform the TAG-CO-VAC decisions when changes to
vaccine composition may be required. It would be important for vaccine
manufacturers to take steps in the short-term for the development and testing
of vaccines with predominant circulating variants and to share these data with
the TAG-CO-VAC and other relevant WHO expert committees. Vaccine manufacturers
are also encouraged to provide such data for any novel and broadly reactive
SARS-CoV-2 vaccines that are developed.
The
TAG-CO-VAC will continue to assess evidence on the predominant circulating
VOC(s) with respect to properties of spread/transmissibility, clinical severity
(virulence), genetic, antigenic and phenotypic characteristics of the VOC,
including capacity for immune escape and assessments of vaccine effectiveness
and impact, and information provided by manufacturers. The TAG-CO-VAC will then
advise WHO on COVID-19 vaccine strain composition, which could potentially be
developed either as a monovalent vaccine with the predominant circulating
variant or a multivalent vaccine derived from different variants.
Addressing
the challenge of continuing to ensure the production of the best possible
vaccines in a timely manner requires a continuous exchange of information and
collaboration between WHO and its expert groups, the TAG-CO-VAC, regulatory
authorities, and COVID-19 vaccine manufacturers. WHO, on behalf of its Member
States, is committed to facilitating this process.
This
statement and its conclusions will be updated by the TAG-CO-VAC as data become
available.
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[1] The functions of the TAG CO VAC are to:
Make
recommendations to WHO on the methods to assess the impact of Variants of
Concern (VOC) on vaccines;
Provide
interpretation of available evidence on the effect of VOCs on vaccines,
including but not limited to vaccine effectiveness; and
Recommend
to WHO, for each COVID-19 vaccine platform, adaptations (if any) needed so that
vaccines continue to safely provide WHO-recommended levels of protection
against VOCs.
[2]
Accounting for population demographics and prior vaccine or infection induced
immunity
[3]
Regardless of age.
[4]
The third version of the Target Product Profile for COVID-19 vaccines published
on 29 April 2020 is currently under revision.
Source:
WHO
Date: 2022-01-11