Key messages:

  • The principal ambitions of COVID-19 vaccination employing currently accredited vaccines go on to be to lessen hospitalization, intense disease and dying, and to guard overall health devices. The use of at present accredited vaccines based on the index virus (i.e. the
    virus that was identified from the very first scenarios of COVID-19 in December 2019) confers large stages of safety against severe disease results for all variants, which includes Omicron with a booster dose.
  • There has been ongoing and considerable virus evolution considering the fact that SARS-CoV-2 emerged in late 2019 and it is likely that this evolution will go on, ensuing in the emergence of new variants, specially all those with alterations in the spike protein. The
    trajectory of SARS-CoV-2 evolution remains unsure and the genetic and antigenic properties of future variants simply cannot still be predicted.
  • Offered the uncertainties of further evolution, it could be prudent to go after an additional objective of COVID-19 vaccination of obtaining broader immunity against circulating and rising variants although retaining security versus critical condition and dying.
  • Readily available details (see Annex) indicate that the inclusion of Omicron, as the most antigenically distinctive SARS-CoV-2 Variant of Issue, in an up-to-date vaccine composition may well be useful if administered as a booster dose to these who have by now obtained a COVID-19 vaccination primary series. 

The Complex Advisory Team on COVID-19 Vaccine Composition (TAG-CO-VAC) is
an unbiased group of gurus that has continued to evaluate the community wellbeing implications of emerging SARS-CoV-2 Variants of Concern (VOC) on the efficiency of COVID-19 vaccines in buy to challenge well timed recommendations on possible modifications
to vaccine strain composition. Given that the designation of the Omicron VOC by the Globe Overall health Organization (WHO) in November 2021, the TAG-CO-VAC has closely adopted the impact of Omicron on the general performance of at present certified COVID-19 vaccines to
contemplate no matter whether a adjust in COVID-19 vaccine composition might be warranted­­­. Further to the interim statement posted on 8 March 2022, this TAG-CO-VAC assertion is supposed to offer Member States, vaccine
builders and regulatory authorities considerations as to whether or not a modified vaccine composition may be warranted and, if so, how this may possibly be achieved to fulfil the public overall health objectives of COVID-19 vaccination. 

Is a modified COVID-19 vaccine composition warranted?

Given that the classification of Omicron as a VOC, there has been speedy and relatively synchronous displacement of other circulating variants by Omicron that has brought about considerable epidemic waves in all 6 WHO regions. Omicron is characterised by a substantial selection of mutations, which include a lot of in antigenically important locations of the spike (S) protein. Its transmission benefit about other variants has largely been pushed by immune escape qualities, and Omicron has contaminated quite a few who experienced been earlier vaccinated and/or contaminated. Various sublineages inside of Omicron, notably BA.1, BA.2, BA.3, BA.4 and BA.5, have been identified, which share many of the same S protein mutations.

In this context, the key plans of COVID-19 vaccination applying at present accredited vaccines continue to be to minimize hospitalization, extreme ailment and demise, and to shield health systems. A most important collection of at the moment accredited vaccines centered on the
virus that was identified from the initial cases of COVID-19 in December 2019 (termed the index virus e.g. GISAID: hCoV-19/Wuhan/WIV04/2019) confers lower concentrations of defense towards serious disorder outcomes for Omicron, when compared to prior VOCs. Nonetheless,
a booster dose of the presently accredited COVID-19 vaccines primarily based on the index virus seems to restore protection towards severe sickness and dying against at this time circulating variants (1) at ranges that stay acceptable (2).

Nonetheless, there has been considerable virus evolution, specially in the S protein, considering that the to start with circumstances of COVID-19 and it is very likely that this evolution will proceed, resulting in the emergence of new variants in the upcoming. There is uncertainty
about the timing of the emergence, extent of international circulation and antigenic attributes of potential variants. In this context, immunity elicited against as broad a selection of SARS-CoV-2 S protein antigens as probable may possibly be desirable to keep and
most likely boost security against upcoming variants. Hence, it may be prudent to pursue an more aim of COVID-19 vaccination to accomplish immune responses that each: 

  • elicit a increased breadth in the immune response from circulating and emerging variants, to boost security in opposition to these variants and
  • retain security from hospitalization, significant condition and death, and guarding wellness systems.

As such, a modified COVID-19 vaccine composition may be warranted to broaden immune defense from divergent SARS-CoV-2 S protein antigens.

If a modified COVID-19 vaccine composition is considered to be vital, what is the recommended strain composition of the vaccine?

The TAG-CO-VAC has regarded as the comparative epidemiological and virological characteristics of VOCs to day, which include Omicron. This bundled, but was not restricted to, printed and unpublished knowledge on the antigenic qualities and antibody escape
of different VOCs including Omicron, the cross-security of Omicron specific responses next vaccination or an infection with prior VOCs, and pursuing Omicron infection and/or Omicron-precise vaccine candidates (see Annex). Importantly, the TAG-CO-VAC
acknowledges that at this time, minimal animal model and human data have been revealed on Omicron-particular vaccine candidates, and these will continue on to be reviewed as more knowledge develop into readily available.

Omicron is the most antigenically distinctive SARS-CoV-2 VOC to have unfold globally – a lot additional so than Alpha, or Delta, which are more antigenically related to the index virus. This has been shown by the considerably reduced neutralization
action towards Omicron as when compared to earlier VOCs, the two in vaccinated individuals and in those people who had been previously contaminated with earlier VOCs. In addition, antibody responses in formerly naïve (unprimed) folks uncovered to Omicron
are powerful, but they do not cross-react nicely with previous variants, such as other VOCs. In contrast, in folks who have been beforehand primed by SARS-CoV-2 an infection (i.e., index virus, Alpha, Delta) or COVID-19 vaccination (dependent on the
index virus), an infection with Omicron elicits a broadly cross-reactive antibody response. Comparable observations have also been seen in animal designs and preliminary medical info in individuals examining Omicron-particular vaccine candidates. Collectively,
the data show that recurring publicity to SARS-CoV-2 antigens (possibly by breakthrough infection, vaccination adhering to infection, or ≥ 3 vaccine doses) boosts the magnitude of the antibody response and an improve in breadth is noticed soon after
Omicron an infection in previously primed people. 

For that reason, obtainable information point out that the inclusion of Omicron in an up-to-date vaccine composition is possible to be effective in populations that have currently been given a COVID-19 vaccination key collection. For an Omicron-distinct vaccine product, the
TAG-CO-VAC acknowledges that viruses or viral genetic sequences really closely associated to hCoV/South Africa/NICD-N21668/2021 or hCoV/Usa/CA-CDC-4358237-001/2021 are some of the most antigenically distant from the index virus to day and are likely to
increase the magnitude and breadth of the antibody reaction.

Importantly, the TAG-CO-VAC considers that the protection provided by an Omicron-precise vaccine product or service is most likely to differ in individuals who have now obtained a COVID-19 vaccine principal collection (primed), as when compared to individuals who have not (unprimed). Based
on the details to day, it is inferred that an Omicron-certain monovalent vaccine item administered as a booster dose for people who have now been given a key vaccine collection may well elicit bigger breadth in the immune reaction.
In contrast, an Omicron-distinct monovalent vaccine products as a standalone formulation for the main sequence is not suggested as it is not however recognised whether or not Omicron-particular vaccines will offer you comparable
cross-reactive immunity and cross-defense from critical disease brought on by other VOCs in unprimed individuals as the index virus-dependent vaccines have carried out.

While bi- or multivalent merchandise have still to be authorised by regulatory authorities, vaccines made up of index virus and Omicron in a one product may perhaps be able to achieve comparable outcomes as the proposed sequential technique. On the other hand, at this time,
only restricted info are offered to evaluate no matter if the cross-reactive immune responses in individuals employing an Omicron-containing bi/multivalent product will be equal to these elicited with a sequential vaccine approach.

The TAG-CO-VAC recognizes that the inclusion of Omicron, as the most antigenically unique VOC to day, in a variant-specific formulation and administered as a booster dose, does not preclude the thing to consider of other variant-distinct formulations by
regulatory authorities. The key more aim of modified COVID-19 vaccine formulations is to accomplish breadth of cross-reactive immunity to past, at present circulating and/or emerging variants.


The use of now accredited vaccines based on the index virus confers significant levels of protection from serious sickness outcomes for all variants, which includes Omicron with a booster dose. As these types of, the continued use of now licensed vaccines for main
vaccination and as a booster dose is suitable to reach the principal targets of COVID-19 vaccination. Presented the uncertainties of the genetic and antigenic traits of foreseeable future SARS-CoV-2 variants, it could be prudent to pursue an further aim
of COVID-19 vaccination of accomplishing a greater breadth in the antibody response towards circulating and rising variants, while retaining defense against extreme condition and dying. In this context, available info indicate that the inclusion of
Omicron, as the most antigenically distinct SARS-CoV-2 VOC, in an up-to-date vaccine composition might be beneficial. Accessible details also point out that this would be very best administered as a booster dose to people who have previously received a COVID-19 vaccination
primary collection, if these vaccines were being to be manufactured accessible.

The TAG-CO-VAC acknowledges that this situation is based mostly on minimal info from animal designs, inference from Omicron an infection in primed and unprimed people today, and preliminary scientific information in people vaccinated with an Omicron vaccine applicant. The
TAG-CO-VAC thus acknowledges that appreciable uncertainties continue being. First of all, uncertainty in the trajectory of SARS-CoV-2 evolution is such that there is a threat that this update may perhaps not align with variants that emerge in the long term. Nonetheless, a
modified vaccine composition that features Omicron will very likely broaden the antibody reaction in primed folks. Secondly, there are assumptions as to the opportunity efficiency of variant-specific vaccines, such as Omicron-made up of vaccines.&#13
It is assumed that the basic safety, reactogenicity and immunogenicity of the current vaccine composition will be comparable to those people of the presently certified vaccines based mostly on the index virus. The TAG-CO-VAC for that reason strongly encourages the era
of scientific facts on immune responses in humans to a most important collection and/or booster dose of Omicron-unique vaccines, across distinctive vaccine platforms. These added knowledge might then be viewed as by TAG-CO-VAC and will make it possible for the Strategic Advisory Group of Professionals (SAGE) on Immunization and its COVID-19 Vaccines Performing Group to issue coverage recommendations on the
use and timing of Omicron-specific vaccines.

The assertion reflects the current vaccine performance and landscape of licensed COVID-19 vaccines as of June 2022. The assertion will consequently be current as further details develop into readily available.


1. WHO. COVID-19 Weekly Epidemiological Update. 8 June 2022. Available from:—8-june-2022


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