Even though 12.7 billion doses of SARS CoV-2 vaccine have been given round the world so far, we should still welcome the new Omicron-specific vaccines as they have been specially tuned to the molecular signatures of the current variants of the SARS CoV-2 virus.
 
This means that they should be even more effective for the latest and most prevalent variants such as Omicron BA4 and BA5. These latest sub-variants account for more than 98% of all the world's current SARS CoV-2 infections.
 
Vaccines based on the original Wuhan variant (i.e. most) have not been particularly effective at stopping Omicron, hence the surges seen earlier in the year, they do however reduce the severity of the disease. The virus has been evolving -in fits and starts- for the last three years and continues to do so. The more infections there are the more likely the virus is to mutate, it’s just about probabilities.
 
At the moment the number of infections has dropped off globally, but we aren’t really monitoring that closely anymore - which is a mistake because we have seen infection rates drop off and then bounce back again with greater force.
 
The real reason for being vaccinated yet again with the Omicron-tuned vaccine is that we don’t know if there is going to be another virulent variant in the near future. I doubt if we will see more infectious variants (because the current Omicron is one of the most infectious disease agents known) but there is nothing to stop a more virulent form from being produced, i.e. one that creates more severe disease.
 
The new Omicron tuned vaccine will probably be more effective against the next versions of the disease (which will be Omicron derived) than previous vaccines, and that is a good enough reason to get boosted again (it’s insurance for the future).
 
The people who get the most severe effects of COVID-19 are, unsurprisingly, the unvaccinated or have let their immunity drop (even triple vaccination drops off by about six months), so boosters will always help and may be required for years to come. Age is less of an issue than it used to be, and of course, even young people can get long COVID.
 
The latest data shows that repeated infections also increase the chances of getting long COVID, which in turn increases the likelihood of diabetes and heart disease, so avoiding further infections is still important in the long term. That means regularly boosting protection with the best currently available vaccine. COVID-19 is with us for the foreseeable future and adapting to it requires long-haul vaccine vigilance for all of us.

ATAGI has given the approval for the first combination booster to be introduced to the COVID-19 vaccine program in Australia. The new booster produced by Moderna is called Spikevax Bivalent Original/Omicron – acts against the original strain of SARS-CoV-2 and the BA.1 Omicron variant lineages. These are also called bivalent vaccines, contain two components of the variants and are also known as an updated COVID-19 vaccine booster. 

The combination booster will be given to those over 18 years and has already been rolled out in the US, UK, EU, Canada and Switzerland. Interestingly the US is administering updated boosters that include mRNA components of the original strain and between the Omicron variant BA.4 and BA.5 lineages to provide better protection against COVID-19.  

Some features are: take it three months after your most recent booster, it can be administered with other vaccines and it is not to be used as a primary dose. It is important to reiterate that COVID-19 vaccines and boosters have been proven to protect against severe illness, hospitalisation and death, however, immunity decreases over time as the virus mutates.

The current Moderna bivalent vaccine being rolled out in Australia contains the Omicron variant BA.1 and the original strain of COVID-19. It is unclear how much additional protection this new vaccine will provide for those who have already had four doses of a COVID-19 vaccine and exposure to the virus. 

It is also unclear whether levels of neutralising antibody provided by this new formulation provide significant additional protection for the majority of the population as limited clinical data currently exists. 

Moderna and Pfizer have further bivalent vaccines designed to target the Omicron subvariants BA.4 and BA.5 as well as the original strain of COVID-19. 

Most of the available data on the effectiveness of these boosters has been obtained from animal studies alone which should be of some concern and really requires some understanding of neutralising antibody generated from both previous COVID-19 vaccination and infection with the virus. The message being relayed seems to be that further vaccination offers better protection but the evidence is still lacking to support this assumption.

Certainly, the argument can be made for these newer boosters in individuals who are immunocompromised but this needs to be balanced against the use of available COVID-19 drugs.

The new bivalent Moderna vaccine contains the BA.1 subvariant of Omicron in addition to an earlier strain of COVID-19. The main question that arises about this vaccine is how effective a vaccine containing BA.1 will be in Australia where the BA.5 subvariant is dominating. In other words, even though BA.1 and BA.5 are both Omicron, they are different subvariants, so will this vaccine be useful?

The trial data evaluating this new bivalent vaccine measured antibody levels. Not surprisingly, there is an antibody response to BA.4/BA.5 if you receive this new bivalent vaccine but it isn't as strong compared to the response to BA.1, for which the vaccine was developed. However, UK data examined the risk of hospitalisation with Omicron >15 weeks after a booster with the "old" mRNA vaccines that don't contain an Omicron subvariant. They found that these "old" vaccines still provided good protection against severe disease >15 weeks later.

Furthermore, mathematical modelling from Australia has shown that when around 50% of the population is immune to COVID-19 (akin to the situation here), an Omicron-specific vaccine doesn't add too much of a benefit over the mRNA vaccines that we have been using thus far. The take-home message would be that it is good to have the new BA.1 bivalent vaccine if you are eligible for a booster, as it is likely to give a slight benefit for severe disease over the current boosters in the current Australian COVID-19 climate. But the current mRNA boosters still do a great job too.