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Professor Christine Loscher Why boosters are so important in the fight against Omicron

Why do we care so much about boosters right now? Let’s look at how we got here.

LAST UPDATE | 18 Dec 2021

BEFORE 2020 MOST people didn’t think too much about vaccines unless they had a baby or were going on holidays to exotic lands. And before the summer of 2021 most people didn’t know what a booster was – now all we hear is boosters boosters boosters.

So why do we care so much about boosters right now? 

Let’s look at how we got here.

When we started to roll out the Covid-19 vaccine in early 2021, we had the clinical trials data from each of the companies that guided us on timing of shots and number of shots. 

We knew that following this regime would provide significant protection against getting infected with the virus and even better protection against severe illness and death. 

Most of the vaccines we have taken in our lifetime have required two or more doses plus boosters so this has been no different. We wondered as the Alpha variant took hold in early 2021 as we rolled out the vaccines and were relieved that data showed that protection against infection, severe illness and death was still very high. 

Just as we were reaching a high level of vaccination in Ireland, topping the league tables around the world,  and starting to open up, the Delta variant struck and we wondered once more. Thankfully the vaccines stood firm but we did see evidence that the Pfizer and Moderna vaccines provided a higher level of protection than Astrazeneca and Janseen vaccines against this Delta variant. 

The next data that turned up wasn’t surprising to those that understood the immune system but was difficult for the general public to understand. 

The immunity from the vaccines was waning after four or five months and we didn’t have as much protection as we did after the second dose of our vaccine. This normally happens after all vaccines. The initial antibody levels are high and they decrease over time.

For most viruses this waning immunity might not matter too much, mostly because you are rarely exposed to the virus as community levels are low. When was the last time you were exposed to measles or rubella? But given the case numbers and community transmission of Delta in the winter months our exposure to Covid-19 had never been higher. Breakthrough infections were on the rise here and case numbers climbed. 

Data then quickly emerged that the solution was to boost immunity with a third shot of vaccine and booster became the topic of conversation all over the world.

Israel had led the way and boosted their way out of a Delta surge and proved to the world that boosters worked. Other countries followed suit and we began boosting in Ireland a few months ago and after a slow start have eventually ramped up. This has been predominantly driven by the arrival of yet another variant. 

Three weeks ago, Omicron came on the scene and with increased transmissibility as a key characteristic, has spread rapidly throughout the world. The difference with this variant is that it’s much more highly mutated than the ones that came before it. Along with its increased ability to transmit, it’s better at evading vaccines too.

Just what we didn’t need as we were on the road to boosting our way out of the winter Delta surge. After an anxious wait of just over a week, data demonstrated that Omicron was indeed vaccine evasive and two doses would only give us about 30% protection against infection but some better protection against severe illness and death. 

This was as low as 13% with the single shot Janseen vaccine. Thankfully, the data also showed that the booster boosted this up to 70-75% and we all breathed a sigh of relief.  

As data emerged from other countries showing Omicron to be more transmissible than any other variant and the numbers from over the water in the UK started to rocket, all hands to the wheel was the mantra for the boosted booster programme here in Ireland. 

So the big question is whether the boosters will solve the problem of Omicron acceleration as it becomes ever more present here with each passing day. 

The Health Protection Surveillance Centre said it estimates that approximately 35% of reported cases are now the Omicron variant. It will no doubt be dominant before Christmas Day.While the boosters will provide significant protection against severe illness and deaths, the protection is less against infection with Omicron. This super transmissible Omicron will take full advantage of that gap in protection and breakthrough infections will accelerate fast.

We also won’t have time to get everyone boosted before Omicron takes off and it will take advantage of that too. We are hopeful that this variant may cause milder illness which may translate into less incidence of hospitalisation and ICU admissions, but the sheer volume of potential cases might make this completely irrelevant and we may see hospitalisations and ICUs climb regardless of it being milder.

A small percentage of a big number is still a big number. We also don’t have definitive information about what infection looks like across a range of age cohorts and across different vaccine status, so there’s still a lot we don’t know.

But we do know is that Ireland will not be any different to any other country in terms of surging case numbers – we’ve been the same as the rest in the previous fourth waves, this time won’t be any different.

The most we can do is manage the impact. The booster programme will no doubt provide the best defence in minimising the impact of that surge on both our people as well as our healthcare system, but it is still a race against time.

I think we’ve been in this race before, but this time our opponent is faster.

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Professor Christine Loscher
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