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2020 was the year of the covid lockdown, 2021 was the year of the vaccine and 2022 was the year of the global restart. 2023 will be the predicted year of the variant. The first Covid strains of concern—from alpha in the UK to beta in South Africa—muddy the picture of where the pandemic will go next. Alpha was naturally better at transmitting, while beta was able to evade pre-existing immunity to some extent. What would the long-term pattern of evolution look like?
In 2022 the picture became clearer, with the Omicron BA.1 variant causing a major epidemic. This led to an accumulation of immunity in the population, followed by a decline in transmission, only for a new subvariant, BA.2, to emerge against which this immunity was less effective. A major pandemic followed and the cycle began again, with another cycle beginning in mid-2022 when BA.5 came out.
If this evolutionary path continues, we will see this cyclical pattern in 2023 and beyond. It’s the same dynamic as seasonal coronaviruses that have caused epidemics for decades. A 2021 study by researchers at the Fred Hutchinson Cancer Research Center found that the coronavirus evolves slowly over time, so earlier immunity is less effective.
This will pose a challenge to the Covid-19 vaccination campaign; If the virus evolves this way, we would ideally update the vaccines, so the viral proteins in the vaccine are a close match to the variants found in our bodies circulating. But updating vaccines takes time. For influenza, the World Health Organization makes recommendations twice a year on which strains should be in that season’s vaccine in each hemisphere. Because of production and distribution timelines, decisions about winter vaccines are made more than six months in advance. That makes vaccine selection a prediction problem.
When it comes to selecting influenza vaccines, the teams use a range of data, from the rate of development of circulating variants in genomic data to tests of their immunogenic properties. An additional complication is the variability in what different populations have previously been exposed to. Some countries may have more existing immunity than others, and so variants that can evade this immunity have a greater advantage. We often see different influenza viruses predominating in different continents and countries.
In 2023, this prediction challenge will become routine even for Covid. Some countries have already approved shots that are compatible with the Omicron BA.1 subvariant. But how well will these new vaccines match up to the variants that are circulating down the line? Decisions for the 2023-24 Northern Hemisphere winter will have to be made in early 2023. Making the right choices can have a big impact on the size and intensity of future Covid waves. For the H3N2 influenza subtype, which causes the largest seasonal epidemics, challenges surrounding vaccine selection and production mean that efficacy against symptomatic disease is typically less than 50 percent.
In the future, there is hope for progress on “universal” coronavirus vaccines, which will be highly effective against different types. But the history of the development of other universal vaccines, such as influenza, suggests that complete success is far from guaranteed. As a result, the coming year will be the start of a long cat-and-mouse game, updating vaccines against evolving viruses. Resolving this predictive question—and developing the resulting vaccines—will be one of the major health challenges of 2023.
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