Do COVID-19 vaccines need to be changed regularly?

Flu vaccines need to be evaluated annually to make sure they are effective against new flu viruses. Will the same apply to COVID-19 vaccines? To determine whether and to what extent it may be necessary, a team of researchers from Charité – Universitätsmedizin Berlin compared the evolution of ‘common cold’ endemic coronaviruses with influenza viruses. . The researchers conclude that, as the pandemic progresses, vaccines need regular updating. A few years into the period after a pandemic, however, vaccines are likely to last longer. This study was published in Virus death*.

Influenza viruses have been masters of the human immune system. They go through changes as soon as antibodies made by the immune system in response to a previous infection or vaccine cannot be neutralized. That is why the complex task of evaluating and updating the flu vaccine needs to be repeated every year. Variables within SARS-CoV-2 have already yielded a number of modifications, some of which (like the South African variant) partially suppress the body’s immune response. As a result, some vaccine manufacturers have begun to develop new versions of their vaccines. What does this mean for the future? Will COVID-19 vaccines mirror flu vaccines in need of regular updating?

To determine whether, over the long term, SARS-CoV-2 tends to exhibit a protective clearance equivalent to that of influenza viruses, Charité anthropologists have studied evolution the genetics of the four currently known ‘common cold’ coronaviruses. These relatively harmless coronaviruses are known to be responsible for about 10 percent of the world’s common cold and have been circulating in humans for much longer than SARS-CoV-2. Just like SARS-CoV-2, they enter human cells using the ‘spike protein’, a surface protein that gives the virus a crown-like appearance (and name). The spike protein is also a target for all conventional COVID-19 vaccines.

For their study, the researchers focused on the two most well-known coronaviruses (known as 229E and OC43), detecting changes in the spike gene around 40 years in the past. The researchers began by comparing sequences from a range of old samples deposited in a genetic order data bank. Based on the mutations that had emerged over time, they made phylogenetic trees both for coronaviruses. The researchers compared their findings with the phylogenetic strain of H3N2, a subtype of influenza that is particularly effective in suppressing the human immune response.

The researchers’ calculations revealed one feature common to phylogenetic recurrence of both the coronaviruses and the influenza virus: all three had a ladder-like shape. “An irregular tree of this type is the result of the replacement of one circulating virus variable by another that had a fitness benefit,” explained the first author in the study, Drs. Wendy K. Jó from the Charité Institute of Virology. “This is evidence of an ‘antigenic drift’, an ongoing process in which changes in surface structures allow viruses to evade the human immune response. It causes these endemic coronaviruses to escape the infection. immune system, just like the influenza virus. However, one also needs to look at the rate at which this evolutionary change is taking place. “

For this step, the researchers determined the evolutionary stages of the three viruses. While the influenza virus accumulated 25 mutations per 10,000 nucleotides (genetic building blocks) each year, the coronaviruses accumulated approximately 6 such mutations in the same period. The rate of change of endemic coronaviruses was therefore four times slower than that of influenza virus. “Regarding SARS-CoV-2, this is good news,” summarizes Prof. Dr. Christian Drosten, Director of the Institute of Virology and researcher at the German Disease Research Center (DZIF).

SARS-CoV-2 is currently estimated to change at a rate of about 10 mutations per 10,000 nucleotides per year, resulting in its rate of growth being significantly higher than that of endemic coronaviruses. “This rapid genetic mutation in SARS-CoV-2 is evident when a number of viral changes have emerged across the globe,” explains study director Dr. Dr. Jan Felix Drexler, researcher at both the Institute of Virology and the DZIF. “However, this is likely due to the high levels of infections seen during the pandemic. When infection numbers are so high, a virus will be able to develop more quickly. the evolutionary levels seen in the common endemic cold coronaviruses, we expect SARS-CoV-2 to begin to change more slowly once diseases die – meaning once ‘ s that a large proportion of the world’s population has developed immunity either as a result of infection or through vaccination, so we expect that COVID-19 vaccines need to be monitored regularly throughout the pandemic. and updating where necessary. Once the situation has settled, effective vaccines are likely to last longer. “

* Jo WK et al. Evolutionary dynamics of endemic human coronaviruses. Vir Evol 2021. doi: 10.1093 / ve / veab020

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