RE: Enjoy Summer....7 Jun 2021 13:00
From New Scientist article 15th May:
Another factor to weigh up in relation to variants is an immunological phenomenon called original antigenic sin.
This is where an updated vaccine reactivates an earlier immune memory rather than creating a new one. It has been seen with other viral infections including flu, says Anthony Costello at UCL, but whether it will be a problem with the virus that causes covid-19, SARS-CoV-2, remains to be seen. Studies to establish this are urgently needed, says John Moore at Weill Cornell Medicine in New York, because original antigenic sin could render a variant-specific booster campaign pointless.
Booster shots could fail for other reasons. A third dose of viral vector vaccines like the Oxford/AstraZeneca one could just boost the immune response to the harmless virusused as a vehicle to deliver the active ingredient. “One of the concerns is that we may not be able to augment the antibodies against the [SARS-CoV-2] spike protein,” says Teresa Lambe at the University of Oxford, who worked on the vaccine’s development. She is doing experiments to determine the immune response to a third dose.
For this reason and others, it may be preferable to boost people’s immunity with a different vaccine from the one
they got the first two times. There is some evidence that using different vaccines for the first and second dose – a method called heterologous prime-boost vaccination– produces a stronger immune response than using the same vaccine for both. Russia’s Sputnik V, for example, is a heterologous prime-boost vaccine and the latest real-world figures from the country show that it is 97.6 per cent effective, which would make it the most effective covid-19 vaccine in the world.
Ongoing experiments in the UK are examining the effects of mixing and matching first and second vaccine doses, and the results could inform decisions on a booster campaign, says Harnden. All of these uncertainties emphasise an important point that has been largely forgotten amid vaccine euphoria, says Costello. “The idea that you can continually boost [immunity] is both logistically difficult and may be immunologically difficult.” We may face breakthrough infections that can’t be vaccinated against and so we will still need interventions such as masks, ventilation and social distancing. “Vaccination has been great, but it’s not going to solve the problem in its entirety,” says Costello.
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