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Smallpox was one of the world’s most feared diseases and had a mortality rate of 30 percent. It had existed for 3,000 years, but was eventually eradicated by a collaborative global vaccination programme, led by the World Health Organisation. The last known natural case was in Somalia in 1977.
Larry Brilliant, CEO of Pandefense Advisory, who led the WHO’s smallpox eradication programme, told The Guardian: “It will be harder to get rid of Covid than smallpox.”
One of the major challenges for vaccine developers is the fact coronaviruses do not tend to trigger long-lasting immunity.
Almost one quarter of common colds are caused by human coronaviruses, but the immune response fades so quickly that people often become re-infected the next year.
Scientists at Oxford University have discovered that the immune system’s response to SARS-COV-2 – the virus that causes COVID-19 – follows a similar pattern.
The researchers analysed blood from patients who had recovered from the disease and found that the number of IgG antibodies, responsible for longer-lasting immunity, initially rose steeply before decreasing again.
This suggests that vaccine developers may struggle to produce a vaccine that generates persistent, high levels of antibodies to wipe out the virus and also “T” cells to destroy infected cells.
Stanley Perlman, a veteran coronavirus researcher at the University of Iowa, said: “If the natural infection doesn’t give you that much immunity except when it’s a severe infection, what will a vaccine do?
“It could be better, but we don’t know.”
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Another potential difficulty revolves around the rate at which the virus evolves through mutation.
Although SARS-COV-2 appears relatively stable, mutations are inevitably occurring, in particular the so-called protein spike that enables the virus to invade human cells.
Most of the coronavirus vaccines under development are targeting this spike.
If it mutates too much, then antibodies produced by the vaccine will be out of date and will not prevent infection.
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Martin Hibberd, professor of emerging infectious diseases at the London School of Hygiene and Tropical Medicine, who helped identify some of the virus’s mutations, called them “an early warning”.
Currently there are reported to be around 100 experimental vaccines under development.
Two of the most promising are from US biotech firm Moderna and Oxford University.
The Moderna prototype vaccine produced antibody levels similar to those found in recovered patients in 25 people who were injected with their vaccine.
The Oxford University vaccine was initially tested on rhesus macaque monkeys, but did not stop them contracting the virus.
However, it did appear to prevent the monkeys from developing the lethal pneumonia, that kills so many COVID-19 patients.
If humans react the same way, vaccinated people would still spread the virus, but be less likely to die from it.
The overriding likelihood is that any potential vaccine will only provide partial protection, meaning that the virus will never be eradicated and that human society will have to adjust to living with it.
That means governments will have to extensively monitor for infections and implement periodic lockdowns to contain the virus’s spread.
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