Why a COVID Vaccine is Unlikely

Posted by Ed 13 days ago
It would be hard to overstate the importance of developing a vaccine to Sars-CoV-2 – it’s seen as the fast track to a return to normal life. That’s why the health secretary, Matt Hancock, said the UK was “throwing everything at it”.

But while trials have been launched and manufacturing deals already signed – Oxford University is now recruiting 10,000 volunteers for the next phase of its research – ministers and their advisers have become noticeably more cautious in recent days.

This is why.
Earlier this week, England’s deputy chief medical officer Jonathan Van-Tam said the words nobody wanted to hear: “We can’t be sure we will get a vaccine.”
But he was right to be circumspect.
Vaccines are simple in principle but complex in practice. The ideal vaccine protects against infection, prevents its spread, and does so safely. But none of this is easily achieved, as vaccine timelines show.
More than 30 years after scientists isolated HIV, the virus that causes Aids, we have no vaccine. The dengue fever virus was identified in 1943, but the first vaccine was approved only last year, and even then amid concerns it made the infection worse in some people. The fastest vaccine ever developed was for mumps. It took four years.
Scientists have worked on coronavirus vaccines before, so are not starting from scratch. Two coronaviruses have caused lethal outbreaks before, namely Sars and Mers, and vaccine research went ahead for both. But none have been licensed, partly because Sars fizzled out and Mers is regional to the Middle East.
The lessons learned will help scientists create a vaccine for Sars-CoV-2, but there is still an awful lot to learn about the virus.
A chief concern is that coronaviruses do not tend to trigger long-lasting immunity. About a quarter of common colds are caused by human coronaviruses, but the immune response fades so rapidly that people can become reinfected the next year.
Researchers at Oxford University recently analysed blood from recovered Covid-19 patients and found that levels of IgG antibodies – those responsible for longer-lasting immunity – rose steeply in the first month of infection but then began to fall again.

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Ed 13 days ago
Why are vaccines against many human viral diseases still unavailable; an historic perspective?
The number of new and improved human viral vaccines licensed in recent years contrasts sharply with what could be termed the golden era (1955‐1990) when vaccines against polio‐, measles, mumps, rubella, and hepatitis B viruses first became available.
Here, we attempt to explain why vaccines, mainly against viruses other than human immunodeficiency virus and hepatitis C virus, are still unavailable.
They include human herpesviruses other than varicella‐zoster virus, respiratory syncytial and most other respiratory, enteric and arthropod‐borne viruses. Improved oral poliovirus vaccines are also urgently required. Their unavailability is attributable to regulatory/economic factors and the properties of individual viruses, but also to an absence of relevant animal models and ethical problems for the conduct of clinical of trials in pediatric and other critical populations.
All are portents of likely difficulties for the licensing of effective vaccines against emerging pathogens, such as avian influenza, Ebola, and Zika viruses.
Over the past 40 years the rate of development of newly licensed human viral vaccines, compared with veterinary vaccines, has been disappointingly slow. Viral vaccines licensed for human immunization and distribution in the United States and other countries in 2019  are mainly used for the prevention of pediatric diseases.  
Despite much early optimism throughout the 1980s, benefits from the use of molecular recombinant DNA (rDNA) technologies in human viral vaccine development were perceived in 1991 to be underwhelming.1
The single exception was the then recently approved HBV vaccine, prepared from virus‐like particles (VLPs) after expression in yeast. Fast‐forward to 2019, traditional approaches have, in the meantime, resulted in several new and improved vaccines.
However, after 28 years, human papillomavirus (HPV) vaccines, also prepared as VLPs in yeast, 2 and an influenza vaccine consisting of baculovirus‐expressed hemagglutinin (Flublok)3 are the only other examples of newly licensed human vaccines that were developed entirely by the use of rDNA technologies 
Reasons, why vaccines against human immunodeficiency viruses (HIV) are unavailable, are complex and have been comprehensively dealt with elsewhere.8 However, despite monumental efforts over 30 years, vaccines for the prevention and/or prophylaxis of infection by HIV still appear to be some years away.

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