Coronavirus has seven known strains that infect humans, and many more that affect animals. Photo / 123RF
Coronavirus has seven known strains that infect humans, and many more that affect animals. Photo / 123RF
COMMENT:
The world is waiting breathlessly for a Covid vaccine. Countries are pouring billions into vaccine research, and many of the world's biggest biotech companies are busily at work. Already there are reports of over 60 new vaccines in pre-clinical testing, with a handful in human testing.
Most national pandemicplans centre around controlling community outbreaks until a vaccine is available. World leaders are publicly expressing their expectation for a vaccine within a year, while others like Anthony Fauci, head of the US National Institute of Allergy and Infectious Diseases, say it might take as long as two years.
But if we look at the history of coronavirus vaccines, things appear less sanguine. Coronavirus has seven known strains that infect humans, and many more that affect animals. Most cause respiratory problems.
Some strains cause bronchitis in chickens and others cause kennel cough in dogs. The poultry coronavirus problem alone is estimated to cost the world economy 8 billion dollars annually, yet the average person would probably never have heard of coronavirus before this year.
Yet we are all intimately familiar with human coronaviruses, even if we don't realise it. Ten percent of the colds we suffer are caused by coronaviruses. This family of viruses has been with us for a very long time.
In addition to the animal strains, and the four non-pandemic common cold coronavirus strains, the world has experienced two strains responsible for human pandemics: MERS, a disease transmitted by close contact with sick camels and ingestion of their milk and urine, and SARS, a disease that killed almost a thousand people, peaking in 2003 and then mysteriously disappearing from the world stage. And now we have a third pandemic coronavirus, identified just a few months ago: severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2, the virus that causes Covid-19.
There are several good reasons that an effective coronavirus vaccine has eluded us for the seventy years that we've known about coronaviruses, all the while costing us huge losses in productivity, money, and lives even before Covid came along.
One reason is that coronaviruses, like the influenza virus, are not very robust. They tend not to grow well in cell culture. So rather than growing quickly in massive 'farms' of purpose-bred cells, they require painstaking, slow, and expensive growth in live chicken eggs. Newer techniques using recombinant gene techniques can churn out numerous vaccine candidates much more quickly, but the results can be quite hit-and-miss. And all vaccines require expensive safety and efficacy testing in humans, because of the risk they might provoke an immune response so intense that it actually harms the patient.
Dr Gary Payinda. Photo / Supplied
Being simple, tiny single-strand RNA viruses, coronaviruses also have a tendency to mutate rather quickly, which means previous vaccines have been effective only against certain subtypes. For chicken farmers this has meant coronavirus vaccines that are expensive, yet only provide partial protection for their livestock. This is better than nothing, but not a magic bullet.
Another challenge vaccine makers face is that the immunity spurred by coronavirus vaccines is often short-lived. This isn't a problem for a farmed chicken with a two-year lifespan, but it's a serious issue for immunity over the span of a human lifetime.
The reason is coronaviruses are great at eluding our immune system. Even survivors of MERS, a disease which killed a third of its victims, showed immune responses that dropped precipitously after just two to three years. That compares poorly to a disease like measles, where infection (or two doses of the MMR vaccine) typically provides lifelong immunity.
One only has to look at the common cold to realise that despite repeated infection, we don't ever develop lasting or effective immunity.That bodes poorly for the world's great hope: a Covid vaccine that completely eliminates Covid, and lasts a lifetime.
Coronavirus family history suggests something more prosaic: a Covid vaccine that is only partially effective, and requires yearly boosters. In that respect, it would be similar to the flu vaccine. Still a lifesaver, still what I'd recommend to my at-risk patients...just not as effective as we might have wished.
I certainly hope this won't be the case with a future Covid vaccine. It is too early to know. But history suggests we may remain unpleasantly vulnerable to Covid even after a vaccine is discovered.
• Gary Payinda works as an emergency medicine and helicopter retrieval doctor in Northland and Auckland
