Most experts agree that the only thing which will put the current Covid-19 pandemic to rest is some kind of vaccine.  One firm — Pfizer/BioNtech — has progressed to what is called a Phase 3 trial, which involved about 43,000 people who took it with apparently no serious side effects.  There is still a long way to go even with the most advanced projects, because achieving “herd immunity” — enough immune people to discourage the virus from spreading — may require on the order of several billion doses.  And many of the prospective vaccines require two injections spaced weeks apart, which further complicates matters.

Engineers are familiar with trade-offs that are usually imposed by economic restrictions.  When I was a young engineer just out of college, I was teamed with an older and more experienced engineer, and one day we were talking about various possible ways to tackle a certain problem in a new design we were working on.  I described three or four different ways to tackle it that I thought were pretty clever, but he seemed unimpressed.  Finally, I asked him why he wasn’t more excited about these innovative ideas I was proposing.

“Heck,” he said, “I can build one of anything!  The real challenge is making thousands of them work at a price we can afford.”  

The harsh realities of the marketplace had educated him to look not just for technically sweet ideas, but for ideas — new, old, or otherwise — that would do the best job for the least money.  That taught me that having clever ideas — or one dose of a highly effective vaccine — is only a small step toward solving a real-world engineering or technical problem.

Making a billion high-quality vaccine doses in a short time is a challenge that hasn’t been discussed much so far.  But supposing that vast production problem is overcome, and reliable vaccine doses begin to enter the pipeline, who is going to get them first

An interesting study cited by a recent BBC article says that the first doses should go to different groups, depending on how effective the vaccine is.  No vaccine is 100 percent effective, and this is especially true of virus vaccines.  The annual flu-virus vaccine that millions of people get is rarely more than 60 percent or so effective, depending on the particular year and the mix of viruses that show up after the vaccine is developed. 

There are different ways to measure the effectiveness of vaccines.  One way is to measure how many people who are vaccinated and then exposed to the virus develop symptoms.  Another way is to measure how likely a vaccinated and exposed person is to spread the disease to others, whether or not they manifest symptoms.  The study’s authors point out that if you developed a vaccine that was only 30 percent effective in preventing symptoms, it would fall below the US Food and Drug Administration’s 50 percent threshold and wouldn’t even be approved.  But if it happened to be 70 percent effective at stopping people from spreading the virus, it would actually do more good than a different vaccine that prevented symptoms with 100 percent effectiveness but allowed the virus to spread.

That is why there is no single answer to the question: “Who should get the vaccine first?”  If it is most effective in preventing the virus from spreading, then the target population should be the ones who spread it the most.  Currently that appears to be older children and younger adults, say between 10 and 35.  Few people in that group die of the virus, but just because many of them have either mild symptoms or are asymptomatic, they spread it very easily. 

On the other hand, if the vaccine is good at preventing symptoms but not so good at stopping the spread, you probably want to target the population that is most vulnerable to the disease:  people in rest homes and over 65.  That will save the most lives in the short term, while giving us time to vaccinate the rest of the population to approach the goal of herd immunity.

Any way you slice it, we face a very long uphill battle in fighting this disease.  In some countries such as the US and China, the expense of buying and distributing the vaccine is relatively trivial compared to other things the government is doing.  But in poorer countries, vaccinating the majority of the population with anything is a major challenge, and so we can expect the disease to hang around in pockets long after it has been controlled in more economically well-off places.  So the last thing to go may be travel restrictions concerning COVID-19, at least to some countries where it may not be controlled for several more years.

Within a given country, the distribution of the vaccine may be implemented mainly by the government, mainly by private enterprise, or more typically by a combination of the two.  As it is in the interests of every government to free its citizens from the threat of COVID-19, substantially free distribution would seem to be a no-brainer, although there are practical obstacles to that as well.  Certain minority populations have been disproportionally affected by COVID-19, and the US National Academies of Science, Engineering, and Medicine has stated that there is a “moral imperative” to make sure that this imbalance is addressed in any proposed distribution scheme. 

And last but not least, there is the problem that not everybody is going to want to be vaccinated.  We are a long way from the 1950s, when Jonas Salk was universally praised as a god-like hero and millions of US citizens gratefully took their children to receive polio vaccine injections without raising even a quibble concerning its safety.  Nowadays, the pronouncements of experts always inspire somebody on the internet to say, “Sez who?” and the small but vocal opponents of any kind of vaccination have persuaded lots of people at least to hesitate before believing uncritically anything an expert says. 

Even with all these uncertainties, it does look like we get a vaccine sometime, and eventually it will begin to slow down the spread of COVID-19.  As far as I’m concerned, it can’t come too soon.

Karl D. Stephan received the B. S. in Engineering from the California Institute of Technology in 1976. Following a year of graduate study at Cornell, he received the Master of Engineering degree in 1977...