As pharmaceutical companies race to bring a coronavirus vaccine to market, some epidemiologists think the efficacy of the vaccine should be higher than the 50% standard set by the Food and Drug Administration.
Efficacy is simply the rate at which a vaccine will either prevent people from contracting the virus or reduce the symptoms associated with the virus.
A vaccine is necessary for speeding up the process of achieving herd immunity, which occurs when a large portion of the population, the “herd,” becomes immune to a virus. The higher the efficacy rate, the quicker herd immunity is achieved. What makes a 50% efficacy potentially problematic is that there are significant hurdles to getting enough of the population vaccinated.
“If this were Ebola, for instance, I could see how that might be sized at 50%,” said George Rutherford, a professor of epidemiology and biostatistics and director of the Prevention and Public Health Group at the University of California, San Francisco. “But [the coronavirus] is so widespread, you might want a little bit more.”
Yet even 50% could yield a substantial benefit.
“I think a lot of folks were disappointed because 50% is a relatively low target,” said Jennifer Reich, a sociologist at the University of Colorado, Denver and author of the book Calling the Shots: Why Parents Reject Vaccines. “Of course, when we’ve seen almost 200,000 deaths in less than six months, we can say that even lowering death by 50% would be a significant improvement to the healthcare system.”
Some vaccines have lower rates of efficacy, like the annual flu vaccine, which usually has an efficacy of 40%-60%. Others are much higher, such as the shingles vaccine, at 91%-97%, and measles vaccine, at 93%-97%.
One hurdle facing mass vaccination is that the vaccine will likely require two doses, each a month apart, which will make the job of inoculating the public more difficult.
“The first dose primes the immune system,” said Dr. William Schaffner, a professor of preventive medicine and infectious diseases at the Vanderbilt University Medical Center. “The second dose, a month later, gives it an additional push. You get much higher protection levels and you can anticipate that … they will last for a longer time. It’s the second dose that really assures the effectiveness.”
Not everyone will follow up with the second dose.
Another problem is that once the vaccine arrives, there will be some who throw caution to the wind.
“It is already clear that the population thinks, figuratively speaking, that two days after the vaccine is announced everybody can throw their masks into the trash can and go back to attending your local high school basketball game. … They’re going to be surprised when the public health community says, ‘No, keep the masks. Keep up the social distancing. You’re going to need that for a long time,’” said Schaffner.
Finally, a significant portion of the public may refuse to be vaccinated.
A recent Suffolk University poll found that two-thirds of respondents would think twice before getting a coronavirus vaccine, and 44% said they would wait for others to try it first. More than 1 in 5, 23%, said they would not take the vaccine.
There are multiple reasons why people refuse to take a vaccine, including a semieffective anti-vaccine campaign that received the support of some celebrities and a distrust of this particular vaccine based on the shortened FDA approval process.
But Reich explains that there is also a more fundamental reason.
“The challenge with vaccines is that we are asking healthy people who are not sick to take on the risks [of side effects]. That’s really different than other medications that treat conditions and that makes the expectation for safety higher,” said Reich.
Often, the side effects of a vaccine are redness and swelling around the injection site or fatigue. But sometimes, the side effects are more serious.
On Tuesday AstraZeneca and the University of Oxford suspended phase three of the clinical trial of their coronavirus vaccine after a participant in the United Kingdom experienced serious adverse health conditions. National Institutes of Health Director Francis Collins said the problem that led to the pause in the trial is a rare affliction known as transverse myelitis, a neurological disorder that causes inflammation of the spinal cord. It has not been confirmed whether the condition was a result of the vaccine.
