Almost everyone in the world, from young children to the elderly, is looking forward to the announcement of the first vaccine for the coronavirus becoming widely available to the public. We are all waiting to return to our regular pre-pandemic lives, and a vaccine sounds like the only miracle solution to this significant problem. It is obvious that having a proven effective vaccine will help; however, it may not magically solve everything, as recent data and studies suggest.
As of the end of July, there are around 140 vaccine trials in the early stages and 10 trials in different clinical phases. The initial data from the 10 clinical-phase candidates suggests that the first patients taking part in trials have produced antibodies that would neutralize the virus. In a U.S.-based study, phase three clinical studies have started and around 30,000 volunteers are expected to take part in the testing of a coronavirus vaccine in the upcoming months. According to well-known epidemiologists and vaccine researchers, the first publicly available vaccine may be ready as early as October 2020.
As almost everything in our daily lives has stopped and we desperately need a new solution to restart, public health experts are planning effective ways to disseminate and administer a vaccine to society. Who will be vaccinated first? How will the extensive costs be covered? What will be the reaction of anti-vaccine lobbyists? All these questions remain to be answered before we have the vaccine ready, and the more these are discussed, the more problems seem to appear for the uncertain post-vaccine period.
When measuring the quality of a vaccine for a specific disease or infectious agent, we generally measure it with two main indicators: effectiveness and efficacy. The efficacy of a vaccine is the percentage of reduction in disease incidence in a vaccinated group, compared with an unvaccinated group, in most of the cases in clinical trials. Effectiveness, however, is the ability of the vaccine to prevent outcomes of interest in the "real world." Therefore, when measuring how "good" a vaccine is or how protective it will be, we need to see its effectiveness and efficacy.
Recent data from the U.S. suggests the world needs the coronavirus vaccine’s effectiveness to be higher than 70% or even 80% before anyone can safely stop relying on social distancing measures and return to the previous normal. As an example, the measles vaccine has an effectiveness of 97% and the flu vaccine between 20%-60%. Efficacy means, for example, that if 10 people who haven’t been exposed to the virus are given a vaccine, that has an efficacy of 70%, that means that seven of them on average would not get infected.
Model research
Also, to understand what percentage of the world needs to be vaccinated and what the minimum efficacy of a vaccine is to claim it is safe, a group of researchers from the City University of the New York Graduate School of Public Health and Health Policy, working with scientists from the National School of Tropical Medicine at the Baylor College of Medicine, developed a computer simulation model of the entire U.S. population interacting with each other. Thanks to this model they were able to simulate different levels of the population being infected, vaccinated and/or hospitalized, just like a real-world scenario.
Depending on this model’s theory, if we were at the very beginning of the pandemic with nobody infected, we would be able to say the efficacy of the vaccine should be at least 60% to stop the spread of the virus. But due to different people with specific health conditions and people who refuse to get vaccinated, that has become an impossible scenario. Therefore, we would need vaccines that have an efficacy of above 60% even if the coverage would be close to 100%. If approximately 75% of the population gets vaccinated, then the efficacy would have to be at least 70%; if only 60% of the population gets vaccinated, the required efficacy rate rises to at least 80%.
However, these scenarios depend on the caveat that nobody is already infected. Recent data suggests 1% of Americans are immune to the coronavirus, from data gathered from random street tests, while the real number is thought to be much higher. The efficacy was supposed to be at least 80%, even in the previous scenario, so now that leaves us with a considerable task of finding vaccines that are very highly effective. We need to come up with something much more effective than the yearly influenza vaccine, for instance. Considering that the percentage of people globally infected with the coronavirus is increasing daily, it is also crucial to develop and start administering a vaccine as soon as possible. The later it becomes available, the higher the effectiveness rate of the vaccine needs to be, which starts to become an impossible task after a certain point.
A problematic scenario
Another problem we will encounter after the development of a vaccine is to see what will happen in the scenario where some people can’t or won’t get vaccinated. In a scenario where at least 75% of people globally need to be vaccinated to stop physical distancing measures, also called "herd immunity," we will have an even greater issue if more than 25% of the world population refuses to be vaccinated for different reasons. Anti-vaccine campaigns seem to be gaining popularity globally in recent years, leaving a big burden of diseases on countries that had previously eliminated such illnesses, including polio and measles.
Some people will also have different health conditions which will prevent them from being vaccinated. Therefore, this is a hugely important issue already for the selection and application of a vaccine, after we have it ready. Will it be mandatory for all healthy people, and what will happen if an insufficient percentage of the population agrees to be vaccinated?
Finally, a major issue is the type of virus we are trying to fight. Coronaviruses are a type of RNA virus, and RNA viruses have high mutation rates, up to a million times higher than their hosts. These high rates are correlated with enhanced virulence and evolvability. Assuming we come up with a vaccine this year for the coronavirus, there is no guarantee that we won’t have a novel version next year, which will require a new vaccine, similar to a new influenza vaccine being applied each year. In the best-case scenario, we will have vaccines updated yearly, with the current coronavirus strain, and that will require substantial global organization and planning to prevent any further lockdowns.
This has recently led public health experts and social scientists to start thinking that a vaccine would not be a magical solution to all of our problems. We would need more measures, perhaps also curative drugs, to achieve a zero-case fatality rate. It is, of course, going be a big step toward returning to our normal lives, if we come up with a vaccine with a high efficacy rate; however, we will still have to continue social distancing measures at least for the next few years. It is better if countries prepare for this reality and plan for the worst-case scenario, while also hoping for the best.
*Public health expert and board member of the Partnership for Maternal, Newborn and Child Health (PMNCH)