Original article (in Serbian) was published on 05/11/2021
Vaccinated people can get sick, and that is to be expected. Not only from Covid, but also from chickenpox, smallpox, polio and other infectious diseases for which vaccination is mandatory in most countries. No vaccine is 100% effective because specific immune systems are not able, even after vaccination, to generate an adequate response that would protect them during subsequent exposure to the infection. However, people with such an immune system are protected by the reduced transmission of the infection, which is achieved by vaccinating the vast majority of those whose immune systems can generate an adequate response to the infection.
Numerous studies have shown that Covid vaccines are effective and that their efficacy does not differ much from the efficacy of other infectious disease vaccines. Clinical studies consistently show that the efficacy of the Pfizer-BioNTech vaccine is about 95 percent when it comes to previous coronavirus strains. Similar data are obtained in Israel, a country with a high vaccination rate with this vaccine, where the vaccine’s effectiveness against the symptomatic form of infection caused by the delta strain is 88 percent. Very similar to this finding, it is registered in the UK that the Pfizer-BioNTech vaccine is 96 percent effective in the context of hospitalization as a result of delta strain infection. For comparison, after receiving the second dose of MMR vaccine, about 99 percent of people are immune to chickenpox. In contrast, the varicella vaccine is 85 percent to 90 percent effective in preventing all chickenpox infections and almost entirely effective in preventing severe consequences of infection.
Why do we have a far higher percentage of infected among vaccinated against Covid than against chickenpox or smallpox?
The answer is very simple: the transmission of the virus that causes chickenpox or smallpox is almost entirely stopped by the enormous scope of vaccination.
Those vaccinated against coronavirus do not get sick because the vaccine is ineffective but because there are not enough vaccinated people to stop the transmission of the virus.
When we say that the effectiveness of a vaccine is 90 percent, it means that people who have been vaccinated have a 90 percent lower risk of developing the disease after exposure to a certain virus than those who have not been vaccinated. This does not mean that we are protected from the virus 90 percent of the time, nor that 10 percent of those vaccinated will surely get sick. This actually means that 90 percent of those vaccinated will develop an adequate response in the conditions of exposure to the infection, i.e., that they will not become infected, that they will develop an asymptomatic form of the infection or that they will have a mild clinical condition.
On the other hand, 10 percent of people have immunity that after vaccination will not develop an adequate response to exposure to infection, and in conditions of exposure to infection will be as likely to become infected or develop a more severe condition than unvaccinated. As mentioned earlier, the only way to protect these people from infection is to reduce the transmission of the infection, which is achieved by vaccinating those whose immune system creates an adequate response to the infection.
What happens if the vaccination coverage decreases?
When vaccination against some infectious diseases is mandatory, as is the case with whooping cough or diphtheria, one gets the impression that these diseases have been completely eradicated and are part of some ancient times. However, experiences of countries in which anti-vaccine movements against these vaccines have strengthened in some periods suggest that we would probably relive a pandemic of these seemingly archaic infectious diseases if we stopped the vaccination process.
In Japan, the rate of those vaccinated against whooping cough was over 70 percent in 1974, and 393 new cases of the infection were registered that year, while there were no deaths. Five years later, with the strengthening of the anti-vaccine movement, and the reduction of the number of vaccinated, 13,000 infected people were registered, and 41 people died.
A similar thing happened in the countries of the former Soviet Union during the 1990s. While in 1989, there were only 839 cases of diphtheria and no deaths, in the early 1990s, the low immunization rate for children and the lack of additional vaccines for adults led to 50,000 infections and over 1,700 deaths due to diphtheria. Among these people was a certain percentage of vaccinated, those whose immune system is unable to develop an adequate response to infection with these viruses, and who were endangered by increased transmission of the infection caused by the decision of a certain percentage of people not to be vaccinated with highly tested vaccines.
Why is there a higher percentage of vaccinated than unvaccinated among the infected in some countries?
In pandemic conditions, when vaccination is not mandatory, and countries differ in the scope of vaccination, it is very likely that at some point, there will be an increase in doubts about the effectiveness of the vaccine. If the percentage of vaccinated is not large enough to stop or greatly reduce the transmission of the infection, among those infected, as expected, for the aforementioned reasons, there will be both unvaccinated and vaccinated.
If the public develops expectations that the vaccine protects 100 percent of the infection and that – if we are vaccinated – we can’t get sick, then citizens will become skeptical about vaccination in conditions where vaccinated people around them are getting sick. Apart from the fact that vaccinated people will have an asymptomatic form of infection or a mild clinical condition, which is certainly an adequate response of the organism to exposure to infection, for a certain percentage of those whose immune system is unable to develop an adequate response to infection, the exposure to the virus will produce the same consequences as in those who have not been vaccinated.
With the increase of vaccinated people in a country, our perception grows that more and more vaccinated people around us are infected. And that is to be expected, because the higher the percentage of vaccinated in a country, the more it is expected that there will be more vaccinated among those infected.
Imagine a hypothetical situation that in conditions where the vaccine is 90 percent effective, the chance that the vaccinated will be hospitalized due to infection with a specific virus is reduced from 1 percent to 0.1 percent.
If 900,000 people are vaccinated in a population of one million people, 900 people are expected to be hospitalized due to the virus infection (0.1 percent). On the other hand, out of the remaining 100,000 unvaccinated, 1,000 will be hospitalized (1 percent). In such circumstances, we will get the impression that every other hospitalized person has been vaccinated and that the vaccine is at the same time very effective. Unfortunately, in these conditions, it is very likely that due to subjective biases in the interpretations of such experiences, there will be an increase in skepticism towards vaccination among citizens.
The only way both unvaccinated and vaccinated people can be protected is to have the vaccination coverage large enough to stop the transmission of the infection. With non-vaccination, we endanger not only ourselves and other unvaccinated people, but also a certain percentage of vaccinated whose immune system is not able to develop an adequate reaction to exposure to the virus, and who cannot have any other protection from the virus than vaccinating as many of us as possible.