Vaccination an opportunity for collective immunity

Vaccination an opportunity for collective immunity

Immunizations are by far the most effective tool against infectious diseases. They protect us from many infectious diseases; with their help, the scourge of humanity, smallpox, was eliminated. Even before the coronavirus epidemic, about one billion doses of vaccines were administered worldwide every year, saving nearly 2.5 million people from death̨.

Experts estimatę that some 122 million people owe their lives to vaccines, without which they would not have had a chance to survivé even childhood.

The COVID-19 vaccine is an opportunity to immunize the public against SARS-CoV-2 virus infection. The vaccine triggers the natural production of antibodies in the human body. It stimulates our immune cells so that they protect us from infection.

Types of vaccines against COVID-19

Research on a vaccine against COVID-19 began in January 2020, as soon as the genetic sequence of the SARS-CoV-2 coronavirus was published. A huge motivation for the work was both the health and economic impact of the COVID-19 pandemic. As a result, the first vaccine prototypes were ready to begin human clinical trials as early as mid-March 2020.

So far, two vaccines produced with mRNA technology (from BioNTech/Pfizer and Moderna) and two vector vaccines (from AstraZeneca and Janssen Pharmaceutica, part of Johnson & Johnson) are approved for marketing in European Union countries.

The mRNA is a synthetic vaccine that contains no virus, only a short fragment of RNA in which is encoded the “command” to synthesize in the cells of the vaccinated person the S (spike) protein of the SARS-CoV-2 virus, which, being a potent antigen, stimulates the body’s immune response. The production of this vaccine does not require working with the infectious virus, growing it and weakening its virulence, which greatly simplifies and speeds up the production of the vaccine. For example, it takes about six months to produce a classic flu vaccine, while an mRNA vaccine takes about a week, which is of great importance during an epidemic. For many years, mRNA technology has been used in the development of vaccines, such as those against Zika, influenza, rabies, and malaria, as well as in the development of cancer vaccines.

Vector vaccines do not contain coronavirus, but use a human-inert other virus, from whose RNA the genetic material that allows multiplication has been cut out, and in its place has been inserted an RNA fragment of the SARS-CoV-2 coronavirus responsible for the production of protein S by the cells of the vaccinated person. The vector vaccines were developed using technology that has been used in HIV and Ebola virus research, among others.

All vaccines, before being approved for widespread use, must undergo strictly supervised clinical trials. The results of these studies are analyzed by the relevant review bodies. In the European Union, such a role is played by the European Medicines Agency (EMA).

It is worth remembering that no preparation completely protects against the disease. For now, it is known that vaccination protects against a severe course of COVID-19.

New variants of the virus vs. vaccines

The goal of a parasite such as a virus is survival. The virus uses the resources of its “host” to reproduce and transmit to subsequent hosts. “Smartest” viruses do not kill their hosts, but live in their bodies for many years, becoming active, for example, during times of reduced immunity.

Mutations of viruses are natural stages in their development. The SARS-CoV-2 coronavirus is also evolving to become more contagious but less lethal. RNA viruses, of which it is one, generally mutate quite rapidly, and since SARS-CoV-2 is one of the largest known RNA viruses, it has a high mutation rate.

Mutations of the virus are created as it multiplies (replicates) in the cells of subsequent infected individuals (i.e., hosts). Therefore, vaccination not only reduces the risk of COVID-19 disease and severity, but also slows the formation of subsequent mutations.

New mutations of the virus so far do not cause us to need new vaccines. Studies have shown that current vaccines are slightly (a few to several percent) less effective in preventing infection with the delta variant of coronavirus.

This does not change the fact that for any individual, vaccination is the surest way to prevent a severe course of COVID-19, while for society only universal vaccination will minimize the risk of another lockdown, inefficiency of the public health system (unavailability of doctors, ambulances, hospital beds, ventilators, etc.) and all the economic and social consequences known from previous waves of pandemics.

Collective resilience a chance for normalcy?

The concept of collective immunity (a.k.a. population immunity, herd immunity or group immunity) arose from the observation that the presence in a population of people immunized against a given disease reduces the likelihood that non-immunized people will also contract the disease. The concept applies to diseases that transmit from person to person, as is the case with the SARS-CoV-2 coronavirus.

The threshold for collective immunity is defined as the percentage of immunized persons in the population, after which the number of new infected persons begins to decline. The percentage of people immunized by vaccination varies from disease to disease. For example, in the case of measles, such a “safety threshold” is as high as 95%, for whooping cough it is estimated at 92-94%, diphtheria and rubella at 83-86%, mumps at 75-86%, which means that so many people in the population must be immune to a given disease in order to prevent larger-scale infections.

Thanks to collective immunity, vaccination protects not only the vaccinated, but additionally the most vulnerable people who cannot be vaccinated due to contraindications (such as infants or some chronically ill patients). The more people vaccinated, the greater the collective immunity, the more we are all protected from dangerous infectious diseases.

At the beginning of the coronavirus pandemic, it was assumed that for the phenomenon of collective immunity to arise, immunity through vaccination or COVID-19 must be achieved by about 70-80% of the population. However, because subsequent coronavirus variants, particularly the currently dominant delta variant, are more infectious, researchers suggest that this percentage of the population should be around 90%.

More than 2.6 million people have recovered and less than 20 million people are immunized through vaccination. These figures show that immunity has only been acquired by about half of our country’s population (the total number of people who have acquired immunity is less than the sum of the two groups, because many COVID-19 survivors were later vaccinated).

More than 4 billion doses of the vaccine have been administered worldwide to date, but only less than 15% of the population is fully immunized. More than 4 million people have died worldwide due to COVID-19.

People who have been vaccinated or who have had COVID-19 can become infected with coronavirus, but the disease almost always (except in severely ill, immunocompromised people) progresses as a mild viral infection. Vaccination protects against severe COVID-19, as evidenced, among other things, by the fact that in the first six months of 2021 in the US, 99.5% of hospitalizations due to COVID-19 involved unvaccinated individuals.

Worldwide studies show that by far the strongest immunity is obtained by people who have been vaccinated after contracting COVID-19 (it is perfectly safe to vaccinate survivors), so all the more reason why people who only suspect or are unsure whether they have contracted coronavirus infection should be vaccinated.

Principles of vaccine administration

Vaccines from BioNTech/Pfizer, Moderna and AstraZeneca are taken in two doses, the Janssen vaccine is single-dose. With two-dose vaccines, full protection is not achieved until several days after the second dose is taken.

The efficacy of COVID-19 vaccines is constantly monitored, including in the context of subsequent emerging mutations. These are standard efficacy studies of all approved medical preparations (so-called Phase IV clinical trials). Further clinical trials are being conducted to authorize the use of vaccines in increasingly younger age groups of children.

Taking into account the results of the studies, many countries have decided to require a third dose of the vaccine (the so-called booster dose), which prevents the level of antibodies against SARS-CoV-2 from decreasing several months after vaccination.


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