Coronavirus Vaccines How it works and side effects Everyday Science

Coronavirus Vaccines: How it works and side effects


Several vaccines against COVID-19 are being studied and developed worldwide to try to combat the pandemic caused by the new coronavirus. So far, only the Pfizer coronavirus vaccines are approved by the WHO, but many others are in the process of being evaluated.

The 6 vaccines that have shown the most promising results are:

Pfizer and BioNTech (BNT162): the North American and German vaccines were 90% effective in phase 3 studies;

Moderna (mRNA-1273): the North American vaccine was 94.5% effective in phase 3 studies;

Gamaleya Research Institute (Sputnik V): the Russian vaccine was 91.6% effective against COVID-19;

AstraZeneca and University of Oxford (AZD1222): the English vaccine is in phase 3 studies and in the first phase it showed 70.4% effectiveness;

Sinovac (Coronavac): the Chinese vaccine developed in partnership with the Butantan Institute demonstrated an efficacy rate of 78% for mild cases and 100% for moderate and severe infections;

Johnson & Johnson (JNJ-78436735): according to the first results, the North American vaccine appears to have efficacy rates ranging from 66 to 85%, with this rate varying according to the country where it is applied.

Coronavirus vaccines

In addition to these, other coronavirus vaccines such as NVX-CoV2373, from Novavax, Ad5-nCoV, from CanSino, or Covaxin, from Bharat Biotech, are also in phase 3 of the study, but still do not have published results.

How COVID-19 Vaccines Work?

Vaccines against COVID-19 have been developed based on 3 types of technology:

  1. Genetic technology of messenger RNA: it is a technology most used in the production of vaccines for animals and that makes healthy cells in the body produce the same protein that the coronavirus uses to enter cells. In doing so, the immune system is forced to produce antibodies that, during an infection, can neutralize the protein of the true coronavirus and prevent the infection from developing. This is the technology being used in Pfizer and Moderna vaccines;
  2. Use of modified adenoviruses: consists of using adenoviruses, which are harmless to the human body, and genetically modifying them so that they act in a similar way to the coronavirus, but without risk to health. This causes the immune system to train and produce antibodies capable of eliminating the virus if infection occurs. This is the technology behind vaccines from AstraZeneca, Sputnik V, and the vaccine from Johnson & Johnson;
  3. Use of inactivated coronavirus: an inactivated form of the new coronavirus is used that does not cause infection or health problems, but allows the body to produce the antibodies necessary to fight the virus.

All of these ways of functioning are theoretically effective and already work in the production of vaccines for other diseases.

How is the vaccine’s effectiveness calculated?

The rate of effectiveness of each vaccine is calculated based on the number of people who developed the infection and who were actually vaccinated, compared to those who were not vaccinated and who received a placebo.

For example, in the case of the Pfizer vaccine, 44,000 people were studied and, of that group, only 94 ended up developing COVID-19. Of those 94, 9 were people who had been vaccinated, while the remaining 85 were people who had received the placebo and therefore did not receive the vaccine. According to these figures, the effectiveness rate is approximately 90%.

Is the vaccine effective against new variants of the virus?

According to a study carried out with the vaccine from Pfizer and BioNTech, antibodies stimulated by the vaccine have been shown to remain effective against new variants of the coronavirus, both the mutation in the United Kingdom and South Africa.  

In addition, the study also points out that the vaccine should remain effective for 15 other possible mutations of the virus.

When did the first vaccines arrive?

The first vaccine against COVID-19 was released for distribution in January 2021. This was only possible due to the creation of several special programs that allow the emergency release of vaccines without having to go through all the approval phases outlined by WHO.  

In normal situations and according to the WHO, a vaccine should only be released to the population after completing the following steps:    

  • The laboratory that produces the vaccine needs to carry out large-scale phase 3 studies that show satisfactory results for safety and efficacy;
  • The vaccine needs to be evaluated by entities independent of the laboratory, including the country’s regulatory body
  • A group of researchers chosen by WHO analyzes the data obtained from all tests to ensure safety and effectiveness, as well as to plan how each vaccine should be used;    
  • WHO-approved vaccines must be able to be produced in large quantities;
  • It is necessary to ensure that vaccines can be distributed to all countries with great rigor.

WHO has joined forces to ensure that the approval process for each vaccine proceeds as quickly as possible, and regulators in each country have also approved special authorizations for COVID-19 vaccines.

ALso Read: Why is there still no vaccine against coronavirus?

Who can get the vaccine?

The guideline is that all people can be vaccinated safely, whether or not they have had a previous COVID-19 infection. Although studies indicate that after infection the body develops natural defenses against the virus for at least 90 days, other studies also indicate that the immunity conferred by the vaccine is up to 3 times greater.

Complete immunity from the vaccine is only considered active after all doses of the vaccine are administered.

In any case, having had the vaccination or having had a previous infection with COVID-19, it is recommended to continue to adopt individual protection measures, such as wearing a mask, frequent hand washing, and social distance.

Also Read: When will the COVID-19 pandemic end?

Possible side effects

The possible side effects of all vaccines being produced against COVID-19 are not yet known. However, according to studies with vaccines produced by Pfizer-BioNTech and the Moderna laboratory, these effects appear to include:

  • Pain at the injection site;
  • Excessive tiredness;
  • Headache;
  • Fever and chills;
  • Joint pain.

These side effects are similar to those of many other vaccines, including the common flu vaccine, for example. 

As the number of people increases, more serious adverse reactions, such as anaphylactic reactions, are expected to appear, especially in people who are more sensitive to some components of the formula.

Who should not get the vaccine?

The vaccine against COVID-19 should not be administered to people with a history of severe allergic reactions to any of the components of the vaccine. In addition, vaccination should also only be carried out after a doctor has evaluated it in the case of children under the age of 16, pregnant women, and breastfeeding women.

Patients using immunosuppressants or autoimmune diseases should also be vaccinated only under the supervision of the treating physician.

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