Why some vaccines require a second dose

ABC

Madrid

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The three vaccinations that are already being administered in Europe, that of Pfizer, the of Modern and of AstraZeneca, they need two doses to be fully effective. The second dose increases the effectiveness of the first and the production of antibodies capable of protecting us against the coronavirus.

Why some vaccines require a second dose

As explains the Spanish Agency for Medicines and Health Products, most currently licensed vaccines require at least two doses for maximum efficiency. This is so because the first contact with the vaccine antigen is only capable of triggering a certain level of protection and this multiplies with subsequent doses of the same.

In addition, prior to their approval, the Pfizer, Moderna and AstraZeneca vaccines have been evaluated and clinical trials have been conducted to determine how to administer the dose, or the doses in these cases, to inject them safely, without risk of serious side effects, and what are you for improve immunogenicity, that is, the neutralizing antibody response. It was observed that a single dose was not enough in these vaccines.

How many days to wait between doses

It is recommended in the case of mRNA vaccines, that is, those that use Messenger RNA for the human organism to react by generating neutralizing antibodies against the coronavirus, wait a period between 21 and 28 days. Pfizer and Moderna they would be within this group.

Based on the data available from studies of vaccines of this type, experiments were conducted with a large number of people using vaccines and placebos, using two doses and separating them from each other about three weeks. Clinical trials showed that this second dose and in this period of time managed to improve the efficacy of the vaccine by stimulate the creation of antibodies against Covid-19.

Vaccine studies state that in the first 10 days after administering the first dose, around a 50% protection against SARS-CoV-2.

AstraZeneca, a different vaccine

The case of the vaccine AstraZeneca is different. This vaccine is made from a type of virus called adenovirus, which often causes colds among chimpanzees. To make the vaccine, the researchers altered a gene for a coronavirus protein so that the human immune system could recognize the true coronavirus in the event of a contagion.

At first, as reported by the Reuters agency, it was intended to administer a single dose to the study participants. However, due to a mistake, they began to administer half the amount needed. For this reason they began to put a booster dose after a month.

It was found that when a single dose was administered the efficacy was 60%, while with the two separate doses the efficacy of the same increased to 90%.

Do second doses have side effects?

According to FDA (U.S Food & Drug Administration), the most frequently reported side effects after administering any of the doses of the Pfizer son:

Pain at the injection site.

Fatigue.

Headache.

Muscle pain.

Shaking chills.

– Pain in the joints.

Fever.

People who have been vaccinated with the two required doses report that they experienced these effects more intensely after being vaccinated with the second dose.

Something similar occurs in the case of Modern: the second dose it usually causes more side effects than the first. However, it should be remembered that these symptoms are mild and disappear in a short time. These are:

Pain at the injection site.

Fatigue.

Headache.

Muscle pain.

Shaking chills.

– Pain in the joints.

Swollen glands lymphatics in the same arm as the injection.

Nausea and vomiting.

Fever.

AstraZeneca It cannot yet be applied in the United States (it has not been approved by the FDA), but it can be applied in Europe, since it has received approval from the European Medicines Agency. However, it presents side effects similar to the previous ones, as stated by the British government on its website:

Pain or itching at the injection site.

Fatigue.

Discomfort general.

Shaking chills.

Headache.

Fever.

Sickness.

Muscle pain.

Joint pain.

It has been proven that, unlike the other two, you are more likely to experience some of these mild symptoms when administering the first dose.

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