In an ever-changing situation, we’ll try to keep you updated on COVID-19 vaccines and attempt to answer the main questions about dose administration, the duration of vaccination, the duration of acquired immunity and other associated issues.

As of January 14th 2021, 32 million people worldwide have been vaccinated (click here for full data). Vaccinations have been performed with different vaccines in 19 different countries across the globe. Vaccines in use have different characteristics, starting with the technology on which they’re based, and the storage that affects the logistics of dose administration.

  1. What are the characteristics of the main COVID-19 vaccines?

Most of the vaccines already available (or those about to be approved by the various regulatory bodies) are administered in two doses. The reason lies in the fact that a double-dose (administered over a specific period) stimulates the immune system more, in order to produce the neutralizing antibodies that serve in fighting the virus. In addition, since the vaccine doesn’t contain the virus (and cannot cause infection), it’s therefore necessary for the immune system to encounter the viral antigens (Spike proteins) several times to produce neutralizing antibodies and memory cells (i.e. T and B lymphocytes, capable of remembering the antigen for a long time).

Here are the differences between the three vaccines currently on the market across Europe.


  • Clinical trials have been performed on over 43,000 people
  • It’s an mRNA vaccine that must be stored at -70 degrees Celsius, but can be stored at 4 degrees Celsius for the five days immediately prior to its administration
  • It must be administered in two doses, 21 days apart


  • Clinical trials have been performed on over 30,000 people
  • It’s an mRNA vaccine that must be stored at -20 degrees Celsius
  • It must be administered in two doses, 28 days apart

AstraZeneca-Oxford University (under approval by AIFA):

  • Clinical trials have been performed on over 65,000 people
  • It’s a vaccine that uses an adenovirus as a viral vector and can be stored at 4 degrees Celsius
  • It must be administered in two doses
  1. Can you become ill between the administration of the first and second dose?

Since efficient immunity from vaccination occurs one week after the administration of the second dose, it’s possible to become infected with SARS-CoV-2.

This is true for all vaccinations, as no vaccine protects the vaccinated person immediately. In fact, it’s possible to catch the normal flu, even immediately after being vaccinated, precisely because of the stimulation of the immune system and the consequent production of antibodies needed to recognize the virus takes time.

  1. If, after the first dose of vaccine you become positive for the virus, can you continue with the administration of the second dose?

There are no contraindications to continuing with the vaccination, in the case of becoming positive for SARS-CoV-2 after the first dose of the vaccine. The antibodies that will develop naturally (following the infection) will add to those stimulated by the vaccine, therefore increasing the protection of the infected person.

  1. Following the vaccination, can I test positive from a molecular or antigenic swab?

The molecular swab detects the presence of SARS-CoV-2; the vaccine doesn’t inject any virus, so it can’t result in any positivity. The antigenic swab detects virus antigens, like the molecular swab. The antigenic swab is performed with nasopharyngeal swabbing, and the vaccine is administered with an intramuscular puncture, therefore no antigens will be found in the nasopharyngeal mucosa.

  1. When does the immunity acquired following the vaccination actually begin?

It depends on the vaccine being administered. Generally, we can say that immunity is effectively stimulated about one week after the administration of the second dose of vaccine.

  1. Will it be necessary to have a booster shot every year?

This is not yet known, as it is not known how long immunity may last. This depends on several factors, among which, it’s important to mention the ability of RNA viruses to mutate. If we take, for example, another RNA virus that we all know well; the influenza virus, we know that it’s necessary to receive a vaccination shot every year, in order to stimulate the immune response towards any new strain of virus.

In addition, there are other pathogens for which a booster vaccination is required in adulthood, because memory cells are reduced over time. For example, a booster is required in the case of vaccination against tetanus, diphtheria and pertussis (i.e. infectious agents of a bacterial origin).

  1. Who will monitor adverse reactions?

AIFA (Agenzia Italiana del Farmaco), or the Italian Medicines Agency for Italy, in addition to the pharmacovigilance activities normally provided for drugs and vaccines (i.e. based on ad hoc reports and pharmacovigilance networks already in place), will promote the launch of some independent post-authorization studies on COVID-19 vaccines.

The surveillance activities will cover both the collection and evaluation of spontaneous reports of suspected adverse reactions (so-called passive pharmacovigilance) and proactive actions, through studies/projects of pharmaco-epidemiology (so-called active pharmacovigilance).

AIFA has set up a Scientific Committee in Italy, which, for the entire period of the vaccination campaign, will have the function of supporting the Agency and the Scientific Heads of the individual studies in the phase of setting up activities, in the overall analysis of the data that will be collected and in the identification of possible interventions. The goal is to have (also through an international collaborative network), the ability to highlight any sign of risk and at the same time, to compare the safety profiles of different vaccines that will become available and to provide recommendations.

It will be the responsibility of the attending physician and the various vaccination centers to report cases of adverse reactions, so as to ensure an immediate reaction and to guarantee the necessary safety of vaccines.

This post is also available in: Italiano


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