Second dose of Pfizer vaccine, the infectious disease specialist: “More acute side effects? Is it because the immune system is already activated”

Second dose of Pfizer vaccine, the infectious disease specialist: “More acute side effects? Is it because the immune system is already activated”
Second dose of Pfizer vaccine, the infectious disease specialist: “More acute side effects? Is it because the immune system is already activated”

The Pfizer vaccine is one of the first weapons used in Italy to fight Covid. It is the serum that inaugurated the great mass vaccination. It is a mRNA (messenger RNA) vaccine against COVID-19 (modified at the nucleoside level). To achieve effectiveness it is divided into two injections, usually in the upper arm muscle, at least 21 days apart. It is possible to extend the second dose, in any case no later than 42 days from the first (Circulars 9 April and 5 May 2021).

It is stored in special freezers at a temperature between -90 ° C and -60 ° C, in the original packaging. IS also recommended for children aged 12 and over. Few have complained of side effects after the first dose, but what happens after the second dose? The Reformist he asked Ivan Gentile, Full Professor of Infectious Diseases at the University of Naples Federico II and Director of the Complex Operating Unit of Infectious Diseases of the Federico II University Hospital to explain in detail everything there is to know about the second dose of the Pfizer vaccine.

What are the side effects of the second dose of the Pfizer vaccine?

The most common side effects are soreness or pain at the injection site, headache, body aches, tiredness and fever. Other effects such as itching, pain in the limbs, swollen lymph nodes, difficulty falling asleep have affected less than one in 100 people and are therefore less common. The side effects are most common after the second dose in the case of the Pfizer vaccine (similarly to what happens for the Moderna vaccine) and generally of lesser severity in older individualsprobably because young people have a more reactive immune system.

Why are side effects more acute with the second dose than with the first?

Because the second dose is generally more immunogenic, that is triggers a more pronounced immune reaction than the first dose. In fact, the immediate physical reaction to the COVID-19 vaccine is caused by mechanisms that attract white blood cells to the injection site and this results in the appearance of local and systemic symptoms. However, it is at a later stage of the immune response that specific antibodies against the virus are produced through the expression of the surface protein induced by the vaccine. It follows that after the second dose of the vaccine, three weeks after the first administration, the immune system is already activated with consequent intensification of reactive clinical symptoms.

Can everyone have the same side effects after the second dose of the Pfizer vaccine?

Absolutely not. Our immune system has unique and peculiar characteristics in each of us: it is linked to both genetic and environmental factors. For this reason the intensity of the symptoms varies greatly from individual to individual.

Are there particular categories that are more likely to experience side effects after the second dose of the Pfizer vaccine?

Generally, symptom intensity was greatest in women and in subjects under the age of 60.

Does the risk of thrombosis increase after the second dose of Pfizer vaccine?

I would say that in general such a vaccination it is not related to a higher incidence of thrombotic events.

What symptoms should be looked out for after the second dose of Pfizer vaccine and if they appear what to do?

Both after the first and the second dose it is important to be careful in weeks after vaccination, at the appearance of breathlessness, chest pain, leg swelling, persistent abdominal pain or nervous system symptoms (including severe headache, vision changes) as well skin spots such as bruising and redness, both near the injection site and at a distance. In this case, it is necessary to seek medical assistance quickly and contact specialized centers for the continuation of the diagnostic-therapeutic process of the case. It should be emphasized that these are extremely rare events.

How many days after the second dose of Pfizer vaccine are you completely immune?

Protective levels of antibodies directed against the SARS-CoV-2 virus have been found to 2 weeks from the second dose.

What does it mean that the vaccine is active? Will I no longer take Covid?

It means that the vaccine has shown protection against the virus, that is, in studies among vaccinated subjects theincidence of COVID-19 disease and, above all, of severe forms requiring hospitalization it was extremely lower than in unvaccinated subjects. The protection provided by the vaccine is 95% and in any case the few vaccinated subjects who became infected did not have serious disease.

How long does the protection last after the second dose?

At present there are insufficient data on the duration of protection offered by vaccination, although several studies have shown the persistence of adequate and protective antibody levels 6 months after vaccination.

Could there be a third dose of Pfizer vaccine at the end of the summer as well?

A third dose of the vaccine could be useful in case of appearance of any viral variants capable of evading the immune response induced by the vaccine and for which the need for an immunological booster can be predicted by means of a third dose. To this end, the Pfizer company has launched a study on 600 volunteers (aged 65 or over) who will be co-administered the pneumococcal vaccine and a third dose of the Covid-19 vaccine. The response of the subjects in the 6 months following the administration of both vaccines and their safety profile will then be assessed. It must be said that the first vaccines were put on the market less than 6 months ago. We therefore have no long-term data that can give a definitive answer to this question.

What is the value of the antibody test and how should it be interpreted?

The anti-SARS-CoV2 antibody tests on the market are many, directed against different viral antigens and with non-standardized positivity thresholds and for which they are recommended to be read and interpreted by medical specialists. The utility consists exclusively in the qualitative and non-quantitative evaluation the presence of antibodies to SARS-CoV2. In other words, we still do not have a correlative of protection, nor a threshold above which we can be sure that the patient is protected. At the moment we just need to know that the antibodies have been produced.

Is it useful to test for antibodies?

It may be useful for evaluating the actual development of vaccine-induced specific immune responses.

Is the antibody test useful in deciding whether or not to take the second dose of Pfizer vaccine?

It is not a correct procedure because, as stated above, there are no univocal antibody threshold values ​​unequivocally indicative of protection against the virus and it is not possible to predict how the blood levels of antibodies will change over time. Therefore, as also indicated by the National Institute of Health, the use of serological tests is not recommended for the purpose of vaccination decision making.

After the second dose of the vaccine, can you remove the mask and let your guard down?

There is insufficient evidence available regarding the efficacy of the vaccine not only in preventing the development of COVID-19 disease but also in preventing the subject from becoming infected and possible transmission to one’s contacts. It follows that even vaccinated subjects should maintain some protective measures, such as a mask, social distancing and careful hand washing. In the United States it is said “vaccinated or masked”. I believe that we too could adapt to this adage, starting by begging for outdoor masks for the vaccinated.

Professional journalist and videomaker, in 2006 he started writing for various national and local newspapers dealing with news, culture and technology. He attended the Suor Orsola Benincasa School of Journalism in Naples. Among the various publications with which Roma has collaborated, the AdnKronos news agency,, the OmniNapoli news agency, Canale 21 and Il Mattino di Napoli. Proudly Neapolitan, she mostly deals with video and videoreportage. She is the author of the documentary “Lo Sfizzicariello – stories of redemption from mental distress”, special mention at the Naples Film Festival.

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Rossella Grasso

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