Why do I have more adverse reactions to the second dose? An infectious disease specialist explains the Pfizer and Moderna vaccines.
There is still no sign of an end to the spread of the new coronavirus.
In the series “Consultation Room with a Great Doctor,” doctors specializing in various fields provide easy-to-understand explanations of health-related problems, such as how to prevent and deal with diseases.
In this installment, Dr. Takashi Matono, Director of the Department of Infectious Diseases at Iizuka Hospital in Iizuka City, Fukuoka Prefecture, talks about mRNA (messenger RNA) vaccines, why adverse reactions occur after vaccination, and what to do in the event of an adverse reaction.
Why adverse reactions are stronger after the second vaccination
Dr. Takashi Matono, Director, Department of Infectious Diseases, Iizuka Hospital:
This time, there are two-dose vaccines in circulation. Both Pfizer and Moderna have to be given twice, but pain at the site of the injection occurs at a certain frequency whether it is the first or second time. Since the needle is inserted into the muscle, it is the same as the so-called bruised pain.
This is not about the reaction, but simply the pain at the place where it was injected. It depends on the person, but it is said that 60 to 80% of people will feel it to some extent. Don’t be too afraid there. It will definitely get better within a few days.
The other is the reaction of the whole body. Symptoms such as fever, aching joints, and laziness are reported to be more common after the second vaccination.
What I mean by this is that the first dose of the vaccine is said to build up about 70% immunity in the body. (In the case of wild strains: non-mutated strains)
The second dose of the vaccine is 94-95% effective and lasts longer. We call it a booster, but since the second dose is given to increase the effectiveness and make the vaccine last longer, the body’s response is clearly stronger with the second dose.
It depends on the age of the person, but it is said that the second vaccine causes fever in about 10% of people over 65 years old and 30-40% of people between 30 and 40 years old. This is quite a high frequency.
However, the symptoms of fever and slight laziness occur the day after the vaccine is given, but do not last for more than a few days afterwards.
On the other hand, there are people who are worried about whether they are really immune to the vaccine even though they did not have fever or fatigue. In other words, it is not a one-to-one correspondence.
There is no need to be anxious whether you have systemic symptoms or not; I think the intensity of anxiety when you have an adverse reaction differs depending on whether you know that your body is likely to react after the second time or not.
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