When taking 3ª and 4ª dose of COVID-19 vaccine?

Third dose: means that to achieve the necessary level of protection, a vaccine needs to be administered in 3 equal initial doses;
Booster dose: means that after receiving all the initial doses of a vaccine, the person receives a different dose to boost immunity. This dose may contain samples of the most recent variants of the virus, also serving as an "update" of the immune response.

Currently, doses being administered in addition to the primary vaccination schedule are "booster doses", as they are given to reinforce the immunity conferred by the initial doses. In Brazil, people aged 40 and over and he althcare workers must still receive a "4th dose", also called a 2nd booster dose, given 4 months after the first booster dose ("3rd dose").

When to take the "3rd dose"

Enter your details in our calculator to find out from what date you can take the 3rd dose (1st booster dose) and which vaccine you can take:

In Brazil

The booster dose should be administered at least 4 months after completing the initial vaccination schedule ^{[1] However, the vaccination schedule and vaccine indication may vary in some states, so it's important to be aware of local recommendations.}

In case the initial dose was with Janssen, it is indicated that the first booster is given after 2 months of the initial dose and that the second booster dose (3rd dose) is given after 4 months.

In the case of recent infection with COVID-19, the recommendation is to wait 4 weeks after the onset of symptoms or 4 weeks after the first positive result, in the case of asymptomatic people, to take the booster dose of the vaccine against to COVID-19.

In Portugal

The booster dose must be given at least 6 months after the initial doses or after a more recent COVID-19 infection and must be given with the Pfizer or Moderna vaccine, regardless of the vaccine administered in the initial vaccination schedule.

When to take the "4th dose"?

In Brazil, adults aged 40 and over and he althcare workers should receive a 2nd booster dose (the "4th dose"), given 4 months after the "3rd dose", which can be Pfizer, Astrazeneca or Janssen. In addition, for people who started the vaccine regimen with Janssen, are over 40 years old and are not pregnant or have recently given birth, the "4th dose" is also indicated 4 months after the "3rd dose".

In Portugal

In Portugal, the second booster dose is indicated for people aged 80 and over and residents of nursing homes. This dose should be given 4 to 6 months after the first booster dose or SARS-CoV-2 infection, and should be the same as the first booster, which can be done with Pfizer or Moderna.

When does the booster start to take effect?

A study carried out by Pfizer ^[3] indicated that the protection against coronavirus provided by its vaccine starts to be effective from the 7th day post-vaccination. Another study done in the UK ^{[4], with the Pfizer vaccine, also found that protection levels are quite high after 2 weeks of administration of the booster dose.}

What are the risks of a new dose

Information about the risks of a new dose of COVID-19 vaccine is still limited. However, reactions to the booster dose of mRNA or adenovirus, which are Pfizer and AstraZeneca respectively, are similar to the two previous doses, with mild to moderate symptoms such as excessive tiredness or pain at the injection site being expected.

Also, other common side effects include redness or swelling around the injection, headache, muscle pain, chills, fever, or nausea. Check out all the side effects of COVID-19 vaccines and what to do to alleviate them.

What to do in case of COVID-19

If you have symptoms of COVID-19, have been in contact with someone who has tested positive, or has a positive test, fill in your details and learn what to do:

option=b, @block-A1"' > I tested positive for COVID-19.
option=c, @block-A1"' > I have symptoms suggestive of COVID-19.
option=d, @block-A1"' > I've been in contact with positive case.
option=f, @block-F1"' > I've had COVID-19, but I still have symptoms.
option=e, @block-A1"' > I want to know more information.

country=en, @block-B1"}, {"condition":"option=c", "action":">country=en, @block-C1"}, {"condition":"option=d", "action":">country=en, @block-D2"}, {"condition":"option=e", "action":">country=en, @block-E1"}]' > Portugal
country=br, @block-B1"}, {"condition":"option=c", "action":">country=br, @block-C1"}, {"condition":"option=d", "action":">country=br, @block-D1"}, {"condition":"option=e", "action":">country=br, @block-E1"}]' >

Self-test.
Rapid antigen test.
RT-PCR.

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I have no symptoms.
I only have mild symptoms (fever, cough, tiredness, headache, sore throat, loss of taste…).
I have moderate symptoms (very intense cough, some shortness of breath, excessive tiredness…).
I'm really short of breath.

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No.
I did a self-test
I did a rapid antigen test.
I did RT-PCR test.

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RT-PCR for COVID-19: when to do it and results

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test=0"' > Negative
test=1"' > Positive

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It is possible that your symptoms are a sign of another infection, such as the flu or H3N2, for example. Still, we advise you to repeat the COVID-19 test within the next 3 days. Check out the differences between flu, COVID-19 and a cold.

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risk=1, @block-D5"' > I live with the person who tested positive.
I have been in direct contact with the positive person (less than 2 meters) for more than 15 minutes and I am a he alth professional or work in an institution for the elderly.
risk=0"' > The person who tests positive does not live with me.

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Yes.
No.

Your contact is considered high risk. You do not need to isolate yourself, but you must maintain all personal protective measures for 14 days, be aware of the appearance of symptoms and perform a COVID test as soon as possible (rapid test or RT-PCR). If the result of the 1st test is negative, you must repeat the test between the 3rd and 5th day after contact with the positive person.

COVID-19 rapid test: how it is done, where to do it and results

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RT-PCR for COVID-19: when to do it and results

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Your contact is considered low risk. For this reason, you don't need to do isolation, or perform COVID test. However, you must maintain all individual protection measures (such as wearing a mask and avoiding unnecessary travel) and be aware of the appearance of symptoms in the next 14 days.