Third (booster) dose for Covid-19 vaccine

Third (booster) dose for Covid-19 vaccine

Israel was the first country to implement an additional nationwide vaccine campaign for a third dose against Covid-19. The rationale for this campaign was based on an observation in immunocompromised patients. In this specified population, there was an insufficient rise of antibodies after two doses while those who were vaccinated in a third dose demonstrated a significant rise in their antibody’s level. Although over 5 million people had been already vaccinated with 2 doses of the Pfizer vaccine, it was hypothesized that the striking rise of Covid-19 total and severe cases with the lambda variant is due to wanning immunity. Thus, the Israeli ministry of health decided to first vaccinate in the booster dose at risk older population, and after an early positive sign of an effect in reducing infection rate and severe cases, it was recommended for all population.

Other countries like the United states and the United Kingdom are preparing for a similar campaign in selected populations.

In this short chapter we will try to explain about this third dose for the Covid-19 vaccines.

What is the meaning of the term booster?

The term is also common in many other vaccines. It means that this additional dose is intended to give a boost to the immune response to the virus.

Why is a booster necessary or what is waning immunity?

We are familiar with the term “waning immunity” from other vaccines. It means that even after getting vaccinated, the antibodies levels go down over time. And when they go down, we become less protected. So, sometimes we need to give our immune system some kind of a reminder. This booster dose reminds our immune system to re-produce high levels of antibodies against Covid-19.

The thought is that a booster of the vaccine will increase the antibodies level to a degree that could prevent the contamination by the new variant or at least will protect those who had been vaccinated from severe illness or complications. Those antibodies will give the vaccinated people a renewal protection against Covid-19.

Who needs to get the booster?

Initially, the third vaccine campaign was aimed for people who are more vulnerable to Covid-19 complications. First, immunocompromised patients, then older people or patients with chronic diseases. It is similar to the priorities determined initially for the first dose (those who are at risk). Because of early positive signs of reducing infections and severe cases in these populations, the campaign has been extended in Israel to all people ,including healthy, in an attempt to control the rising numbers of infected people in the entire population.

In the United States it was recommended to give the booster shot to:

  • People ages 65 years and older.
  • Adults 18+ living in long-term care settings.
  • People ages 50–64 years with underlying medical conditions

It was also recommended to consider the booster to:

  • People ages 18–49 with an underlying medical condition/
  • People ages 18–64 who are at increased risk for COVID-19 exposure and transmission due to working or residing in certain settings

When can one get the booster?

In Israel, the ministry of health recommended the third booster dose at least 5 months after the previous second dose. The CDC stated the individuals will be eligible starting from 6 months after the second dose (immunocompromised patients should get a third dose at least 28 days after the second dose in an attempt to build a proper immune response).

What about someone who has already got Covid-19?

It is a matter of national policy. In Israel, those who got infected with Covid-19 are eligible for a single dose at least 3 months after recovery.

Does the booster have to be by the same company as the previous vaccines?

In Israel, practically everyone was vaccinated with the Pfizer vaccine and will receive a third dose of Pfizer vaccine. Interchangeability between the mRNA vaccines of Pfizer and Moderna is subjected for a national policy. In the USA for now, the Pfizer-BioNTech booster shot will be given only to people whose primary series was with the same (Pfizer) vaccine. People in the recommended groups who got the Moderna or J&J/Janssen vaccine will likely need a booster shot but should wait till the CDC publish new recommendations.

Are there more side effects after receiving the third dose?

I have seen all scenarios. People who didn’t suffer from any side effects after the first two doses but experienced illness similar to a light flu after receiving the booster, and the other way around. After over 1.5 million people have been vaccinated for third time, we can certainly say that no significant side effects were observed.

Is it not too much to receive three mRNA vaccines?

As we have seen, these are completely safe vaccines, therefore there is no problem in receiving a third dose. I have a feeling that this dose will not be the last Covid-19 vaccine we will get. 

Is it possible to get a serological test before receiving the third vaccine to decide whether to be vaccinated or not?

In my mind there is no significant meaning to a serological test result and I do not recommend this approach.

No one knows what is the required antibodies level that will provide protection, therefore I think the serological test, in this case, is unnecessary.

To conclude, in a pandemic as in a pandemic, there are new things that we learn as we go. Now it’s the time to give a booster and remind our immune system how to re-produce Covid-19 antibodies.


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