How long after vaccination against SARS-CoV-2 do we become immune?

Coronaviruses are a family of viruses named as such because when seen under an electron microscope, their appearance is rounded, and they are surrounded by a crown formed by spikes or small spicules at the end of which there is a glycoprotein called S. These are used for the virus to attach itself and enter the cells of the infected person, just like a key that fits into a lock, the lock being a protein present in the body’s own cells, ACE2, to which the infecting virus attaches itself to make its way through.

The vaccines currently used to immunize against SARS-CoV-2 target the virus by exposing the immune system to the S protein of the virus.

Since the immune system possesses memory, it can then use the vaccine to analyze and store information about the S protein and draw upon this information to protect you if exposed to the actual virus in the future.

However, immunity doesn’t occur immediately after vaccination. In fact, it usually takes approximately 2 weeks for your body to develop immunity. So, you can still get sick during this time.

It takes approximately 10 days after the first dose of the vaccine for antibodies to start producing a response that can recognize the SARS-CoV-2 protein S.

Similarly, it takes a week or longer for the T-cells to start responding to the vaccine.

The 2nd vaccine dose activates the immune system much more rapidly. Therefore, two weeks after the second dose, your antibody levels increase more than ten-fold, providing a much stronger and longer-lasting protection against infection.

The importance of the 2nd vaccine dose

Most vaccines for immunization against SARS-CoV-2 are designed to be administered in two doses, the first dose jump-starts the immune system response, but the second dose is essential to ensure that immunity is strong, consistent person-to-person and longer lasting.

When are you fully vaccinated?

  • 2 weeks after the second shot in 2-dose format vaccines.
  • 2 weeks after a single-dose vaccine, such as Johnson & Johnson’s Janssen COVID-19 vaccine.

You are not fully vaccinated if:

  • It has been less than 2 weeks since your single-dose vaccine.
  • It has been less than 2 weeks since your second shot of a 2-dose format vaccine.
  • You still need to get your second dose of a 2-dose vaccine.