A third dose of the mRNA COVID-19 vaccines (Pfizer or Moderna) is identical to the first two doses. It can help protect people with weakened immune systems who did not have a strong enough response to the first two doses of one of the mRNA vaccines. Such people can get a third dose as soon as 28 days after a second dose. The FDA has authorized, and the CDC recommends, that those with certain medical conditions that suppress the immune system get a third dose of the same brand of COVID-19 vaccine that they initially received.
The virus defeated the first two shots and was strengthened in the process. No doubt the new and improved virus will overcome a third shot rather quickly. No wonder Israel is already planning a fourth