DENVER (CBS4) – Doctors say a third dose of a COVID-19 vaccine could be most beneficial to those with a weaker immune system where the initial two shots were not enough to help them gain as much protection from the virus as others. The Food and Drug Administration amended its emergency use authorizations for the Pfizer and Moderna vaccines Thursday for immunocompromised individuals.

“It is the individual’s response that we’re really concerned about so if you have a normal immune system, right? You don’t need to go run out and get a third dose,” said Dr. Steve Frankel, professor of medicine and executive vice president of clinical affairs at National Jewish Health. “But if you have an impaired immune system and maybe you can make antibodies well, maybe you can’t, that’s when we really think about doing that third dose.”

The FDA said organ transplant recipients and those diagnosed with conditions where they are considered immunocompromised should receive a third dose. The Centers for Disease Control and Prevention has a meeting scheduled Friday for one of its advisory committees to discuss recommendations.

“What we know is that if you’re immunocompromised taken broadly, you’re at risk of not having as robust a response to the vaccine,” Dr. Frankel told CBS4. “The vaccine stimulates your immune system, right? The vaccine doesn’t give you artificial antibodies, it doesn’t provide you protection like a medication would.”

Frankel says the move by these agencies should include the context of the current stage of the pandemic. Another surge in cases because of the Delta variant and a large population that is still unvaccinated contribute to their consideration. While the majority of those who are severely ill do not have the vaccine, there are some breakthrough cases.

“What a vaccine does is it stimulates your own immune system to mount a defense against the virus. If you’re immune system is normal and intact, great, fabulous, you’re in a really good place,” he said. “If your immune system does not work properly for any number of reasons, then you are immunocompromised and you may or may not mount a great response after receiving the vaccine.”

Cancer patients as well as those who take medications that suppress their immune systems to treat other conditions are among those in this current category likely to get an additional dose of the vaccine. Frankel says this decision is based on months of research looking at a third dose, where more studies are available for the Pfizer and Moderna vaccines as most Americans have either of those two options.

“As this goes on, as vaccine is more available, as we really try to optimize our strategy for keeping all of us safe and healthy, looking at folks that are over 65 or 70 makes a whole lot of sense,” he said.

Other countries have already started suggesting another dose for older adults because their immune system doesn’t have the same response as those who are younger and healthier.

More research is needed for the Johnson & Johnson vaccine, including if a second dose of the same shot would be ideal or if adults could take one of the other two choices for their booster dose. It is also required to determine if this vaccine will move in the direction of the flu shot, where it is recommended annually, considering the length of immunity over time and the impact of variants.

“It’s a possibility, it’s not for sure yes, it’s not for sure no, and it’s a little uncomfortable, right? because you have to accept that there’s some uncertainty as this goes on,” Frankel said.

As some get closer to a new, additional shot of Pfizer and Moderna after already getting two doses, he says it is still important that they especially follow the old guidelines for stopping the spread of the virus during the pandemic.

“We have always suggested to them, you really need to keep wearing a mask, you need to keep social distancing, we don’t know how well you’re going to make antibodies, we don’t know how well your immune system is going to respond, Frankel said. “Be prudent. Be cautious.”

LINK: FDA Announcement