Washington, Jun 27 (IANS): There is currently no data to support that a Covid-19 vaccine booster shot is needed for the general population, according to the US Centers for Disease Control and Prevention. But, an extra dose may be needed for more-vulnerable groups, such as older adults or organ transplant patients.

However, public health officials will continue to monitor the virus to determine if additional shots are warranted in the future, said the CDC's Advisory Committee on Immunisation Practices, CNBC news reported.

"Boosters may be required for a broad population. However, it could also be that the need for boosters of Covid vaccine may only be demonstrated in some populations," Sarah Oliver, co-lead of the working group and a medical epidemiologist with the CDC's National Center for Immunisation and Respiratory Diseases, was quoted as saying.

According to the committee, rising cases of Covid infections in fully vaccinated individuals may be a clear indicator to decide whether boosters are needed, NBC news reported.

But if certain surrogate measures -- like waning antibody or T cell levels -- could be identified, boosters could potentially be given to prevent a rise in cases.

It is still unclear what those cutoff levels, called correlates of protection, might be, Sharon Frey, clinical director of the Center for Vaccine Development at Saint Louis University Medical School, was quoted as saying.

"I think the only thing we can do at this moment is, if we start to see an uptick in reinfection in people, or new infections in people who have been vaccinated, that's our clue that we need to move quickly," Frey said.

Both Pfizer and Moderna are investigating a third dose of Covid vaccine, while Johnson & Johnson is studying the need for a second dose to raise protection against the virus, the report said.

The US NIH's National Institute of Allergy and Infectious Disease, or NIAID, is also conducting a clinical trial to understand whether a third shot of a Moderna vaccine could be given after a person initially received two shots of Pfizer, or one shot of Johnson & Johnson, the report added.