Second boosters have been approved for adults 50 and older, as well as some people with weakened immune systems, since late March. However, younger adults are only entitled to one booster dose, which was approved in November. The feds are trying to move quickly to approve a second booster for all adults, the source said. Some experts are concerned that the immunity of younger adults may be waning as Covid-19 cases increase with the BA.5 Omicron subvariant predominating. Re-infections are more likely with BA.5 than with any previous variant because of its immune evasion characteristics, Dr. Eric Topol, a cardiologist and professor of molecular medicine at Scripps Research, told CNNI on Monday. The US Centers for Disease Control and Prevention reports that the BA.4 and BA.5 subvariants account for more than 70% of new infections in the country. But while these subvariants may partially escape the immunity produced by the vaccine and previous infection, vaccination still protects against serious disease. It remains unclear how many American adults would receive a second booster dose if one is approved. As of Thursday, about half of Americans 18 and older who were eligible for a first booster had gotten one, according to the CDC. Just over a quarter of eligible adults 50 and older have received a second reminder. A study published in May found that a fourth dose of Moderna’s or Pfizer/BioNTech’s mRNA Covid-19 vaccine provides a “substantial” boost in immunity to similar or even better levels than a third dose. The study, which was published in the medical journal The Lancet and included participants whose average age was 70.1 years, also showed that some people who had higher antibody levels before the fourth dose of the Covid-19 vaccine had only “limited” enhancement. Those with a history of Covid-19 infection had a similarly limited response. The authors say this suggests there may be a ceiling or maximum response that can come with a fourth vaccine dose. Two previous studies from Israel, conducted in participants aged 60 and older, showed that hospitalization and death rates from Covid-19 could be reduced with a fourth dose of vaccine given at least four months after the third dose. The reduction in hospitalizations and deaths was sustained over time with this fourth shot. This story has been updated with additional information Monday. CNN’s Jen Christensen contributed to this report.
