The emergence of a highly contagious submicron variant in the United States this spring appears to have reduced the vaccine’s defense against hospitalization of Covid. Reported by Centers for Disease Control and Prevention On Friday.
However, officials found that the first and second booster shots helped strengthen people’s defenses. Additional shots increased the level of protection of people against those Omicron subvariants and restored some of the protection lost over time from the last shot.
“Booster doses need to be obtained as soon as a person is eligible,” writes CDC scientists.
However, there are some notable caveats to the findings. Measuring vaccine efficacy is complicated by the number of unvaccinated people infected with the virus, especially during the proliferation of Omicron cases in winter.
These previous infections give people some protection against Covid. As a result, vaccines appear to be less protective than they really are in studies like the CDC that compare the results of the virus in vaccinated and unvaccinated people.
CDC scientists have sought to explain these difficulties by taking advantage of the lack of information about the patient’s history of infection. Agency scientists used data from hospitals in 10 states to investigate approximately 58,000 hospitalizations diagnosed with Covid-like illness from mid-December to mid-June. This study focused on adults with a healthy immune system.
By late April, the subvariants of Omicron, known as BA.2 and BA.2.12.1, outperformed the nationwide version of Omicron in the winter.
Studies have shown that after these subvariants became predominant, the Pfizer-BioNTech and Moderna vaccines were less effective at preventing people from being admitted to the hospital with Covid than during the winter Omicron wave. all right.
Two doses of the vaccine were 24% more effective for hospitalization after the mutant had taken over, compared to 61% during the period when the original version of Omicron was predominant. (These numbers are retained for those who received a second dose at least 5 months ago.)
The decline is probably due in part to the ability of subvariants to evade people’s immune defenses from vaccines, and in part to the fact that unvaccinated people have elicited some protection from previous infections. increase.
The benefits of these additional doses seemed to diminish over time, but booster doses helped considerably. When the subvariant became the primary source of infection, a third dose of Pfizer or Moderna increased the efficacy of the vaccine for hospitalization initially to 69% and after 4 months or more to 52%.
The third dose was more protective during the winter surge of the original version of Omicron.
The CDC approved a second booster in late March for people over the age of 50 with a healthy immune system.
Authorities said the vaccine was 80% effective against Covid hospitalization at least one week after the fourth dose. This was a significant increase from the 55% efficacy provided by the three doses after 4 months in that age group.
It was not clear how quickly the protection provided by that fourth dose diminished. The study also did not measure the performance of the vaccine against the latest Omicron subvariant, BA.5. This seems to be driving a new surge in cases and hospitalizations. Its subvarieties have become dominant in new cases in the United States and appear to be the most evasive form of Omicron spreading domestically.
As hospitalizations increase, federal health authorities urge qualified people to receive boosters as soon as possible, and these injections do not prevent additional doses of mutant-specific vaccines updated in the fall or winter. Said. The latest results have strengthened the need for booster shots, the agency said.
The CDC said on Friday, “Given the recent increase in deaths and hospitalizations associated with the BA.5 variant, the recommended Covid- includes additional booster doses for people with moderate to severe immunodeficiency. 19 Vaccination must be kept up-to-date. Adults over 50 years. “