Vaccine protection against moderate illness waned among adolescents, new C.D.C. data suggest.

Five months after immunization, two doses of the Pfizer-BioNTech vaccine appeared to provide little or no protection against moderate disease caused by the Omicron variant, as measured by visits to emergency departments and emergency clinics among adolescents aged 12 to 17 years. Data published on Tuesday Centers for Disease Control and Prevention.

But booster shots dramatically increased protection, supporting the agency’s recommendation to boost everyone 12 years of age and older.

The findings should be interpreted with caution. The agency’s study did not exclude unvaccinated teenagers who had some immunity from prior infection, which could make the vaccination seem less effective than it actually was.

And the researchers offered only limited data on hospitalizations, which is a more reliable proxy for severe illness than emergency room visits and emergency room visits.

“One of the limitations of this data is that parents may take their children to the emergency room or the emergency room for a variety of reasons, and the effectiveness of the vaccine depending on the immunodeficiency state, the underlying health condition, or the vaccine product has not yet been studied,” the CDC said. In a statement.

Several studies have shown that although the effectiveness of the vaccine against infection wanes over time, the immune response remains highly protective against hospitalization and death, even against the highly contagious Omicron variant.

A separate analysis of data from 29 jurisdictions posted on the CDC website reported nine Covid-related deaths among vaccinated children and adolescents aged 5 to 17 between early April 2021 and January 2022 compared to 121 deaths among unvaccinated children of the same age.

However, the findings suggest that scientists should carefully monitor the effectiveness of the vaccine in children and adolescents over time, keeping in mind that boosters may be needed.

“We need to see more studies like this to see if this is true,” said Deepta Bhattacharya, an immunologist at the University of Arizona. “But I think it’s likely, and as parents, we should be prepared for it to be another try.”

The results are of particular importance to parents as school districts across the country are considering ending mandatory mask-wearing. The CDC released new guidance last week that says about 70 percent of Americans can safely drop masks in public spaces.

Distribution of the vaccine to young children has been slow; less than one in four children aged 5 to 11 are currently fully vaccinated. More than half of adolescents aged 12 to 17 were fully vaccinated with two shots, and about 12 percent received a third booster dose.

The findings follow data released on Monday, which show two doses provide little protection against Omicron variant infection in children aged 5 to 11 years after just one month. The vaccine has been shown to provide less protection against infection even in adults, especially against the Omicron variant. New data published by CDC reflect this trend on their website.

In the new study, researchers analyzed data from 39,217 emergency room and emergency room visits and 1,699 hospital admissions for children ages 5 to 17 in 10 states from April 9, 2021, to January 29, 2022.

Coronavirus pandemic: what you need to know

New US strategy. The White House has unveiled a virus response strategy that aims for a “new normal,” but much of it will require congressional funding. The plan includes a “test for cure” initiative that will provide antivirals to patients as soon as they know they are infected.

Vaccination of adolescents. Five months after immunization, two doses of the Pfizer vaccine appear to offer little or no protection against moderate Omicron disease in adolescents aged 12 to 17, according to new data from the US Centers for Disease Control and Prevention. However, booster shots dramatically increased protection.

In children aged 5 to 11 years, the vaccine’s ability to prevent moderate disease decreased to 46 percent about two months after full vaccination (two weeks after the second shot). Most visits to emergency rooms and emergency clinics occurred during the Omicron surge, when older children and adults were also more vulnerable than previously during the pandemic.

Vaccine efficacy against moderate illness in adolescents remained stable during the Delta era. But 150 days after the full vaccination, the effectiveness plummeted to 38 percent in teens aged 12 to 15 and to 46 percent in teens aged 16 and 17.

When the researchers analyzed the data specifically for protection in the Omicron era, protection against moderate disease virtually disappeared in adolescents who were vaccinated more than 150 days ago. But the third dose of the vaccine restored the effectiveness to 81 percent.

The results are consistent with those in adult studies showing that the effectiveness of the vaccine against infections and minor illnesses declined sharply over time, especially after the introduction of the Omicron variant.

Efficacy is a comparison of protection in vaccinated and unvaccinated groups of people. But as more of the population becomes immune through infection, it’s getting harder to get a true picture of a vaccine’s effectiveness, said Paul Offit, director of the Philadelphia Children’s Hospital Vaccine Education Center and advisor to the Food and Drug Administration.

“Are we comparing apples to apples when we say the effectiveness of a vaccine is declining?” he said.

The defense against severe illness was even more difficult to decipher. In younger children, there were too few hospitalizations to draw firm conclusions. Among adolescents who were vaccinated more than 150 days ago, efficacy against severe disease remained high, at 70 percent or higher.

But the majority of these hospitalizations occurred during the Delta era, so the data does not provide insight into effectiveness against hospitalizations as the Omicron variant emerges and spreads.

The CDC recommends booster shots for Americans 12 years of age and older. Pfizer and BioNTech are evaluating the benefits of the third dose in young children.

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