The flu vaccine may be less effective this year, according to a new CDC report

The effectiveness The number of influenza vaccines this year in South America was lower than last season, the Centers for Disease Control and Prevention reported Thursday, which could be an indication of the level of protection Shots could offer something to the people of the US this winter.

According to preliminary estimates from a new article published in the CDC’s Morbidity and Mortality Weekly Report, the vaccine’s effectiveness against hospitalization was 34.5% in high-risk groups such as young children, people with underlying medical conditions and older adults. This means that vaccinated people in these groups were 34.5% less likely to get sick enough to require hospitalization than unvaccinated people.

Last year, the CDC report estimated the vaccine’s effectiveness in South America at 51.9% against hospitalizations among at-risk groups. A study by the same group that examined data from 2013 to 2017 estimated effectiveness at about 43% for fully vaccinated young children and 41% for older adults.

This data comes from a research network coordinated by the Pan American Health Organization and includes Argentina, Brazil, Chile, Paraguay and Uruguay.

The biggest drop in effectiveness this year may be due to fewer cases of “A(H1N1)pdm09,” a strain that has spread since the H1N1 swine flu pandemic in 2009.

In the past, flu vaccines have generally shown better effectiveness against H1N1 than against H3N2.

While H1N1 dominated almost all infections in South America last year, the World Health Organization said this year there was more evidence of the flu subtype H3N2.

If there are similar patterns of flu virus strains in the Northern Hemisphere, the study authors write that “health authorities may expect similar levels of protection.”

A CDC spokesman said the vaccine’s effectiveness against H1N1 was “in line” with previous seasons.

“Overall, flu vaccination reduced the risk of hospitalization by about a third, which would have a significant impact on the burden of disease. Receiving a flu vaccination can provide significant protection against serious outcomes,” CDC spokesman David Daigle said in an email.

U.S. officials often look to Southern Hemisphere countries to preview how this year’s flu season will unfold, as winter there falls into the Northern Hemisphere’s summer.

The CDC said in August that the Southern Hemisphere’s flu season this year was “similar to previous flu seasons,” but also pointed to unusually high hospitalizations for severe flu from Chile, Ecuador and Uruguay.