It’s Not Too Late for Flu Vaccination

Flu vaccine effective against influenza A and B including H1N1

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) This year’s flu vaccine provides protection against the most common strain of flu this year, H1N1. The flu is still infecting people, and it’s not too late to get vaccinated.

Each year, the Centers for Disease Control and Prevention (CDC) estimates the effectiveness of the seasonal flu vaccine. The interim report has just been released.

The report showed that the flu vaccine was effective at protecting against the flu in the majority of cases.

Nearly all cases of flu this year have been an H1N1 strain that is similar to the virus that caused the flu outbreak in 2009.

"Talk to your doctor about the flu vaccine."

This interim report from CDC was written by Brendan Flannery, PhD, from the Influenza Division of the National Center for Immunization and Respiratory Diseases at the CDC, and a team of experts.

To assess the effectiveness of the vaccine, these researchers enrolled adults and children at five different sites around the United States between December 2, 2013 and January 23, 2014. A total of 2,319 people were enrolled.

Patients were enrolled if they were 6 months old or older, reported that they had an acute respiratory illness with cough that started at least seven days earlier and had not been treated with antiviral medications.

The researchers noted whether the patients had been vaccinated at least 14 days before they became ill.

Nasal swabs were taken so that the researchers could test for the presence of the flu virus and, if present, determine what kind of flu virus it was.

The flu virus was found in 34 percent of the patients, and 99 percent of the viruses detected were influenza A. A total of 98 percent of the influenza A viruses were H1N1.

Of the people who had the flu virus, 29 percent had been vaccinated. Half of the people who did not have the flu virus had been vaccinated.

From these results, the research team calculated that the flu vaccine was 61 percent effective against the flu and 62 percent effective against H1N1.

“[E]arly estimates for the 2013-14 season indicated that as of mid-November, only 34 percent of adults aged 18-64 years had received the influenza vaccine this season, compared with 41 percent of children and 62 percent of adults aged [65 years or older],” wrote Dr. Flannery and team.

“Influenza activity is likely to continue for several more weeks in the United States. Vaccination efforts should continue as long as influenza viruses are circulating,” these researchers recommended.

Dr. Flannery and colleagues noted several limitations of their study. These limitations included the fact that participants self-reported if they were vaccinated and not all vaccinations were verified by the time the report was written. Some participants may have needed additional vaccinations for virus protection, as children under age 9 need two vaccinations, and rates of flu infection may be different at the end of the flu season than they were at the time of this study.

This interim report was published in the February 21 issue of the CDC's Morbidity and Mortality Weekly Report.

Review Date: 
February 27, 2014
Last Updated:
March 1, 2014