Limited effect of flu vaccines

Effect of flu vaccines very different

08/12/2014

Experts believe that this year's flu season is particularly difficult. The first results suggest, as the American disease agency Centers for Disease Control and Prevention (CDC) announced in a press release. The CDC therefore recommends promptly a vaccine for prevention and immediate treatment with specific drugs in high-risk patients.

In the course of this year's season, the A H3N2 virus variant was the most widespread. It is a very aggressive virus, „which causes more severe flu illnesses, hospitalizations and deaths.“ For example, in the years 2012/2013, 2007/2008 and 2003/2004, in which the H3N2 virus predominated, the three flu seasons were the highest with mortality rates.
What increases the risk of a severe flu season is the realization that the viruses found in blood tests are mutated versions that are not covered by the flu vaccine. This means that the effectiveness against the mutants is reduced. Currently, in the case of the H3N2 mutant, a 37-42 percent efficiency is assumed.

„It's too early to say for sure that it's going to be a heavy flu season, but Americans should be prepared“, Tom Frieden, director of the CDC. "We can save lives with a three-point plan to combat influenza: vaccination, immediate treatment for people at high risk for complications, and preventive health measures like staying home when you're sick to reduce the spread of the flu. "

Typically, flu vaccines are effective against 3 to 4 viral variants, even if they are only partially effective against some.

„Although the efficacy of the H3N2 influenza vaccine is limited this year, we still strongly recommend that you be vaccinated“, said Joseph Bresee, M.D. of the CDC. „As has been shown in recent years, the vaccine offers some protection against mutated virus strains. In addition, they help to protect against later in the season, other influenza virus strains.“

The main cause of the problem is the fact that the virus strains change regularly. However, as the vaccines have to be produced in advance, it is important for producers to estimate in advance of the flu season which viral strains will predominate in the season. If they change then this can reduce the effectiveness of the vaccine. Since H3N2 was predominant in the southern hemisphere in recent years, it was assumed in February that this virus would also dominate in the northern hemisphere during the flu season. Accordingly, vaccine manufacturers have produced vaccines against this strain on the recommendation of WHO. However, as it turns out now, a related strain of H3N2 is spreading, against which the vaccine is only partially effective. According to the Robert Koch Institute, such developments have already occurred in the past, and it is assumed that they can be expected in the future as well. After all, the race with the virus is one in which one has to be lucky enough to win it: the luck to make the right decision in the spring for the following autumn. (Jp)