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Everything you ought to know about the flu

October 20, 2010 2 comments

Well, not exactly everything, but a lot.

What is “the flu”?

Influenza, or “the flu” is an extremely contagious respiratory illness caused by influenza A or B viruses. Flu appears most frequently in winter and early spring. The flu virus attacks the body by spreading through the upper and/or lower respiratory tract. There are 3 types of flu viruses, A, B and C which can cause the flu, and new strains (especially the A type) evolve every few years.

Type A viruses are responsible for major flu epidemics every few years. Type B is less common and generally results in milder cases of flu. However, major flu epidemics can occur with type B every three to five years. There is a third type of virus, C, which also can infect but does not produce flu symptoms.

What are the symptoms/effects of the flu?

Besides generally making one feel miserable, here is a list of some of the most typical flu symptoms/effects.

  • Headaches
  • Severe aches and pains in the joints and muscles and around the eyes
  • Cough
  • Respiratory congestion
  • Fever
  • Chills
  • Fatigue & exhaustion
  • Severe flu can lead to pneumonia
  • Sore throat and watery discharge from your nose

Are there any complications that can arise from the flu?

The most common flu complications include viral or bacterial pneumonia, muscle inflammation, and infections of the central nervous system or the sac around the heart. Other flu complications may include ear infections, sinus infections, dehydration, and worsening of chronic medical conditions, such as congestive heart failure, asthma, or diabetes.

Those at highest risk for flu complications include adults over 50, children ages 6 months to 4 years, nursing home residents, adults and children with heart or lung disease, people with compromised immune systems (including people with HIV/AIDS), and pregnant women.

How does flu spread?

The flu is spread from person to person through respiratory secretions and typically sweeps through large groups of people who spend time in close contact, such as in daycare facilities, school classrooms, college dormitories, military barracks, offices, and nursing homes.

Flu is spread when a person inhales droplets in the air that contain the flu virus, make direct contact with respiratory secretions through sharing drinks or utensils, or handle items contaminated by an infected person. In the latter case, the flu virus on your skin infects you when you touch or rub your eyes, nose, or mouth. That’s why frequent and thorough hand washing is a key way to limit the spread of influenza. Flu symptoms start to develop from one to four days after infection with the virus.

Will one catch the flu if one goes out in the cold or gets wet by cold rain?

No. The flu is a viral infection; you need to come in contact with the flu virus to get infected. Feeling cold or being wet does not give you the flu. It might give you a runny nose though and other symptoms that may be reminiscent of the flu, but it does not cause a flu infection.

What are the symptoms/effects of the flu vaccine?

The most common side effects of the flu vaccine (both inactivated and LAIV) include mild:

  • Swelling at the site of the injection (inactivated only)
  • Headache
  • Cough
  • Body ache
  • Fever

When should one get the flu vaccine?

As soon as it is available.

How many types of flu vaccines are there?

There are two types of flu vaccine. Inactivated and LAIV. The inactivated vaccine is given as a shot, generally in the arm, while the LAIV version is a nasal spray. The main difference between the two is that the inactivated, or the shot, contains dead viruses, whereas the LAIV version contains alive, but extremely weakened, viruses. Because of that, the spray is expected to be more effective in inducing an immune reaction than the shot.

Why is the flu vaccine different every year?

Two of the three flu viruses are responsible for causing flu, type A and type B. Type A has 16 subtypes, while Type B is not categorized by subtypes.  They both can mutate, especially type A which results in new strains every few years. Every given year, any combination of various strains of the various subtypes of A and of Type B can be in circulation and causing flu.

Every given year, both the LAIV and Inactivated vaccine contain three strains of influenza virus that are chosen each year based on what scientists predict will be the circulating viruses for the flu season. Given the long production times, it is impossible to know for sure which strains will be prevalent in the upcoming season, so every year scientists have to do their best to predict what they think will be the prevalent strains. Usually this process is done months ahead of the actual flu season. This is why the flu vaccine is different each year, and why we have to get re-vaccinated each year.

Which strains does the 2010 vaccine protect against?

Every year, the flu vaccine, protects against 3 specific strains of viruses that cause flu. The 2010 vaccine protects against two A viruses and one B virus. This year the vaccine protects against these 3 strains:

  • an A/California/7/2009 (H1N1)–like virus (Swine Flu)
  • an A/Perth/16/2009 (H3N2)–like virus
  • and a B/Brisbane/60/2008–like virus

Can you get the flu from the flu vaccine?

No! You cannot get the flu from the flu vaccine. You may, however, experience some flu-like symptoms, which can be experienced from any vaccine in some cases and doesn’t have anything to do with the actual disease you’re being inoculated against.

How effective is the flu vaccine?

The effectiveness of the flu vaccine depends on the strains in circulation and the strains the vaccine prevents from. When the vaccine viruses and circulating viruses are well-matched, the vaccine can reduce the chances of getting the flu by 70% to 90% in healthy adults.

Can you get the flu, even if you get vaccinated?

Yes. Firstly, as we already saw, the 3 strains in the flu vaccine have to be guessed in advance of the flu season. If there is a good match between the predicted strains and the actual strains in circulation, the vaccine will provide good protection. On the other hand, even if there is a perfect match, no vaccine is 100% effective, so even then a person who got vaccinated may still develop the flu. However, in general, people who are vaccinated experience milder symptoms than the non-vaccinated ones.

Who should get the flu vaccine?

Except for high risk groups that are advised to skip the vaccine, it is recommended that everyone over 6 months of age should get the flu vaccine.

Who should not get the flu vaccine?

Anyone with a severe allergy to eggs or egg products should not get a flu shot. Other people who should not get a flu shot include:

  • Infants under 6 months old.
  • Anyone who has had a severe reaction to a past flu shot or nasal spray.
  • Someone with Guillain-Barre syndrome.
  • People with moderate to severe illness with a fever; they should be vaccinated after they have recovered.

How Long Am I Contagious After I Get the Flu?

You are contagious for up to seven days after the onset of the flu, although the flu virus can be detected in secretions up to 24 hours before the onset of symptoms. This means you might transmit the flu virus a full day before your flu symptoms begin.

In young children, the flu virus can still be spread in the secretions even into the second week of illness.

How Can I Prevent the Flu?

To prevent the flu, be sure to keep your hands clean — making sure to wash them frequently to remove germs — and get a flu shot. The CDC develops a flu vaccine based on the type A strain that they believe will be most prevalent in the coming flu season. This is the vaccine you get with the annual flu shot or FluMist nasal spray.

Give me some statistics please?

-Every year during flu season, 1 in 20 Americans will contract the disease. Some years incidence can be as high as 1/5.

-Annually there are about 200,000 hospitalizations and an average of 23,600 annual deaths from the flu  in the US alone.


Sources

WebMD

Flu.gov

CDC Flu Website

World Health Organization Influenza Page

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European Medicines Agency finds no link between swine flu vaccine and narcolepsy

September 23, 2010 2 comments

The European Medicines Agency, a decentralised agency of the European Union, located in London, which is responsible for the scientific evaluation of medicines developed by pharmaceutical companies for use in the European Union, reports through a press release dated 09/23/10, that after reviewing all the available data and reports on the supposed link between the swine flu vaccine, Pandemrix, and the sleeping disorder of narcolepsy, that “the available evidence was insufficient to determine whether there is any link between Pandemrix and reports of narcolepsy, and that further studies were necessary to fully understand this issue.

Pandemrix was used in Europe during the 2009 H1N1 influenza pandemic, at which time up to 30 Millions Europeans received the vaccine. This year, up to September 17, 2010, 81 reports suggestive of a connection between the vaccine and narcolepsy were collected. The Committee maintains that so far the risk-benefit of the vaccine is still positive and no restrictions in use are necessary.

It is important to keep in mind however, that the EMA Committee is not saying that there is no connection between Pandemrix and narcolepsy, but only that the current evidence is insufficient to establish a causal relationship between the two.  They caution that more research is needed to reach solid conclusions. In fact, they are continuing the analysis and review of the reports received.

The ongoing review is complex and will take some three to six months to complete. The Agency is working with experts from across the European Union to carefully scrutinise all available reports. Owing to a potential overlap of narcolepsy symptoms with several other neurological and psychiatric disorders, diagnosis is very often not confirmed until several years after symptom onset.

The number of reports of narcolepsy that occurred in children in some countries seems to be higher than expected in comparison with data from previous years. However, there are many uncertainties in the available information that need to be clarified. These include a possibility that earlier diagnoses of narcolepsy have contributed to this apparent increase. Also, the influenza pandemic itself may have contributed to a change in the rates of narcolepsy. These factors need to be assessed before firm conclusions can be drawn.

The ongoing review will require new observational (epidemiological) research in order to reach any firm conclusions on whether there is a link between Pandemrix and narcolepsy.

CDC releases preliminary data on 2009 H1N1 vaccine and Guillain-Barre Syndrome

June 4, 2010 4 comments

As part of its Morbidity and Mortality Weekly Report (MMWR), the Centers for Disease Control and Prevention (CDC) has released a report titled “Preliminary Results: Surveillance for Guillain-Barré Syndrome After Receipt of Influenza A (H1N1) 2009 Monovalent Vaccine — United States, 2009–2010“.  This publication reports on an analysis of preliminary data, the focus of which was to look for any signs of increased risk of GBS rates among individuals receiving the 2009 monovalent H1N1 vaccine in the United States.

Guillain-Barre Syndrome is a rare neurological disorder (affecting about 1.65 and 1.79  in 100,000)  in which the body’s immune system attacks part of the peripheral nervous system. On some occasions, it has been  identified to be triggered by surgery or vaccination. For example, as has been widely reported, especially by the anti-vaccination crowd, the 1976 influenza A (H1N1) vaccine was associated with a statistically significant increased risk for GBS of over 10 cases per million, and it appears that some vaccines may account for a slight overall increase in GBS risk.

Given the history with the 1976 H1N1 vaccine, the CDC has been closely monitoring the 2009 H1N1 vaccines, through its Emerging Infections Program (EIP) since October 2009.  Preliminary results of this analysis show an excess of 0.8 cases of GBS for 1,000,000 vaccinations, similar to the rate for seasonal influenza vaccines. If this holds up when the full review is released some time in the Fall of 2010, it would mean that the 2009 H1N1 vaccine will be associated with an 8% increase over the expected GBS rate of 1 in 100,000.

To put things in perspective, while the H1N1 vaccine may be associated with less than 1 additional case of GBS per million vaccines, the disease it protects from, H1N1 influenza has been associated with 9.7 deaths per million. According to Wikipedia, 80% of GBS patients recover fully, which means that of the 0.8 additional cases per million vaccination, only about 0.16 will have permanent effects (including paralysis and death). To put this further into perspective, if this association holds, we should expect about 16 cases of additional GBS with permanent side effects, for every 100,000,000 vaccinations. At the same time the death rate from influenza A (H1N1) would be at about 970. And if that is not enough perspective, according to this study, the mortality rate, at least for the period 2000-2004 was at 2.58 %, whereas Wikipedia estimates overall mortality rate to be at around 4%. Using the larger number, the 4% from Wikipedia, if the association holds at the same level, we would expect an additional 3.2 vaccine induced GBS deaths versus 970 influenza H1N1 deaths, per 100 million people.

Even if the H1N1 vaccine is only 50% effective in preventing H1N1 influenza, that’s still  485 saved lives vs. 3.2 additional deaths.  This overwhelmingly shows that vaccinating for influenza A (H1N1) is to be highly preferred vs. not vaccinating, since the chances of any one person dying from influenza would be about 151 times higher than dying from vaccine induced GBS. To put it differently, every person that chooses not to vaccinate for H1N1 out of fear of dying of vaccine induced GBS, is effectively choosing to take a risk of dying from the disease 151 times higher than the one they are afraid of (and this is only at an assumed 50% vaccine efficacy rate)! That is kind of like preferring to jump out of the 10th floor of a building because you’re afraid you may break your leg jumping out of the first floor window.