H1N1 flu (swine): symptoms, contagion, treatments, vaccine

The H1N1 flu , also known as swine flu or influenza A, is a variation of the common flu and is generally more severe.

With the history of outbreaks that occurred in Brazil in previous years and the recent cases of deaths from the disease, public health agencies annually issue a warning for the prevention and vaccination of populations at risk.

In the following text, we explain what this type of flu is and how to stay protected.

What is H1N1 flu?

The H1N1 flu (influenza A or swine flu) is caused by a subtype of the Influenza A virus, H1N1, a mutation of the virus stronger than that of the common flu . Due to the pandemic it caused in 2009, it is one of the most worrying strains.

This flu is transmitted in the same way as the common flu, but its symptoms are stronger, sudden and, if not treated early on, can lead to more serious complications and even death.

Despite being a disease with great potential for transmission, it can be prevented through some habits and mainly through the vaccine.

For this, there is the trivalent and quadrivalent vaccine, which offer protection against different flu subtypes, including H1N1.

The priority groups for vaccination are children over the age of 6 months to less than 6 years, the elderly, pregnant women, women in the puerperium, health workers, teachers, indigenous people, the population deprived of their liberty and employees of the prison system.

In 2019, until March, 145 confirmed cases of people with severe acute respiratory syndrome due to infection with the H1N1 virus were recorded. Within this number of cases, 110 were registered in the state of Amazonas. There, the flu has been responsible for 28 deaths.

The campaign, anticipated this year on account of these numbers, takes place between April 10 and May 23.

How did the H1N1 flu come about?

The disease was first detected worldwide in the 1919 pandemic, and since then, the causative virus has acted as a seasonal flu virus.

The main cases of H1N1 influenza in people were discovered in Mexico in 2008. Scientifically, the Influenza A virus was already known to affect pigs, but in humans it was the first time that it happened, through a mutation of the same virus, now known as H1N1.

H1N1 outbreaks in the world

Like seasonal flu, H1N1 flu can range from mild to severe in terms of intensity. From 2005 to 2009 there were only 12 cases of the disease in the United States, but in the years 2009 and 2010 there was an extremely serious pandemic.

2009/2010 pandemic

The global outbreak began in Mexico in 2009, later expanding to North America, Europe and Oceania.

In April of that same year, the World Health Organization (WHO) declared that the epidemic was an “international public health emergency”, that is, all countries on the planet were subject to disease.

The H1N1 flu was, on a scale of 1 to 6 of the WHO alert, on scale 6, defining it as a pandemic worldwide. In 2010, Brazil had more than 58 thousand cases of the disease and 2,100 confirmed deaths.

Outbreak 2016

Despite the flu being a winter illness, the H1N1 flu arrived earlier in 2016 here in Brazil and was responsible for half of the flu cases in the country. In early April of the same year, 15 states were found to have confirmed cases of H1N1 flu and the largest flow is in the Southeast region only in São Paulo, they exceed 80% of the entire country.

Some cases of the disease were confirmed already in the summer and it is believed that the cause of this advance is the climatic condition caused by the El Niño phenomenon.

Difference between H1N1 and H3N2

H3N2 and H1N1 are subtypes of the Influenza A virus, being the most prevalent in cases of the disease. In previous years, when there were reports of flu outbreaks, the cause was significantly caused by the H1N1 subtype.

Recently, the picture has changed and the number of cases of the disease has become much higher due to the H3N2 subtype. However, despite the numerous variations that these viruses can suffer, both are capable of causing major epidemics and deaths.

Therefore, the only difference is that they belong to different strains, that is, viruses of different strains that descend from the same type, in which they share morphological or physiological similarities.

Causes: the Influenza A virus

Swine flu is caused by the influenza virus, subtype A. Influenza A viruses, the etiological agent of Myxovirus influenzae , are the only ones capable of causing frequent annual epidemics and, to a lesser extent, pandemics.

They are able to reach all age groups in a short period of time, a characteristic possible due to their great power of variability and adaptation.

Because it has genetic material of a fragmented nature, the virus undergoes several mutations during the replication phase. In this process, the surface proteins (hemagglutinin and neuraminidase) are modified.

The mutations that the influenza virus undergoes happen independently. As a consequence, a variant of the virus can pass through the population and cause the disease, since immunity is not prepared for a new strain.

How does the transmission happen?

The H1N1 flu, as well as the common flu, can be transmitted through contact with contaminated objects, respiratory droplets in the air and contact with the saliva of someone who has the virus. This contact can happen in two ways:

  • Direct transmission : happens from person to person, through contact with saliva droplets through speech, sneezing or coughing.
  • Indirect transmission : after the hands come into contact with some contaminated surface, the virus is introduced into the body by touching the eyes, mouths and nose. Household items or public places can easily become contaminated with traces of the flu virus, including food, door handles, remote controls, handrails, telephone sets and computer keyboards.

The transmission period varies according to some conditions. Adults, for example, can transmit the virus up to 24h to 48h before the onset of symptoms.

Contrary to what many people think, there is no risk of being infected with the disease through pork , as according to the World Health Organization (WHO) and the Center for Disease Control and Prevention (CDC), the virus it is transmitted only from people to people.

What are the risk groups?

Some people are at higher risk of complications. They are:

  • People from 60 years old;
  • Pregnant women from 12 weeks;
  • Mothers up to 45 days postpartum;
  • Children from 6 months to 5 years;
  • People with chronic non-communicable diseases;
  • Health workers;
  • Indigenous population;
  • People with diseases that increase the risk of complications due to influenza;
  • People deprived of their liberty.

To this select group, the public and private health systems offer the vaccine to prevent the H1N1 flu.

Symptoms of the H1N1 flu

The symptoms of H1N1 are similar to those of the common flu, such as fever , tiredness , body aches, sneezing and coughing .

Fever and chills

In the H1N1 flu, patients have a high fever, above 38ºC. Fever is a common symptom in these conditions, as it is a response by the body in an attempt to fight viral infection.

In this condition, the patient may also experience chills, an involuntary tremor that causes the muscles to contract.

Pain in the body, throat and head

It is common that in a flu-like condition the patient has muscle pain and headache. Although the infection especially affects the patient’s respiratory tract, the whole organism is weakened by the disease, which is why this sensation of generalized pain.

Dry cough and sneezing

Coughing and sneezing are natural responses of the respiratory system when some microorganism invades our body. That is why patients with the flu have these symptoms, being quite characteristic within the framework.

Fatigue or tiredness

Also as a consequence of all the associated symptoms, the H1N1 flu also causes tiredness in patients. Unlike a common cold or flu , in these cases people are more debilitated, which may require a longer rest period.

Other symptoms

In addition to these symptoms, it is also possible that diarrhea and vomiting may also occur in the infected person, but these are not as recurrent as those reported above.

The recommendation is that, when you notice the frequency of these symptoms, or at least some of them, you should seek medical help to undergo a clinical examination and thus be sure of the diagnosis.

What is the difference between the symptoms of H1N1 and a common flu?

The symptoms of common flu and H1N1 are similar, but with different intensity. In common, high fever, headache , body pain, coughing, chills and sneezing can occur . In H1N1, in addition to these, you may also experience diarrhea, vomiting, shortness of breath and appetite.

Due to its sudden and accelerated evolution, if the H1N1 flu is not properly treated it can cause serious complications, such as pneumonia , respiratory distress and, in even more severe cases, death.


The diagnosis of the flu can be made by a general practitioner, but also by specialists in the areas of infectious diseases and pneumology. In addition to analyzing the symptoms presented by the patient, to confirm the diagnosis the doctor may also need to perform some laboratory tests.

It is common to have an analysis of the secretion of the nasopharynx, which can be done even during the onset of the disease, within the first three days since the appearance of the flu signs and symptoms.

Is there a cure?

-Yeah . The flu caused by the H1N1 virus, like other flu types, is curable. With treatment, the patient usually remits within seven days, but it can take up to two weeks for the patient to be completely infection-free.

However, because it is caused by a virus that can mutate, it is possible that a person who has had the flu and is cured may have relapses of the disease.

To prevent this from happening, it is important to prevent yourself with the vaccine.

Treatment of H1N1 flu

Treatment is based on the use of antiviral drugs with the active ingredients Zanamivir and Oseltamivir Phosphate , known by the trade names Tamiflu or Relenza . They are drugs that show good results when the use is started in the first 48 hours of the disease.

The use of medications is done with a medical prescription, after medical diagnosis. In addition to antivirals, other medications may be needed to relieve symptoms, such as antipyretics, pain relievers and expectorants.

Another part of the treatment, which is up to the patient, is to maintain good hydration and rest.


NEVER self-medicate or stop using a medication without first consulting a doctor. Only he will be able to tell which medication, dosage and duration of treatment is the most suitable for his specific case. The information contained on this site is only intended to inform, not in any way intended to replace the guidance of a specialist or serve as a recommendation for any type of treatment. Always follow the instructions on the package insert and, if symptoms persist, seek medical or pharmaceutical advice.

Home treatments

There are no miracle homemade recipes that cure the H1N1 flu, but there are some precautions that help make treatment more comfortable. Some foods can also help to strengthen immunity and help the body to recover more quickly from the disease.


There are some teas that help strengthen the immune system, help relieve vomiting, headaches and improve breathing. In addition to drug treatment, they can be another reinforcement against the flu.

Some tea options are garlic, echinacea, chamomile, eucalyptus, ginger and propolis tea .

Read more:  What is garlic tea for?


Maintaining food at any time is always welcome. But, when we are sick, it is even more important.

To help our body defend itself against infection, it is essential to consume nutritious foods, such as fruits and vegetables. Some options to include in your diet include plain yogurt, salmon, orange and dark green leafy vegetables.

H1N1 flu vaccine

There is no specific vaccine for H1N1 flu. The existing flu vaccine is capable of protecting against Influenza A (which includes the H1N1 subtype) and B viruses . This vaccine can be trivalent or tetravalent.

The trivalent vaccine is the one made available by the public health system to groups at risk, but it can also be purchased at private vaccination clinics.

This vaccine is able to protect people against Influenza A subtypes (H1N1 and H3N2) and against an Influenza B subtype.

The quadrivalent, however, has the difference of protecting against two subtypes of Influenza B, being available only in private clinics.

It is not a vaccine distributed in SUS, because the extra strain in which it offers protection does not have significant circulation in the country, so immunization is not mandatory.

Who should take it?

All people can receive the vaccine, but for groups at risk, it becomes indispensable. According to the Ministry of Health, the following groups should be prioritized:

  • Children from 6 months to 5 years of age;
  • People over the age of 60;
  • Pregnant women;
  • Health workers (doctors, nurses, hospital receptionists, security guards, etc.);
  • Indian people;
  • Postpartum women (up to 45 days after delivery);
  • Prison system officials;
  • Prison population;
  • Public or private network teachers;
  • People who have any clinical condition or chronic non-communicable disease (diabetes, obesity, transplant, kidney, liver or heart disease, patients with trisomies).

Side effects

The possible side effects of the vaccine are divided into two types: local and systemic. They include the following symptoms:

  • Pain at the site;
  • Redness of the skin (erythema);
  • Fever;
  • Discomfort;
  • Muscle aches;
  • Hypersensitivity reactions.

Local manifestations, such as pain at the site and redness, are signs considered benign. It happens between 15% to 20% of patients and tends to disappear within 48 hours after application.

Signs such as fever and malaise, identified as systemic reactions, can occur between 6 hours to 12 hours after the vaccine and remain for up to 2 days.

Within that time, if the symptoms do not improve, the patient should seek medical advice. They are not common side effects, being recurrent in 1% of patients who receive them, usually when referring to the first contact with the vaccine.


The influenza vaccine had the contraindication to be avoided by people with a history of severe allergy to egg protein.

However, according to new recommendations from the Center for Disease Control (CDC) and the Advisory Committee on Immunization Practices (ACIP) in the USA, it is possible that these people will be vaccinated.

These guidelines, proposed in 2016, pose certain conditions for allergy sufferers to receive vaccination safely.

  • People allergic to egg protein who have urticaria can receive the influenza vaccine, without any attention different from that of other patients;
  • People allergic to egg protein who have symptoms other than urticaria, such as dizziness, frequent vomiting, angioedema, difficulty breathing, who may need adrenaline or any type of emergency medical intervention, can receive the vaccine as long as it is applied in a hospital, with medical supervision available.

With these new recommendations, it appears that it is no longer necessary for people allergic to the egg to remain for 30 minutes in observation, as in the old procedure.

However, as is recommended for all types of injectable vaccines, which can cause dizziness in the patient, all people must remain under observation for 15 minutes, until they are released.

People who have an allergic reaction when receiving the first dose are also considered within the group of contraindications and should not receive the vaccine again.

Therefore, it is worth remembering that even with the new review on vaccination for egg allergies, it is necessary to be careful and correctly follow the entire procedure.

The vaccine should also not be applied to children under 6 months of age .

Vaccination campaign

The National Flu Vaccination Campaign is promoted annually by the Ministry of Health to raise awareness and alert about the importance of immunization in groups at risk and in the population in general.

20 editions of the campaign have already been promoted and in 2019 the 21st edition will take place. In 2018, the campaign took place from April 23 to June 1, with the aim of vaccinating more than 54 million people who belong to high-risk groups free of charge.

In 2019 it will be a little different. The campaign was anticipated to help reduce the number of deaths already registered due to infection with the H1N1 virus.

For this reason, this year, the campaign takes place between April 10 and May 31 , with the national mobilization day (D-day) scheduled for May 4.

Read more: ANVISA approves new flu vaccines for 2019 campaign

Complications: can H1N1 flu kill?

Unfortunately, yes . The disease can progress to more severe conditions when there is no adequate treatment or when the disease affects patients with already compromised clinical condition.

Therefore, in some cases, the H1N1 flu can lead the patient to death.

The most common complications in flu patients include other infections and aggravated chronic illnesses. Understand:

Aggravated chronic diseases

The flu can lead the patient who already has a chronic illness to a worsening of his health condition that he already suffered before viral infection, such as patients who have heart failure, asthma and diabetes .


The H1N1 flu patient is more vulnerable to complications such as pneumonia, whether viral or bacterial. This is because your body is more weakened, which increases the risk of other infections.

It is a serious condition, because in the disease the health of the lungs is compromised, causing respiratory failure, chest pain , malaise, fever and other symptoms.


It is an inflammation that affects the heart muscle, the myocardium. It is an indispensable muscle because it is responsible for the contraction movement of the heart. When it is not working perfectly, the pumping of blood to the whole organism is impaired. It can therefore cause arrhythmia and heart failure;


The encephalitis is an acute inflammation that affects the brain, which may be caused by viral infections. It is a rarer complication, but it can affect people with weakened immune systems.


The meningitis is an inflammation that occurs in the meninges, the membranes surrounding the brain and protect the central nervous system. It is a serious disease that happens for several causes, viral infection being one of them.

How can I prevent myself?

In addition to receiving the vaccination annually, other tips are important for you to add to your day to day:

  • Drink plenty of water, so that there is no accumulation of secretion;
  • Always wash your hands with soap and water and avoid placing them on your face and, especially, in the mouth area;
  • If you can’t wash your hands, carry a bottle of gel alcohol in your bag to sterilize them;
  • Do not share personal items, such as cutlery, towels and glasses;
  • Avoid close contact with someone infected;
  • Avoid going to places that are closed and with a lot of people;
  • Maintain healthy habits;
  • If necessary, wear protective masks to avoid contact with contaminated droplets in the air.

The H1N1 flu is a disease that can lead the patient to serious complications, which is why it is so necessary to emphasize how much vaccination and preventive measures are necessary. If you have any symptoms, see a doctor for diagnosis and seek immunization!

Share this information with your friends and family and thanks for reading!