There are four types of Influenza Viruses – A,B,C, and D. While types A and B cause seasonal epidemics or “Flu Seasons”, C viruses are known to be more mild, and D viruses affect mainly cattle and are not known to affect humans.
Type A viruses are broken down into subtypes based on two proteins (HA and NA) on the surface of the virus, and then can be further broken down into genetic clades and subclades.
B viruses are broken down in a similar manner, but rather than subtypes based on surface proteins they are divided into two lineages before being further divided into clades and
sub-clades.Viruses are grouped into clades and sub-clades based on the similarities in their gene sequences. These different types of viruses are the result of a process called reassortment, which is the swapping of gene segments between viruses. This can take place when a host is simultaneously infected by two influenza viruses.
It is important to note that clades and sub-clades are genetically different from each other, but not necessarily antigenically different. Viruses have molecular structures on their surfaces that are known as antigens. When they are detected by the immune system they can trigger immune responses. Antibody production is an example of an immune response. The antibody or immune response triggered by the antigens on a virus are known as its antigenic properties. This means that when viruses are antigenically different from each other, immunity built up for one will not protect against the other. The reason for this is, when the antigens are different, the host’s immune system will not be able to detect the virus as easily. When the antigenic properties of viruses are similar, the immune system will be able to recognize them with more ease.
Seasonal flu viruses are detected throughout the entire year but are most common during the fall and winter months. The exact timing varies year by year, but activity of the viruses begin their incline around October, and generally peak sometime between December-February. High levels of activity have been known to last as late into the year as May.
Some of us are at greater risk for developing more serious complications from the flu.
Other risk factors include:
People that have the flu are the most contagious Within the first 3-4 days. They are also able to spread the virus as early as 1 day before the onset of symptoms, and as many as 5-7 days afterwards.
If you are sick with the Flu you should stay home and avoid contact with anyone else as much as possible unless you need to seek medical care. And it is recommended that you continue to stay home for at least 24 hours after your fever subsides.
If you are at high-risk, you should contact your doctor. They may prescribe antiviral medications to help combat serious complications. Antivirals are most effective if taken within 2 days of symptom onset.
There are some simple steps you can take to reduce your risk of not only getting the Flu, but spreading it too:
Getting your flu shot is the most effective way to protect yourself against the flu
Washing your hands often with soap and warm water or using hand sanitizer if you are in an environment where handwashing is not accessible
Cleaning/disinfecting frequently touched surfaces
Coughing/sneezing into your elbow rather than your hands
Not touching your mouth/nose/eyes with unwashed hands
Staying home if you are sick
Seasonal Influenza vaccines are designed to protect against the strains of Flu Viruses that are predicted to be the most common in the upcoming season as indicated by research. The antigenic properties of these strains indicate which strains will be included in the vaccine. The World Health Organization (WHO) will generally give their recommendations based on their findings around 6 months prior to the upcoming flu season to give vaccine manufacturers enough time to generate enough vaccines. Influenza vaccines are either Trivalent or Quadrivalent, meaning they either contain three strains or four strains, respectively. Trivalent vaccines contain two Influenza A strains, one strain from the A(H1N1) subtype and one strain from the A(H3N2) subtype. They also contain one Influenza B strain from one to the two lineages. Quadrivalent vaccines contain those same strains as well as one strain from the other B Virus lineage. Health Canada receives confirmation from manufacturers that their vaccines contain the antigenic strains recommended by the WHO for that upcoming Flu Season in the Northern Hemisphere. Health Canada has authorized all available vaccines in Canada. There are two categories of flu vaccine that are authorized for use here in Canada.
Within this category of vaccine there are two types, the first being Split Virus Vaccines in which the virus has been disrupted by a detergent. The second is Subunit Vaccines, in which HA and NA have had their viral components removed which purifies them further. IIVs are available in standard dose formulation, high dose formulation, and/or adjuvanted formulations (Adjuvants are substances added to increase potency and efficacy in vaccines). Standard formulations are unadjuvanted, quadrivalent vaccines with standard levels of the HA antigen, and are given as an intramuscular injection of a 0.5ml dose. Other authorized IIVs are trivalent and adjuvanted, referred to as IIV-adj. The high dose formulation authorized in Canada is an unadjuvanted quadrivalent vaccine with higher levels of the HA antigen administered as an intramuscular injection as a 0.7ml dose.
The influenza viruses that this type of vaccine contains are altered so that they do not cause influenza. This type of vaccine is administered as an intranasal spray as a 0.2ml dose (0.1ml in each nostril). The viruses are cold-adapted and temperature sensitive so that they replicate in the mucus membrane of the nasal cavity rather than the lower respiratory tract.
Once the vaccine is received, production of antibodies and therefore protection against influenza infection is achieved usually by two weeks, although some protection might be achieved before then. Vaccine effectiveness may vary from season to season as it depends on how well the strains contained in the vaccines match the strains in circulation during that particular season, as well as the health of the individual receiving it. Age, presence of immunocompromising conditions, as well as prior and subsequent exposure to antigens are also factors in the antibody response of an individual that has received the influenza vaccine.
Secondary, or booster, doses are not required within the same Flu Season. Children between the ages of 6 months and 9 years will require a second dose a minimum of 28 days after receiving their first dose only when it is their first dose ever received. Secondary doses in adults do not appear to have any effect on immune response in comparison to one dose.
When it comes to receiving vaccines cocominantly, there is a theoretical understanding that sequential administration of two live vaccines within 4 weeks of each other could reduce the efficacy of the second vaccine. But when it comes to unadjuvanted Inactive Influenza Vaccines, studies have shown that receiving the Flu Shot simultaneously with recombinant zoster vaccines ,such as Shingrix , and pneumococcal polysaccharide vaccines such as Pneumovax23, is safe. The Flu Shot may also be administered simultaneously with the Covid19 vaccines. If multiple vaccines are given in one clinical visit, it is ideal that they are administered in different limbs, although if that is not possible then they may be spaced out a minimum of 2.5cm (1 inch) apart.
Common adverse events following influenza vaccination are mild reactions at the site of injection that tend to resolve themselves within a couple of days. High dose (IIV-HD) tends to induce higher rates of systemic reactions than standard dose (IIV-SD), but again these reactions are mainly mild and tend to resolve themselves quickly. Runny nose and nasal congestion are common adverse events for those who receive the Live Attenuated Influenza Vaccines administered as an intranasal spray. Again, these tend to be mild and short lived.
Optimum Pharmacy
615 Davis Dr. Unit#101, Newmarket,
ON L3Y 2R2
