The typical annual flu season lasts from late fall to mid-spring. The two strains (A and B) peak at different times, with A strains peaking earlier (January-February) and B strains peaking in the Spring. The vaccines are usually released in early Fall, though some chain stores have already received them early August this year.
Following vaccine administration, the immune system takes 2 weeks to produce antibodies that are responsible for the protective r
esponse against the flu. Unfortunately, these antibodies begin to decline 40 days after the vaccine. A 2018 study published in Clinical Infectious Diseases indicated that risk of influenza infection starts to increase 40 days post-vaccination. Compared to "controls" (defined as 14-41 days post vaccine), the risk of a positive influenza PCR (collected via nasal swab) increased by 32% at days 42-69, and continued to increase by 16% for each additional 28 day period, peaking at around 206% at 155+ days.
Hence, CDC is currently recommending that people receive their annual flu shot starting in OCTOBER to ensure that antibody titers are high during the anticipated season peak and persist through the end of the possible risk period. I usually recommend people get their flu shots between mid-October and mid-November unless extenuating circumstances exist and then they should continue to receive immunizations until end of May. Flu vaccine is recommended even if someone thinks they may have already gotten the flu that season since the vaccine protects against multiple strains. Individuals over the age of 65 should receive one of the high-potency vaccine formulations (if not available, receiving regular potency vaccines is preferred over waiting).
We are anticipating high demand for flu vaccines this season to decrease respiratory disease burden, visits to doctors, and hospitalizations among at-risk individual since it is highly likely that we will be experiencing surging COVID-19 cases at the same time and co-infections with the two may possibly occur. The people at greatest risk of influenza and its complications are young children, the elderly, and those with metabolic, respiratory, immune, and cardiovascular disorders. While the CDC recommends that everyone receive the vaccine (unless contraindicated), it is very particularly important for those that come into contact with at-risk individuals to be vaccinated to decrease risk of transmitting the flu to the vulnerable.
Please call your vaccine provider of choice to make an appointment for OCTOBER now to reserve your vaccine dose in case there are shortages later this year (which is not uncommon).