Since we already know that the antibodies people develop following a coronavirus infection seem to wane with time, there’s a good chance that any coronavirus vaccine would need to be administered repeatedly, perhaps annually, to provide adequate protection. Unlike the flu, Covid-19 has shown no evidence of having a season. Whether the weather is hot, cold, dry or wet, this coronavirus is highly infectious. But like the flu, it spreads readily from person to person, and can be transmitted even before those infected know they are contagious as well as by those who are infected and don’t become noticeably ill.
Another fact worth noting: the flu vaccine does not and cannot cause the flu. Some people may get a feverish reaction to a flu shot, but that may represent in part the body’s effort to muster an immune response. Or, as Dr. Osterholm pointed out, those who get the flu within a few days of being immunized may actually have another respiratory bug or may have already been infected with the flu virus when they got the shot. Flu viruses typically have an incubation period of one to four days before symptoms develop, and it takes about two weeks for the vaccine to become fully protective.
However, even if people do get the flu after being properly immunized, the illness is likely to be significantly less severe. This may also be the case with a coronavirus vaccine.
Experts are currently most worried about a likely confluence this winter of a flu epidemic and a still-raging Covid-19 pandemic, which could easily overwhelm the medical care system and create anew a shortage of hospital beds and personal protective equipment. Pneumonia is a not-uncommon complication of the flu that could add to the burden of hospitalizations needed for people with a life-threatening coronavirus infection.
The experts are also concerned about people who develop the flu and, thinking it could be Covid-19, seek medical care and a test that could inadvertently expose them to this dreaded virus as well as cause a shortage of tests. Both ailments can produce similar symptoms: fever, cough, shortness of breath and fatigue that can be extreme.
Another worrisome possibility is that people who get the flu might be even more susceptible to contracting the coronavirus and to developing severe disease.
Even discounting an increased risk of Covid-19, the complications of flu can be serious. They include bacterial pneumonia, ear infections, sinus infections, and a worsening of chronic medical conditions like asthma, diabetes and congestive heart failure. Others at increased risk of serious flu-related complications include people 65 and older, pregnant women and children younger than 5.