The Role of Flu Shots in the Fight Against COVID-19

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Photo: Gracia Lam

While we anxiously await the development and approval of a safe and effective vaccine against COVID-19, there’s another health-sparing and lifesaving vaccine already available to nearly everyone over the age of 6 months.

Yes, that’s the flu vaccine, offered as an annual event that not nearly enough people partake in. The excuses are numerous, ranging from “I never get the flu” to “I had the vaccine once and still got the flu.”

The latter excuse is especially telling, reflecting a widespread misunderstanding of the nature and effectiveness of influenza vaccines that could carry over to any of the novel coronavirus vaccines that may ultimately reach the American market.

In general, flu vaccines are on average 50 percent effective in preventing infection by the main strains of influenza virus expected to be circulating in the country in the coming flu season, usually November or December to April or May. Flu vaccines are administered annually for two main reasons: 1) flu viruses mutate readily and the mix of viral strains varies from year to year, and 2) even if the viruses don’t change significantly, immunity against them gradually wanes and may be all but gone by the next flu season.

Be prepared, folks. A coronavirus vaccine may be no different. “If a vaccine was developed that is 50 percent effective in preventing COVID, it would still be licensed,” Michael T. Osterholm, infectious disease specialist at the University of Minnesota, told me. “Of course, we’d like a higher degree of effectiveness, but as with the flu vaccine, 50 percent protection is better than zero. A COVID vaccine probably won’t be nearly as effective as the childhood vaccines we’re familiar with,” Dr. Osterholm said.

Thus, even after being immunized against COVID-19, we may still have to practice social distancing, wear masks in public, wash our hands often and limit indoor gatherings until and unless this too-often lethal virus “disappears,” as President Trump once predicted it would. On the plus side, these protective measures against COVID-19 should also help to limit the spread of influenza. Indoors or out, masks can reduce the airborne transmission of both viral diseases, which spread when an infected person coughs, sneezes, talks, or sings.

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.

So who should be getting a flu shot? Not children younger than 6 months or people with certain medical conditions that may include those with a history of Guillain-Barrésyndrome or a prior severe allergic reaction to flu vaccine. However, according to the Centers for Disease Control and Prevention, most people with an egg allergy can safely get a flu shot. The vaccine contains inactivated virus so it is safe for those who should not be immunized with a live virus vaccine. But it’s best not to get a flu shot when you are not feeling well.

Some forms of flu vaccine are approved only for use in adults. For example, the recombinant influenza vaccine Flublok Quadrivalent, which does not use viruses grown in eggs, is suitable for those 18 years and older.

For people 65 and older, a three-component inactivated vaccine called Fluzone High-Dose is available and covered by Medicare. It is especially recommended for people living in nursing homes and other long-term care facilities. It contains four times the level of antigen needed to provoke an immune response than is found in standard-dose flu vaccines. According to a study published in The New England Journal of Medicine, the high-dose vaccine was 24.2 percent more effective in preventing flu in older adults than the standard-dose vaccine. Another study, published in The Lancet Respiratory Medicine, found that the use of the high-dose vaccine reduced the risk of respiratory-related hospitalization among nursing home residents.

In general, October is the ideal time to get a flu shot to help provide protection that lasts throughout the coming season, since the effects may wane with time. Given the pandemic, September might work better this year, but as my doctor told me, the best time to get it is when you can.

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