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Dr. Petri answers your COVID-19 booster questions (and yes, it's OK to get flu shot at same time)

University of Virginia immunologist and COVID-19 researcher Dr. William Petri continues to answer reader questions about COVID-19. Send your questions to Lynne Anderson at, and she will forward them to Dr. Petri.

With mask wearing, social distancing, antibacterial lotion on our hands after every visit to a store, doctor, etc., and then washing our hands when we get home, we haven’t had any colds since the start of the pandemic. But, are these practices weakening our immune systems since there are so few germs to combat? And, if so, is that dangerous?

Being safe by wearing a mask and washing hands is not weakening your immune system. Our exposure to microbes (viruses, bacteria, fungi, and parasites) shapes and develops the immune system. But the microbes that cause us to become ill are less important for a healthy immune system than the beneficial microbes that inhabit our bodies. The “microbiome” is the scientific term for the multitude of beneficial microbes that inhabit our gut, skin, sinuses, lungs, and reproductive tract.

Exposure to the microbiome is extraordinarily beneficial to human health. This is because during the last 2 billion years of evolution, the microbiome has co-evolved with us in a mutually beneficial way. The microbiome teaches our immune system during childhood to protect us from not only germs but cancer, and to maintain balance between protection and harmful inflammation. Here at UVa, we have the Trans-University Microbiome Initiative that Dr. Sean Moore and I co-direct, and that is actively investigating how to harness the microbiome for health.

And by the way, congratulations on your good health! I am sure you have also received the bivalent COVID-19 booster and the flu vaccine and are role models for all of us!

I am trying to decide optimal timing for updates of the COVID-19 booster. I’m currently four months out from infection with B.2.12.1. The CDC is recommending waiting three to six months from natural infection if you were sick with an omicron variant. I was hoping to stretch out to five months (mid November) to maximize time of protection, but with the NYC marathon coming up, wondering if I should just get it now? Somewhat concerned about running with 40,000 people!

You could stretch things out to five months, which likely would give you higher levels of protection in the winter. But with the NYC marathon coming up next month I personally would get the booster. I just ran the Chicago marathon with 50,000 other runners and over a million spectators and was glad to have received the bivalent booster in advance! Have a great race – what a wonderful experience awaits you!

I am 71 years old and have chronic lymphocytic leukemia. I had no antibody response to any of the three Moderna vaccinations I received. For CLL patients and other immunocompromised people who do not have a vaccine response as measured by detectable antibodies, is there hope of other treatments that might provide some level of protection for us now or in the future? In one article I read, someone said, “It is NOW time to give monoclonal antibodies to ALL blood cancer patients who don’t respond to vaccines. . . especially if the long-acting forms are used.” What do you think?

I am so sorry that you have CLL and that it has prevented you from having a protective antibody response to the Moderna vaccine. You can be protected from COVID-19 by receiving a shot of the anti-SARS-CoV-2 monoclonal antibodies tixagevimab plus cilgavimab (Evusheld). This cocktail of monoclonal antibodies is administered as two shots intramuscularly and needs to be repeated every six months. What Evusheld does is to give you the anti-spike antibodies that your immune system was not able to make normally to the vaccine. The community of Charlottesville participated in the early multi-site clinical trials that I led locally that showed the benefit of anti-spike monoclonal antibodies in prevention, so you can thank your neighbors for this advance!

If having a case of COVID gives us antibodies and if immunity due to the presence of antibodies protects us from COVID-19; why don’t we offer antibody testing to those who don’t want the vaccine?

You can get tested for antibodies against the spike glycoprotein of the COVID-19 virus to see if your body has mounted a protective immune response from either infection or vaccination. The reason that this is not done routinely is that vaccination improves upon the immunity that one receives from natural infection. So, we would not want to keep someone from being vaccinated just because they had antibodies from a prior infection, as they would still have better protection from also getting the vaccine.

It is amazing to me that over 900 million doses of the mRNA vaccines have been given in the U.S., with a proven track record of safety and efficacy. Everyone ages six months and older should get a COVID-19 vaccine as soon as they can. And most of us also need the new bivalent boosters, as protection against mild and moderate COVID-19 wanes over several months’ time. Only 68% of the US population is fully vaccinated, and most have not received the bivalent booster. Vaccination reduces the chances of being infected 3-fold and of dying 6-fold. With 400 people dying each day in the U.S. of COVID, vaccination is a tragically missed opportunity for many of us.

On Oct. 12, the CDC came up with new guidelines for masking, suggesting, if I am correct, that people need to mask only if case levels in their areas are high. Is this correct, and does this allow adequately for the weekly variation in case rates? Bottom line: should I still wear a mask when I am in public?

Fortunately, right now we have low levels of transmission in Charlottesville and Albemarle County. The CDC recommends that during low transmission that we continue to wear masks on public transportation, as well as in any indoor public space if at greater risk for severe COVID-19 (age greater than 65 years, heart, or lung disease or immunocompromise). I agree with you that it make sense to keep track of the levels of community transmission so that you can increase preventive measures such as masks and social distancing at higher transmission levels.

In that same update, the CDC changed its guidance on quarantining and isolation. I am confused. Does the same guidance apply to those who had a “weak,” or light, case as to those who might have been sick for weeks?

Yes, the same guidelines apply to all: Isolate yourself for at least five days if you have COVID-19; if you are better then, you can end isolation but continue to wear a mask in public for an additional five days. For those of us who are fully vaccinated, quarantine is not required after exposure to someone with COVID-19, although it makes good sense to wear a mask in public for 10 days. By the way, it is important to test yourself or family members for COVID-19 when cold and flu symptoms occur for two reasons: to prevent exposing others and to receive anti-viral treatment.

In recent weeks, I’ve had two friends get very, very sick with COVID, though neither case required hospitalization. Both were vaccinated; one was in her 30s, which somewhat goes against the conventional wisdom that only older people are getting very sick with COVID. My question is: Are we now being too lax in observing COVID safety precautions? How big a threat is COVID now that winter is approaching and, with it, flu season?

How fortunate that both your friends had been vaccinated, as we know that the vaccine reduces death by 6-fold. Young age is not totally protective, as approximately 70,000 Americans under the age of 50 years have died so far from COVID-19. We are protected from the worst of COVID-19 through immunity provided by vaccination and prior infection, and from the new antiviral medicines Paxlovid and Molupiravir.

However, we should keep our guard up for two reasons: First the SARS-CoV-2 virus continues to evolve (currently only 70% of COVID-19 is due to the BA4/5 variants that are in the bivalent booster, compared to 98% at the end of August), and immunity from the vaccine or natural infection wanes over several months to be less protective. Fortunately, we are in a much better position to respond to the next wave of the pandemic through vaccination, anti-viral pills, and returning to masks and social distancing when transmission levels go back up.

I’ve read that Florida’s surgeon general is advising young men to not get vaccinated, based on what some consider a rather flimsy study that suggests they are at much higher risk of a heart problem called myocarditis. What do you think young men should do, as in Charlottesville, we are surrounded by students who fall into this category?

As with a lot of falsehoods, there is a tiny bit of truth mixed in. The mRNA vaccines cause, in 1 in 100,000 young men, a self-limited inflammation of the heart called myocarditis or pericarditis. Both the CDC and the independent Advisory Committee on Immunization Practices recommend that young men receive the mRNA vaccines, as the risk of COVID-19 far outweighs the rare problem with heart inflammation, especially since the myocarditis heals on its own in almost all. Thanks for asking this – it is an important point.

Uptake of the latest booster seems to be low. Do you any numbers available on how many have received this booster compared to the previous ones at the same point of their rollout? And should we all get boosters – is there any case in which they are not warranted?

About 43 million people have received the new bivalent boosters as of last week, so most Americans are not optimally protected from the next wave of the COVID-19 pandemic that we expect this winter. Everyone six years of age and older is eligible to receive the new booster shot. You should get the booster at least two months from your last shot of the old vaccine or booster, or three months from having a COVID-19 infection.

Is it OK to get the booster and flu vaccine at the same time?

Absolutely, and how convenient!


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