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Dr. Petri talks about the polio vaccine and COVID-19 vaccines & boosters

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.

I am going to New York City in October. Do I need to have my polio booster vaccine before going?

If you have not been vaccinated against polio, then you should get vaccinated, even if you are not traveling to New York City! Note that it would be unusual not to have received the polio vaccine, as it is part of the childhood vaccines that we all receive. However, if you missed it, or don’t know if you received it as a child, it is a simple process to “catch-up” with two doses, one now and one in four weeks’ time. The vaccine that you would receive is the Salk vaccine (named after Jonas Salk who invented it in 1954) which contains the inactive virus. It is highly effective at preventing paralysis from polio and does not carry the tiny (one in a million) risk in the Sabin polio vaccine of the vaccine virus mutating to cause paralysis.

By the way of background: Poliovirus transmission in New York City was identified when an unvaccinated man became paralyzed from polio in June of this year. This was the first case of polio in the U.S. in nearly a decade. The man had not traveled internationally in the preceding three weeks (the incubation period of polio), so he was infected in the City. The poliovirus that caused his paralysis was sequenced and shown to be derived from the Sabin live virus polio vaccine. This Sabin vaccine is used overseas in the Global Polio Eradication Initiative as it prevents both infection and paralysis.

While no one else has been paralyzed, this mutant virus has been detected in wastewater from four different counties surrounding New York City, and in London and Israel. Since there are hundreds of asymptomatic polio infections for every case of paralytic polio, this suggests that thousands of people are unknowingly infected with poliovirus in New York City, London and Israel. There is the potential for additional cases of paralytic polio in the New York City area, as rates of polio immunization of children under five there are as low as 70%. With the current state of emergency declaration in New York state, the recommendation is for all unvaccinated New York residents aged two months and older, including pregnant women, to be immunized immediately. Boosters are also recommended for previously immunized healthcare workers who treat patients who might have polio.

Is the new bivalent booster going to provide lasting protection, or is this more like the “whack-a-mole” game where new variants keep coming up?

Good question! This is going to be a good booster, despite the mutations we continue to see in the SARS-CoV-2 virus. To back up for a second, this new bivalent vaccine contains mRNA for both the ancestral strain from Wuhan, China as well as the currently circulating BA.4 and BA.5 strains. The BA.4 and BA.5 strains have identical spike glycoproteins. They are currently 90% of all COVID infections as of Sept. 10, so the good news is that the bivalent booster will provide much better protection against the viruses currently causing COVID-19. There is a newer omicron subvariant that is derived from BA.4, called BA.4.6, and so far this seems to be replacing BA.4 but not BA.5. So, I expect that I personally, and most all of us who are boosted, will see extended protection through the worrisome winter period.

When should I get the new bivalent booster? I had COVID-19 in August is why I ask.

It’s so exciting that the bivalent booster is actually already available here in Charlottesville!

Everyone age 12 years and older is eligible for a booster. Since you just had COVID, you should wait for 3 months (November) to receive the bivalent booster. This recommendation is based in part on the fact that the immunity that you received from the infection will start to decline.

While I am thinking of it, the only other reason for a wait to be boosted is a two-month period after you received the original booster. I got mine on Saturday at local drugstore, and it was a very easy in-and-out!

Just so you know, the goal with the bivalent booster is to have high levels of immunity in the U.S. population this fall and winter against the new omicron subvariants BA.4 and BA.5, so that we do not have another December-to-January peak in COVID-19. This was a huge problem when the original omicron variant arrived from Africa in 2022 with up to a million cases per day, and in 2021 when the alpha variant from the United Kingdom caused several hundred thousand infections per day.

At the UVa Hospital as of Sept. 9, we have 33 patients with COVID-19, four of whom are in the ICU. This number is fortunately not the 100+ cases we had at the height of omicron. This is because there are currently high levels of immunity in the U.S., as most everyone has been vaccinated, infected or both. The concern is that with the decline in protection that happens in the months after infection or vaccination, without this bivalent booster we will again this winter have many people hospitalized with severe COVID-19. And sadly, not only at UVa, but across the U.S., one in every eight patients admitted with COVID pneumonia dies. Our extended family lost a young father who had not been vaccinated, so this risk is very real to me.

For those people 50 and older and/or immunocompromised who received their second booster in the last few months, is it recommended that they also receive this booster which is geared toward the omicron subvariant?

Yes! The new bivalent booster is recommended for everyone ages 12 years and older. One should wait for two months after receiving the old booster, and three months after having had a COVID infection, but the rest of us should get it ASAP. It is going to do a much better job of protecting us from the BA 5 variant that is currently causing most infections.

I tested positive for COVID eight days ago. I have no symptoms now, but I just tested positive today. I am supposed to go on a business trip Thursday. Is it safe for me to travel if I mask?

I would postpone the trip so as not to run any risk of exposing others. But this is not the CDC guidance for someone like you who has no symptoms: CDC would have you isolate at home for the first five days of infection with COVID-19 and then be out and about but wearing a mask for an additional five days. I am more cautious, as the at-home tests for COVID-19 are a fairly reliable way to determine if you are still infectious. So my advice would be to stay home until negative.


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