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What are the downsides to vaccinating small children?

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.

1. Kids younger than five can finally get a vaccine. What downsides are there to vaccination?

The Pfizer and Moderna COVID-19 vaccines were approved by the CDC last Friday, and as of today there are 10 million doses distributed for free across the US for children 6 months of age and up who can start being vaccinated immediately. My two granddaughters will start their vaccinations this week. In testing of thousands of children, the vaccines have proven safe, with the side effects mostly irritability and crying, sleepiness, and loss of appetite on the day of vaccination. Infants and children vaccinated have not had the rare but self-limited side effect of inflammation of the heart called myocarditis. The vaccines are effective, generating higher anti-spike antibody levels than those seen in young adults. Finally, it is important to be vaccinated, as the omicron wave of the pandemic has been particularly hard on infants and children, with COVID-19 now the 5th leading cause of death in children.

2. My antigen test is still positive on day 11 of infection. Do I need to continue to isolate?

The official CDC recommendation is if you are continuing to improve and do not have a fever, you need isolate at home for only five days and can go out into the community wearing a tight-fitting mask to complete a total of 10 days of isolation. Exceptions to the 10-day rule have been immunocompromised people who might not clear the infection by day 10, and those who are staying ill, or who have the so-called Paxlovid rebound with a return in symptoms after completing the five-day course of this anti-viral. In all these exceptions, isolation should continue for another 5 days, or more. If you are still antigen positive on day 10, then you are likely still infectious and it makes sense to stay at home or to wear a tight-fitting mask until the test turns negative.

3. I hear that COVID-19 is going to be recirculating this summer because of two new omicron sub-variants, B4 and B5. These evade the vaccines and previous infections, from what I understand. With the number of these infections rising weekly, how do we stay safe?

The best way to stay safe is by getting the vaccine and its boosters even if you have had COVID-19 in the past. Wearing a mask in public indoor spaces as much as you can, and isolating yourself if sick until you know you do not have COVID-19 are also important. If you get COVID-19 despite these precautions, and there is no shame in that as I too have gotten omicron, then there are the anti-viral pills Paxlovid and Molnupiravir to take to help cure you.

And you are correct that the current BA2 variant of omicron is rapidly being outpaced by the BA4 and BA5 variants. BA4 and BA5 were first detected in South Africa in the New Year and likely arose from prolonged infection in individual immunocompromised persons, which allowed the omicron variant BA2 to mutate to BA4 and BA5. Today BA4 and BA5 are one third of all COVID-19 cases in the US and by the end of June will be the majority. So yes, one can expect that transmission will increase this summer from the already medium levels we are experiencing today in Charlottesville-Albemarle.

We talk about BA4 and BA5 together, as their Spike glycoprotein is the same, containing new mutations in the receptor binding domain that improve transmission and additional mutations that allow it to infect those who had immunity from the original omicron infection. The Pfizer and Moderna vaccines provide better immunity to BA4 and BA5 than does a prior omicron infection. The good news is that 83% of all Americans aged 5 and older have had at least one dose of a COVID vaccine. Also, good news is that the variants seem to have a harder time evading cell mediated immunity. That comes from being vaccinated or recovered from COVID-19), as it uses T cells and not antibodies to clear the infection. So, we should not see much of an increase in hospitalizations. Currently there are about 20 patients with COVID-19 at UVA Hospital, compared to over a hundred during the delta wave of the pandemic.

4. People with long COVID-19 face a range of symptoms; is reduced lung capacity one of them? Also, how long do these symptoms last?

Yes, reduced lung capacity can be part of the long COVID-19 syndrome, with shortness of breath upon exertion and diminished exercise capacity symptoms. This can occur anywhere from four weeks to a year from the initial COVID-19 infection and it is not known the extent to which these symptoms improve over time. The best explanation for long haul COVID-19 in my opinion is that the abnormal and damaging immune response seen with the initial infection persists in people with long haul. If this proves to be the case, it could usher in a new era of immunotherapy aimed at limiting inflammatory damage.

5. I know so many people who are getting COVID-19, but their symptoms are mild, much more so than the original cases in which thousands had to be intubated. Is COVID-19 still as serious an illness as it was when it first appeared?

COVID-19 infections are without a doubt less severe today than a year ago, and this is most likely not due to a less deadly virus variant, but because most of us are partially immune, either from being vaccinated or by having a prior COVID-19 infection. The cloud on the horizon is that immunity to coronaviruses tends not to be long-lived, for reasons we don’t understand. Maintaining our current high level of immunity through vaccination will go a long way towards limiting future deaths, which now number more than a million in the US. But until vaccines can be designed that last longer, this likely means all of us getting annual booster shots.

6. And are people who are not vaccinated getting more serious cases of COVID-19 than those who are?

Yes, the most recent data has shown that vaccination reduces the risk for hospitalization or death by at least 10-fold.


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