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Dr. Petri answers your COVID-19 questions, explaining how viruses evolve and when it's safe to visit friends and grandkids

University of Virginia immunologist and COVID-19 researcher Dr. William Petri continues to answer reader questions about COVID-19, vaccines and, now, the omicron variant.

Omicron causes less severe symptoms in most cases. Does that possibly mean SARS-CoV-2 is also weakening? Could this bring us closer to the end of the pandemic?

I agree with you that infection with the omicron variant of SARS-CoV-2 is less severe than the earlier delta variant of SARS-CoV-2 (the virus that causes COVID-19). We saw this in South Africa, where the peak of omicron infections was thankfully not followed by a peak of deaths due to COVID-19, and in the United Kingdom, where the rate of hospitalization appears to be as much as 50% lower. There are several explanations for this, including, importantly, that many of the infections are happening in people who are protected from more severe disease by having received the boosted vaccine.

But you are right that the virus itself seems to be less deadly. The best evidence comes from animal model studies of COVID-19, where infection with omicron causes a less severe pneumonia than infection with delta. Respiratory failure being the most common reason for evidence that omicron causes less severe infection, hospitalization and death due to COVID-19, this is good news. However, I would not let down your guard, as a COVID-19 infection that is half as severe as delta is still nothing to sneeze at (pun intended). With the incredible rise in omicron infections this week, the University of Virginia Hospital has a record number of COVID-19 admissions.

We are all hoping that the SARS-CoV-2 virus will continue to become less deadly, if more transmissible. Mutations in the virus that make it spread faster between people are being selected by evolution because a virus such as delta that does not spread as fast gets out-competed. Viral mutations that make the infection less severe might also be selected for through evolution, as someone who is sick at home in bed with a bad infection will be less likely to spread infection.

Does having omicron give me natural immunity? In other words, if I made it through omicron, am I safe?

There is natural immunity that comes with recovering from COVID-19. I recommend that you still get vaccinated, if you have not already, as we know that vaccination after recovery from a delta infection gives added protection. The vaccines are also a much safer way to gain immunity than is suffering through a COVID-19 infection! We know that vaccination provides substantial, about 10-fold, protection from being hospitalized or dying from COVID-19.

Several friends and I – all in our 70s – are planning a day trip for shopping and to have lunch to fight the January blues. We are all vaxxed and boostered. We would all be in the same car, to and fro, for about an hour each way. Is it safe for us to continue with our plans? This sounds delightful by the way; what a great way to enjoy one another’s company! You and your friends are all doing exactly the right thing by being vaccinated and boosted, and as a result are much less likely to have a serious omicron infection. Omicron, however, has mutated in a way that makes vaccines less effective at preventing infection. Protection after boosting is 90% at keeping you out of the hospital but closer to 70% in preventing infection. Add to this omicron being more transmissible, we are experiencing ten times the number of reported infections right now, 700,000 today compared to 70,000 during the delta wave at the beginning of November. Thus the chances of catching COVID-19 unfortunately have never been higher; I am seeing this in my family, with three of my children infected in the last week! I don’t want to put a damper on what sounds like an important social event though, and there are additional safeguards you could put in place to make the shopping trip safer. These include everyone doing a rapid at home test for COVID-19 the day prior (with a little persistence these are available at pharmacies in town), and not including anyone on the trip with cold or flu symptoms or who has been exposed in the last 5 days to someone with COVID-19. Wearing masks in indoor public spaces also can help reduce exposure. And do make sure everyone has received the annual flu shot. If not, it is not too late, as we are just getting into the annual winter flu epidemic.

I had the booster relatively early. Last week, you suggested that we may need to get a second booster. But I’m also hearing that with so much omicron circulating, that we are building up natural immunity. Is that true? Also, if we gain natural immunity from the omicron variant, does it also mean we would gain immunity from all other variants?

About 200 million people in the U.S. have been vaccinated, so there may be as many as 100 million without any immunity. If we get up to a million or more cases of omicron a day, which seems likely, then the gap between immune and non-immune will close rapidly. So I think you are right that due to omicron the U.S. population will have a greater degree of immunity, but at a cost of suffering that could have been avoided by vaccination and boosting.

Just to add a bit, we have all heard that there are two arms of the immune system, antibodies made by B cells that prevent us from getting infected, and cell mediated immunity done by T cells that cure an infection after it has started. T and B cells are activated by both natural infection and vaccination, so as the pandemic wears on, one can expect to see less severe illness due to the B and T cells of the immune systems protecting us, as well as the virus evolving to be less virulent – so good news!

Is the original coronavirus even circulating any more?

Just a tiny bit. The latest data from the CDC on January 1 shows that omicron is 95% and delta 5% of COVID-19. This is true for most of the country with the possible exception of part of the Midwest, where there may be up to a quarter of infections still being due to delta. Here at UVa, Dr. Amy Mathers is sequencing every SARS-CoV-2, with her most recent data showing 66% omicron right before Christmas. Amy mentioned to me that while the sequencing is still ongoing, she expects we are like the rest of the country with nearly all omicron today.

Because I was traveling abroad I got a full dose booster of Moderna on August 20. Am I still protected?

Likely you are. I mentioned last week that data from the United Kingdom is indicating that the protection from the Pfizer booster may be waning at 4 months; so far, this does not seem to be the case with the Moderna booster.

If an adult has not received their booster because it has not been six months since their second dose of the vaccine, are they considered a ‘safe’ contact until they reach the six-month mark? For example, if a family wants to meet indoors and some family members are boosted, but some are not because they are not yet due for their booster, do any extra precautions need to be taken?

Yes, they are “fully vaccinated” even if not boosted if they are within 5 months of completing the initial vaccination. There is, however, a gradual decline in the effectiveness of the vaccine over the five-month period after vaccination. For example, one is less protected at four months than two months after vaccination. I think with family gatherings in this month of omicron spread, one should be extra cautious, but not to the extent of canceling activities that involve vaccinated people. Rapid antigen tests prior to a family reunion and attention to adhering to isolation and quarantine guidelines will help. But of course almost half of my immediate family has been infected (none seriously) in the last week despite these precautions, so I am perhaps not one to talk!

If children are to be included in a family gathering where the adults are fully vaccinated, but the children are not vaccinated or only partially vaccinated, should masks be worn? If so, by whom—adults, children, or both?

Well, as with a lot of things, it depends. Children who are under five (and therefore not able yet to be vaccinated) can be a source of infection. This is much less likely if they are not yet in day care or school, where they are exposed to non-family members. If children are exposed, the CDC recommendation is for children older than two to wear masks indoors at the family gathering, whereas the adults would not need to. I am sure you share with me the hope that soon we will be able to protect our youngest with the COVID-19 vaccine.

Is it safe for fully vaccinated and boosted adults (grandparents) to visit with grandchildren who are too young to receive the vaccine?

Mary Ann’s and my favorite activity is visiting our granddaughters in Tampa! Aren’t they the greatest! Like you, we are vaccinated and boosted. As added safeguards we get tested for COVID-19 the day prior to our visit, and we would delay a visit if exposed to someone with COVID-19 (until completing a five day quarantine).


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