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Epidemiology assistant professor Michael Mina discussed the threats that some variants of the coronavirus may pose — despite the fact that tens of millions of people in the U.S. are now fully-vaccinated — during a Harvard School of Public Health Event on Tuesday.

In the forum jointly held by the School of Public Health and The World, a media organization, Mina said that though “not all variants are worrying” — and many are a “normal part of virus biology” — variants that cause the virus to transmit more, cause worse symptoms, and evade the immune system may be concerning.

The issue of invariant transmissibility has more to do with the fact that the virus stays at its peak for longer, rather than the way the virus transmits, according to Mina.

“We believe that the increased transmissibility is generally that the virus has a greater fitness inside the body, meaning it can stay at high amounts of virus for longer and therefore increase its potential to spread to another human,” Mina said.

Mina said the invariants do not currently appear to cause different symptoms than the original coronavirus strain.

When a large proportion of the population is vaccinated, Mina said it is crucial to focus on whether an invariant can escape immunity induced by the current vaccine.

“If we start to see variants escape immunity, then that might mean that we have to go back and boost people with a new vaccine that covers that particular variant,” Mina said.

This may result in an undesirable game of “catch-up” from constantly needing to boost the vaccine for a new invariant, he added.

Mina said there could be a possibility of a universal vaccine, one that “can attack multiple or could protect against multiple different lineages of this virus at once.”

For now, since immunity may wane most quickly in the elderly, they are the ones of utmost concern, Mina said.

“My personal concern is, as the elderly people are the very people we’ve been trying to protect during this virus pandemic, and because they’re the most susceptible, unfortunately, the oldest age classes are also the least equipped to get a new vaccine and really retain immunological memory,” Mina said.

For the vaccinated and unvaccinated alike, exposure to Covid-19 depends on behavior, like wearing masks, and also whether the virus can grow in one’s body, which could happen even in those who are vaccinated, Mina said.

However, viruses growing in a host that is already immune potentially "boosts our immune system" because "it gives us a reminder of the virus that we’re trying to protect ourselves against.”

Mina acknowledged that the vaccines has proven very effective against preventing the most severe symptoms of Covid-19.

“If you’re fully vaccinated, it’s very, very, very unlikely that you will get a severe disease, even if you get exposed and infected with this virus,” Mina said.

Even with widespread vaccinations, Mina sees easily accessible and cheap rapid tests as one of the most important measures that should also continue to be developed to prevent community spread.

“We have still not gotten around to realizing that testing in a pandemic is for public health, not medicine, and we should not be charging anyone, frankly, for using a PCR test,” Mina said.

—Staff writer Alexandra Topic can be reached at alexandra.topic@thecrimson.com.