BLOOMINGTON – Recently approved COVID-19 vaccines have been shown to be more than 90% effective, and those who have been infected and recovered can expect to have some immunity from the disease, at least for a few months.
But can someone with immunity, from infection or vaccination, still spread COVID-19 to others?
“At this time, we still do not know that,” said Graham McKeen, assistant university director of public and environmental health at Indiana University.
Despite an international effort to quickly learn as much as possible about SARS-CoV-2 — the virus that causes COVID-19 — much is still unknown because it has only been around for about a year. That’s why public health experts are still encouraging everyone to practice COVID-19 prevention behaviors, even as vaccines become available.
McKeen acknowledged most experts believe COVID-19 vaccines prevent transmission as well as the disease, but they don’t know for sure. And even it is eventually proven the vaccines can prevent transmission, it’s also important to remember that no vaccine is 100% effective in 100% of people 100% of the time, he said.
COVID-19 has already proven to be a disease of exceptions. While the vast majority of people who are infected survive, that’s not true for everyone. Symptoms can vary widely and while reinfection seems rare so far, it’s still possible. The Regenstrief Institute estimated the likelihood of reinfection at about one in 1,000, McKeen said. The duration of immunity after inoculation or infection is still not known.
Mutations in the SARS-CoV-2 virus are adding an additional layer of uncertainty to the situation. Experts have previously pointed to 70% as the minimum inoculation rate needed to achieve herd immunity. But new, more contagious variants, such as one that has emerged in the United Kingdom and spread to the United States, could push that threshold higher.
For instance, measles is one of the most contagious viruses in the world. One case in an unvaccinated population typically generates 12 to 18 more cases. By comparison, one case of COVID-19 is thought to typically generate 2.5 new cases. This greater rate of infection for measles is why public health experts say 95% of a population needs to be vaccinated to prevent an outbreak.
Exceeding 70% vaccination for COVID-19 in the U.S. has already proven more challenging than expected. Federal officials said in early December 2020 their goal was for 20 million people to receive their first shots of COVID-19 vaccine by the end of the year. So far, only about 12 million doses have been given. President-elect Joe Biden has said that he hopes to have 100 million vaccinated in his first 100 days in office, but that end date is still more than three months away.
That leads McKeen to suspect mask-wearing, physical distancing and other preventive measures will still be advised throughout 2021 and maybe longer.
That kind of estimate can be discouraging, especially for people who saw their own vaccine or recovery from infection as a ticket back to pre-pandemic life. But McKeen suggested looking at it from a different perspective.
“How terrible would someone who has natural immunity or from a vaccine feel if they passed (COVID-19) on to someone else?” he said.