Dr. David States is the Chief Medical Officer of Angstrom Bio, which is located in Austin, TX. In the following Twitter thread, he explains the obstacles researchers face as they work to develop an effective vaccine for COVID-19.

Because this virus is so highly contagious, Dr. States writes, “a vaccine will need to induce durable high level immunity coronaviruses often don’t induce that kind of immunity.” He presents a study which shows that immunity starts to drops off after about two months.

COVID-19 has a high “R0.” (Some of you likely know what an R0 is, but since I did not, I’m including an explanation.) An R0 represents the disease reproduction number. How contagious is a disease? The higher the R0, the more contagious it is.

If each infected person spreads a disease to two people, it will have an R0 of 2.

Measles, for example, has an R0 of 12-18; Influenza, 1.4-1.7; Ebola, 1.5-2.5.

COVID-19 has an R0 between 3 and 5. Therefore, scientists will need to develop a strong vaccine to provide lasting immunity.

The best hope, is to produce a vaccine similar to the annual flu shot which is only about 50%. The flu shot, Dr. States says, even with a 50% rate of effectiveness, “still saves thousands of lives.” It also reduces the severity of the disease. The flu has a low R0, considerably lower than COVID-19.

The bottom line, he says, is, “yes, we all hope we’ll quickly develop a highly effective vaccine, but the biology of coronavirus and the history of veterinary vaccines suggests it may be a slog…A speculative hope is that a SARSCOV2 vaccine will reduce the severity of illness even if it doesn’t prevent infection altogether.”

The good news is that approximately 75 vaccine candidates are currently entering clinical trials. Dr. States writes that he would consider a vaccine a success if it merely reduced the severity of the disease even if it required an annual booster.

There’s a nice preprint just out on antibody responses to SARSCOV2. Lots of people don’t develop much of an IgM response and the IgG response fades noticeably after just two months 2/ https://t.co/5ayWt5rIND pic.twitter.com/nh6BtgGyvm

— David States (@statesdj) April 21, 2020

That means a vaccine will need to be quite effective if it’s going to stop the spread of SARSCOV2. The polio, measles and smallpox vaccines are really remarkable medicines inducing high level long lasting immunity, but not all vaccines work so well 6/

— David States (@statesdj) April 21, 2020

So even if only half the population takes the flu vaccine and it only works half the time, we are still knocking the effective infectivity down to 1 to 1.3 range which means the flu virus spreads a lot less quickly, far fewer people get infected and lives are saved 8/

— David States (@statesdj) April 21, 2020

Bottom line, yes, we all hope we'll quickly develop a highly effective vaccine, but the biology of coronavirus and the history of veterinary vaccines suggests it may be a slog. We need to keep working on antivirals, and we need to be prepared for extended social distancing 10/fin

— David States (@statesdj) April 21, 2020

12/addendum This Thread comes across as too pessimistic. There are ~75 vaccine candidates entering clinical trials. Hopefully some will be successful, and even if they “just” mitigate severe disease and require an annual booster that would still be a big a success

— David States (@statesdj) April 22, 2020

H/T: Greg P., Twitchy